the application of internal grading system technologies for agricultural products â€“ review

Journal of Food Engineering 116 (2013) 703–725

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Journal of Food Engineering

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Review

The application of internal grading system technologies for agricultural products– Review

Meftah Salem M. Alfatni a,⇑, Abdul Rashid Mohamed Shariff a, Mohd Zaid Abdullah b,Mohammad Hamiruce B. Marhaban a, Osama M. Ben Saaed a

a Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysiab School of Electrical and Electronic of Engineering, Universiti Sains Malaysia Engineering Campus, 14300 Seri Ampangan, Penang, Malaysia

a r t i c l e i n f o a b s t r a c t

Article history:Received 4 April 2012Received in revised form 21 December 2012Accepted 2 January 2013Available online 16 January 2013

Keywords:Internal grading systemAgriculture cropQuality inspectionSignal processing

0260-8774/$ - see front matter � 2013 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.jfoodeng.2013.01.001

⇑ Corresponding author. Tel.: +60 389467543 (O), m+60 389466425.

E-mail addresses: [email protected], MefAlfatni).

Quality assessment of agricultural products has been the subject of numerous reviews; however, notmany papers address internal visualization as a means of quality grading. This paper reviews establishedas well as emerging visualization techniques utilized in the quality assessment of food products. In thisdiscourse, the authors set out to underscore some of the most novel signal processing techniquesemployed in the non-destructive grading of agricultural products by way of an automated quality veri-fication system. Such systems utilize advanced engineering principles with imaging, signal processingas well as color differentiation to accomplish the grading task. The materials presented will be usefulto agricultural engineers, manufacturing engineers, food engineers and any other researchers in the foodand agriculture industries.

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Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7032. Internal grading system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 704

2.1. System design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7052.2. Signal processing steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 705

3. Methods and techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 705
3.1. Fruit moisture measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7063.2. Fruit sugar measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7083.3. Fruit acid measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7103.4. Fruit ripeness measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7123.5. Fruit damage measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 714
4. Discussion and conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 718Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 721References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 721

1. Introduction

Agricultural product quality grading is based on two inspectiontypes namely; agricultural external grading systems which havebeen reviewed previously by Alfatni et al. (2011) and agricultural

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product grading based on internal quality assessment which hasgained untold prominence in the recent past. Although traditionaltechniques have been employed since long before, they are greatlytedious, costly and time consuming. The previously used systemsare also thought to suffer severely from subjective inferences lead-ing to inconsistencies (García-Ramos et al., 2005). Even where thissystem is regarded as unbiased, the system fails to support thelarge-scale production requirements of our current time. It isagainst this background that high-technology solutions are beingsought to make use of machine vision for quality, timely assess-

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Fig. 1. Internal and external of tomato fruit samples at different ripeness stages (Qin et al., 2012).

Fig. 2. Diagram of the experimental set-ups for the measurement of the impedance spectra of willows. (A) The stem with the whole root system in the solution (‘Stem androot’). (B) A single root in the solution (‘Root’). (C) The stem only in the solution (‘Stem’). E1 and E2 refer to the Ag electrodes (Cao et al., 2010).

704 Meftah Salem M. Alfatni et al. / Journal of Food Engineering 116 (2013) 703–725

ment and accurate grading of agro-based products (Malamasaet al., 2003). This technology is suitable to perform surface orsub-surface imaging due to the limited penetration depth of theinterrogating source. The recent past witnessed a mass innovationof newly developed automated internal grading solutions byresearchers around the world (Alfatni et al., 2008; Leemans andDestain, 2004; Njoroge et al., 2002).

Such a system is composed of a PC with the required operatingsystem (OS) and programming language (PL) installed and fitted tospecial sensors to read such internal characteristics as moisturecontent, sugar level etc. (Abdullah et al., 2004; Brezmes et al.,2000; Jaren and Garcia-Pardo, 2002; Kwak et al., 2007). Based onthese metrics, the system sorts the products into different gradesbased on all other factors involved, some of which we shall relate.

2. Internal grading system

Fruit quality is related to both internal (firmness, sugar content,acid content and internal defects) and external (shape, size, exter-

nal defects and damage) variables (García-Ramos et al., 2005). Fruitinternal grading is one of the quality grading systems used in agri-cultural research as illustrated in Fig. 1 (Qin et al., 2012). Internalcharacteristics such as moisture, sugar, acidity and the like offervaluable information about fruit ripeness, which may not be easilydetected by merely examining the fruit’s external characteristics.Njoroge et al. (2002) devised an automated quality verificationtechnique via the internal inspection of agricultural products usingspecial sensors for sugar and acid content estimations. They incor-porated an X-ray sensor to detect possible biological defects. Ananalysis of the willow root system by electrical impedance (EI)spectroscopy (EIS), as shown in Fig. 2, was conducted by Caoet al. (2010). EIS was proven to be a valuable, nondestructive meth-od for root surface area assessment. This technique could be con-sidered a novel methodological contribution to facilitate furtherunderstanding of root systems and their functions in a nondestruc-tive manner. The sensor plays an integral role in the algorithm (Duand Sun, 2004). Internal constructions are not easy to detectthrough comparatively simple and traditional imaging means,

Fig. 3. (a) Hyperspectral imaging system developed at the Agricultural Product Processing and Storage Laboratory, Jiangsu University, in Zhenjiang, P.R. China and (b) sketchof the system (Zhao et al., 2009).

Meftah Salem M. Alfatni et al. / Journal of Food Engineering 116 (2013) 703–725 705

which cannot offer sufficient information concerning internalfaults such as water-core, internal breakdown and hollow heart.In addition to the aforementioned techniques, Ultrasound, MRI,CT, and ET technologies are some of the probable solutions to thechallenges of inspecting interior attributes.

2.1. System design

It could be recalled that the application of grading systems inagricultural product quality assessment is based on the fruit’sinternal as well as external characteristics, with both methodsleading to the achievement of the same objectives with slight dif-ferences in system design and types of sensors embedded in thesystem to measure the characteristics. The basic contents of theinternal grading system designed to evaluate agricultural productsare shown in Fig. 3 (Zhao et al., 2009). The system is composed ofthe following items: A sample testing station, special sensor and aroller–conveyor feeding system which carries the product samplesto the sample housing as well as controls, separates and samplestheir classes after grading. A high-speed computer is utilized toprocess and analyze the sample’s signals using specific softwarein order to obtain the quality result and a data acquisition systemintermediates between the sensor and computer with digital signalprocessing (DSP).

2.2. Signal processing steps

The application of innovative signal processing techniques inagricultural product quality assessment is quite progressive andtimely. Owing to the fact that most fruits as well as vegetablesare readily perishable in the face of large-scale production, thequality assessment application must be performed as quickly aspossible and at a low cost. As such, chances for the signal process-ing society to donate to food assessment and other agriculturefunctions are numerous (Pearson et al., 2007). Such a techniquemay take the form of digital audio signal processing, digital controlengineering, speech processing, radar, communications and signalprocessing. The general steps involved in digital signal processingof agricultural internal grading systems are (i) data acquisition(sensor electronics), (ii) pre-processing (A/D converter), (iii) signalprocessing (single-board embedded DSP) and (iv) feature extrac-tion and classification.

Abdullah et al. (2006) reported that a portable electronic artifi-cial taste sensor using digital signal processing (DSP) technologies

would serve this purpose. Eight types of lipid membranes wereused for sensor construction in order to form the multichannelartificial taste-sensing equipment. The system was skilled in orderto detect Eurycoma longifolia Jack (ELJ) into four different concen-trations: 0.01%, 0.03%, 0.05% and 0.08%. More than 100 sampleswere used for the system test to determine which system was ableto classify the test mixtures correctly with more than 90%accuracy.

3. Methods and techniques

The internal grading system of agricultural products is a systemused to measure different types of signals of the fruit’s internalcharacteristics such as (Moisture, Sugar, Acid, Ripeness, etc.), usingdifferent types of sensors combined with specific methods andtechniques based on the fruit’s internal feature properties. In thispaper, the application of internal inspection system technologiesfor agricultural products is critically reviewed. The results of thestudy would be useful to agricultural engineers, manufacturingengineers, food engineers, and other researchers in the food andagriculture industries. Numerous reviews on agricultural internalgrading systems are addressed in this paper to support a numberof frontier studies conducted by previous researchers on the useof electromagnetic techniques to determine the moisture contentand dielectric properties of materials to measure the quality ofagricultural products such as those by Kaatze and Hübner (2010)and Soltani et al. (2011). A critical review of the measurementtechniques and applications of electrical properties for nondestruc-tive quality assessment and near-infrared spectroscopy (NIRS), aswell as the NIRS-advanced analytical tool for wheat breeding, trad-ing, and processing, were established by Jha et al. (2011) and Pojicand Mastilovic (2012). A study on the use of low-intensity ultra-sound in food technology was reported by Mulet et al. (1999) ina critical review. Zaporozhets and Krushinskaya (2002) analyzedthe potential use of radiography in postharvest to detect internalpests in deciduous tree fruits. Magnetic resonance and its agro-industrial applications were reviewed by Torres (2007). X-rayimaging methods for internal quality evaluation of agriculturalproduce were evaluated by Kotwaliwale et al. (2011). Qualityassessment of horticultural products by nuclear magnetic reso-nance (NMR) spectroscopy was re-examined by Hills and Clark(2003). A valuable review on the use of sensors for product charac-terization and their effect on the quality of specialty crops was con-ducted by Ruiz-Altisent et al. (2010). The use of ultrasound to

Table 1The advantage and disadvantage of internal grading system techniques used with agricultural crop application.

Technique Advantage Disadvantage Reference

X-ray and CT Nondestructive 3D imaging Limited resolution Kalender (2006)Calibration of gray levels requiredLarge (dm-scale) geological specimens cannot be penetrated bylow-energy X-rays

Little or no sample preparation requiredSpeed in extracting details and simplicity

Not all features have sufficiently large attenuation contrasts foruseful imaging

Digital display and storage and can be rapidly transferredbetween applications

Image artifacts (beam hardening) complicate data acquisitionand interpretation

Necessary for the quality of the images to be at least as good asthose produced in film centers; and image is post processed byusing different algorithms or filters Considerable computer resources required for visualization and

analysisIonizing radiation can cause tissue damage

Capacitanceandinductanceprobing

Robustness (capacity to resist mechanical vibrations andeventual mechanical shocks)

Further studies on dielectric properties are necessary to obtainsatisfactory results for sensing quality factors

Soltani et al.(2011)

High speed and resistant to poor environmental conditionsEasy to operate and low cost; used in precision agriculture

Electricalimpedance

Impedance properties have merits in the quality assessment offruits and vegetables, which make the replacement of currenttechniques by the EIS-based approach reasonable

Further exploration is important in acquiring more data on theEI characteristics of fruits and vegetables; research on newapproaches for the determination of their quality

(Liu, 2006)

A more precise measure of food quality which could be used tomonitor ripening changes in agricultural products

Microwave Safe and nondestructive compared with other internal fruitcontent measurement methods

Density fluctuations cause significant errors in internal fruitcontent determination

Trabelsi et al.(1998)

Successfully used in numerous industrial applications forinternal fruit content determination in different materials

Difficult to stabilize the density mechanically because particlesmove on a conveyor

MRI Has the potential to be performed in vivo Problem of acquiring useful in vivo images is caused bymovements of internal organs and muscles

Hart et al.(2003)Possible to produce high-resolution images of internal structure

in vivoOffers a real opportunity to view the internal structure of livingmaterials and to resample an individual numerous times overan extended time period

Image acquisition time is relatively longer than the frequencytime scale of internal movements; thus, the resulting images areblurred, rather similar to having an inappropriately slow shutterspeed in a conventional camera

Radiation Short processing time More expensive than techniques that rely on fossil fuels Alothman et al.(2009) andKimambo(2007)

Minor effect of irradiation on antioxidants in plant produce Has a small power density, thus requiring large areas to collectsignificant quantities of energyCauses minimal changes to the taste, appearance, texture, and

nutritional value of food Variable in time (night/day, the seasons, the clouds)Cannot be stored in its original formA safe, nondestructive technique that does not pollute the

environmentDoes not introduce more heat into the atmosphere

Ultrasonic A good option for nondestructive field measurements Difficulty in transmitting sufficient ultrasonic energy throughfruits and vegetables to obtain useful measurements because oftheir structure and air spaces

Abbott (1999)Higher speed over the air

Can only be used to determine firmness in some fruits, requiresa more powerful ultrasonic sourceLimited by the shapes of surfaces and the density or consistencyof the fruit

NIR Faster analysis, little or no operator involvement, and lowercosts

Called a secondary method wherein the sample used forcalibration and validation must also be analyzed by usinganother method

Roggo et al.(2007)

Environmental benefits, improved precision, and possibleautomation Considered as the primary method as well as the detection limit

CT = computed tomography, MRI = magnetic resonance imaging, NIR = near infra red.


detect defects in trees was investigated by Leininger et al. (2001). Areview of the theory, instrumentation, and applications of mag-neto-elastic resonance sensors was presented by Grimes et al.(2011). Finally, the advantages and disadvantages of internal grad-ing system techniques for agricultural crop application are summa-rized in Table 1. The information gathered would be helpful for thefurther commercialization and exploration of these technologieson a pilot scale in the food industry.

3.1. Fruit moisture measurements

The moisture content of agricultural products is a good classifi-cation indicator. This has been addressed by numerous researchersin their studies. A sensor for the measurement of the moisture con-tent of a medium was invented by Lock (2011). This sensor variesmedium conditions and the linearity of the response curve basedon the volumetric water content of the medium. The ZigBee wire-

less soil moisture sensor for vineyard management systems wasdesigned by Perera (2010). This sensor can be used to measure soilmoisture content. The effect of moisture content on the physicalproperties of soybean grains has been studied as well as their re-sponse under compressive load (Tavakoli et al., 2009). They usedfour stages of moisture content ranging from 6.92% to 21.19%and determined the average length, width, thickness, arithmeticand geometric mean diameter, surface area, thousand grains massand angle of repose where the samples moisture requirement con-tents were archived by increase the amount of distilled waterbased on the calculation of the Eq. (1).

Q ¼WiðMf �MiÞ100�Mf

ð1Þ

where Q is water’ mass, kg, Wi is sample’s initial mass in kg, Mi is thesample’s initial moisture content in d.b.% and Mf is the sample’s fi-nal moisture content in d.b.%.

Fig. 4. Open-ended coaxial sensor placed against the surface of the fruit mesocarp.(a) Fruit measurement (b) The PTFE stub of the SMA panel was machined flat to beused as the coaxial sensor (Abbas et al., 2005).


In addition, a study on the rapid determination of leaf watercontent by using visible (VIS)/NIR spectroscopy with wavelengthselection was conducted by Zhang et al. (2012). The results showthat a root mean square error of prediction (RMSEP) of 0.73% with25 variables was obtained for water content prediction by usingexternal validation. This finding could facilitate the developmentof a portable instrument for the synchronous, rapid, and non-destructive detection of water content and of other biochemicalparameters.

Similarly, the physical properties of various crops such asgroundnut kernel have been studied by Olajide and Igbeka(2003). The effects of moisture content on several physical proper-ties of lentil seed were examined by Amin et al. (2004). The resultsshow that the diameter, thickness, porosity, mass of 1000 seeds,and angle of repose linearly increased from 3.84 mm to 4.06 mm,2.18 mm to 2.48 mm, 34.48% to 37.00%, 20 g to 25.5 g, and 24.80�to 27.78�, respectively, with an increase in moisture content from10.33% to 21.00%,wheras bulk density and kernel density linearlydecreased from 832 kg/m3 to 768 kg/m3 and from 1270 kg/m3 to1212 kg/m3, respectively, under the same condition.

The physical properties of sweet corn seed were also analyzed.The results of the analysis show that: (1) 1000 seed mass increasedfrom 131.2 g to 145.5 g, and sphericity increased from 0.615 to0.635 with a moisture content increase from 11.54% d.b. to19.74% d.b.; (2) projected area increased from 59.72 mm2 to75.57 mm2, and porosity increased from 57.48% to 61.30%; (3) bulkdensity linearly decreased from 482.1 kg/m3 to 474.3 kg/m3; (4)true density increased from 1133.8 kg/m3 to 1225.5 kg/m3; (5) ter-minal velocity increased from 5.56 m s�1 to 5.79 m s�1; and (6) sta-tic coefficient of friction increased for all four surfaces: rubber(0.402–0.494), aluminum (0.321–0.441), stainless steel (0.267–0.401), and galvanized iron (0.364–0.477) (Coskun et al., 2006).The following results were obtained from the study of linseed. Asmoisture content increased from 8.25% d.b. to 22.25% d.b., bulkdensity decreased from 690.5 kg/m3 to 545 kg/m3. Meanwhile,the angle of repose, terminal velocity, and porosity were found toincrease from 21.591 to 26.851, 2.46 m/s1 to 3.82 m/s1, and31.64% to 46.59%, respectively (Selvi et al., 2006). In faba beangrain, bulk density was found to decrease from 419.59 kg/m3 to381.6 kg/m3. The static and dynamic coefficients of friction on var-ious surfaces linearly increased. The rupture force values rangedfrom 314.17 N to 185.10 N, 242.2 N to 205.56 N, and 551.43 N to548.75 N for the X-, Y-, and Z-axes, respectively. The rupture en-ergy values ranged from 203.83 N mm to 681.56 N mm,135.63 N mm to 651.03 N mm, and 217.93 N mm to 1090.6 N mmfor the X-, Y-, and Z-axes, respectively, as moisture content in-creased from 9.89% d.b. to 25.08% d.b. (Altuntas and Yıldız,2007). The physical properties of rough rice grain, jatropha seed,and karanja kernel changed based on the variation in moisture le-vel (Bamgboye and Adebayo, 2012; Garnayak et al., 2008; Pradhanet al., 2008; Varnamkhastia et al., 2008).

In order to study the moisture removal pattern inside a singlegrain of wheat (cultivar: A.C. Barrie) during drying, magnetic reso-nance imaging (MRI) was used to record MR images at equal timeintervals and moisture patterns were analyzed from the MR imagesof wheat kernels (Ghosh et al., 2006). The study demonstrates thatthe moisture loss from the seed parts differed significantly duringdrying and was dependent upon the grain components. Similarly,the use of magnetic resonance imaging (MRI) to examine waterdistribution and migration in single rice kernels during the tem-pering process. The MR images demonstrated that the moisturedistribution in the rice kernel is non-uniform and compartmental,which could be used as an efficient tool to examine the mecha-nisms of moisture migration within cereal grains (Hwang et al.,2009). The MRI of strawberry slices during osmotic dehydrationand air drying was investigated by Evans et al. (2002) to prove that

water diffusivity is sufficiently fast to replenish the water lost atthe surface, thereby maintaining molecular mobility throughoutthe slice.

Di-electric properties such as quasi-static capacitance, imped-ance, microwave, sub-millimeter wave reflection and transmissionas well as resonance methods. these di-electric properties wereused to obtain a comparatively uniform temperature allocationwithin and among the fruits during RF heating was investigatedby Ikediala et al. (2002) and demonstrated that a mortality rateof more than 99% of 200–400 codling moth larvae or 589 to 624eggs obtained at 50 �C during treatment between 7 and 10 min(heating time of 2–5 min and holding time of 5 min).

The utility of capacitance probes to continuously and accuratelymonitor soil water in drip irrigated melon production was exploredby McCann et al. (2007), who proved that irrigation quantity couldlikely be reduced without having an adverse effect on Yield, whichsuggests that growers in the region tend to apply more water thanmay be required as a form of risk avoidance. Among others, theYield of seedless melons per unit area of land ranged from about55–95 tones/ha, depending on the year and the irrigation rate.


Other applications include providing continuous recording for themonitoring of soil water content and allowing tropical fruit grow-ers to fine-tune their irrigation management strategy in south Flor-ida (Al-Yahyai et al., 2003). These researchers concluded thatmonitoring water use in different areas of the root zone can provethat the pre-set soil water depletion rate at which to irrigate mustbe related to plant vigor, growth and yield.

Electrical impedance has a good relation with agricultural cropquality estimation. The oil palm fruits’ permittivity and moistureare measured by using an open-ended coaxial sensor with a rela-tionship between the normalized admittance ~Y and reflection coef-ficient C expressed in the Eq. (2) and illustrated in Fig. 4 wasestablished by Abbas et al. (2005). The amount of moisture contentwas established by matching the values of permittivity from thequasi-static model with the permittivity of a dielectric mixturemodel. The moisture content values were obtained from the stan-dard oven drying method. Other researchers used electrical imped-ance spectroscopy to measure the impedance spectra ofagricultural crop slices during drying to correlate impedanceparameters to moisture content during different drying periods(Kumar et al., 2006; Mészáros et al., 2005; Mizukami et al., 2007;Nelson and Trabelsi, 2008, 2009). The investigation of dielectricsensing for fruit quality determination; dielectric spectroscopymeasurements on fruit, meat, and grain; the influence of watercontent on RF; as well as the microwave dielectric behavior of foodwere studied by Nelson et al. (2008), Nelson and Trabelsi (2008)and Nelson and Trabelsi (2009). They surmised that the dielectricbehavior of food materials is significantly affected by their watercontent.

~Y ¼ 1� C1þ C

� �ð2Þ

Moreover, the moisture content estimation in bread using the mul-ti-channel electrical impedance spectroscopy non-destructivemethod based on the rapid loss of freshness was studied by Bhattand Nagaraju (2009). A linear relationship was found between mea-sured impedance and residual moisture in crumb and crust duringstorage for 120 h for 5 days. This finding proves that the instrumentcan be used to monitor moisture migration in different bread prod-ucts during storage given the reproducibility and repeatability ofthe method. Moisture content measurement for small samples ofin-shell peanuts and individual dates by RF impedance methodwas performed by Kandala and Nelson (2007). Moisture contentwas predicted based on the capacitance and phase-angle measure-ments at three specific frequencies (1 MHz, 5 MHz, and 9 MHz). Anequation relating MC and empirically determined calibration con-stants would be useful in the drying, storing, marketing, and pro-cessing of peanuts with the use of such an instrument. Themeasurement of fresh tea leaf growth based on its moisture contentby using EIS was conducted by Mizukami et al. (2007). They con-cluded that relaxation time aids in the estimation of the growthof tea leaves. Pulsed electric fields, combined with the impregnationof vacuum with trehalose, was found to improve the freezing toler-ance of spinach leaves, as demonstrated by Phoon et al. (2008). Theresults provide evidence that the combination of electric fields andvacuum impregnation can significantly enhance the freezing toler-ance of spinach leaves.

A comparison study of methods to determine moisture in foodwas investigated by El-Sayd and Makawy (2010) and demon-strated that microwave frequencies are better than using lowerfrequencies. Additionally, microwave frequencies are not affectedby variations in ionic conductivity, which is responsible for errorsin moisture measurement at low frequencies. Hence, the micro-wave technique has found many applications in agriculture likethe determination of oil palm fruit ripeness. The use of a low-cost

coaxial moisture sensor to determine a moisture content from 30%to 80% weight of the fruits suggests that the coaxial sensor is suit-able for determining fruit quality based solely on the measuredphase of the reflection coefficient u for medium fruits up to5 GHz (Yeow et al., 2010). The results of a study that evaluatedmaturity in durian show that microwave moisture sensing can pro-vide an accurate measurement of moisture content inside a durianat 3 GHz with the capability to predict the day-after postharvest(Rutpralom et al., 2002).

Additionally, radiation measurements are one of the most fa-mous methods used to estimate agricultural crop quality basedon moisture. A novel NMR imaging technique was modified toinvestigate the role of glass transition on Fickian and non-Fickianmodes of moisture transport in continuous and intermittent dryingof pasta and concludes that the time step size and drying air con-ditions need to be carefully controlled to optimize intermittentdrying (Xing et al., 2007). Cousens et al. (2010) concluded thatthe fruit modifies the seed environment as external conditionschange between wet and dry with major influences such as (a)the physical restriction of imbibition and germination and (b) therelease and re-imposition of dormancy within the seed. This find-ing was based on a study of the role of the persistent fruit wall inseed water regulation in Aphanus raphanistrum by using X-ray andweight measurement. The three-dimensional (3D) gas exchangepathways in pome fruit characterized by synchrotron X-ray com-puted tomography was analyzed by Verboven et al. (2008). Theyconcluded that jointed tomography and internal gas study duringgrowth are needed to explore sympathetic void formation in fruitsfurther.

Chen-Mayer and Tosh (2007) showed that the high-resolutionultrasonic thermometer is one of the important methods used tomeasure absorbed dose in water calorimeters. The results of thelong-term prediction of Zhonghua kiwifruit dry matter by NIRspectroscopy show that the RMSEP and r were 0.53% and 0.90,respectively. The change in characteristic wavelength regions re-sulted from the chemical conversion of organic compounds in-cluded in the dry matter at different storage periods of kiwifruits.Moreover, NIR spectroscopy of unripe kiwifruits was found to becapable of predicting the dry matter (Lu et al., 2010).

Magnetic resonance imaging (MRI) and Computed Tomography(CT) are vastly utilized with agricultural applications based onmoisture measurements. The results show that the MRI techniquecan possibly analyze water transport phenomena through theinterface. This finding could explain the performance of differentproducts and could also be useful in the development of new prod-ucts (Ekstedt et al., 2007). Kikuchi et al. (2006) studied the applica-tion of MRI in determining the MR parameters of water uptake indry beans, which observed by using micro MRI to elucidate thechannel of water entry, the manner of water delivery, and the tim-ing of swelling of the seeds. A study of non-intrusive changes ofvivo water content with the dissimilar parts of the leaves through-out a drought strain by a useful tool such as through MRI tech-niques was elucidated upon by Sardans et al. (2010). The resultsshow that MRI is a useful tool in non-intrusively followingin vivo water content changes in different parts of the leaves dur-ing drought stress.

3.2. Fruit sugar measurements

As per the aforementioned, sugar content can be used as a ma-trix for the evaluation of fruit quality and maturity (Lin and Ying,2009). This has been demonstrated in various research efforts.The sugar content of apples was predicted by using Kernel partialleast squares regression on wavelet-transformed NIR spectra (Nic-olaï et al., 2007). NIR spectroscopy (700–1100 nm) was performedon watermelons to verify the correlation coefficient (r) and the


standard error of prediction values, which are found to be 0.81 and0.42 Brix%, respectively (Abebe, 2006).

The near-infrared spectrophotometer ‘NIR’ technique has signif-icant application in internal grading systems based on contentassessment. A non-destructive Long-term prediction of Zhonghuakiwifruit dry matter was investigated, that way was based on thenear infrared spectroscopy (NIRS) techniques which is found tobe competent of estimating root mean square error of predictionand r were 0.53% and 0.90, respectively. This study established thatNIRS is proper technique for predicting the dry matter of unripekiwifruits (Lu et al., 2010). Similarly, (Kurz et al., 2009) investi-gated the NIR spectroscopy technique with fiber optics in interac-tion form and an analytical process using Fourier transform nearinfrared (FT-NIR) spectroscopy and chemo-metrics with multivar-iate techniques with the purpose of sugar content level determina-tion in undamaged peaches, apricots and pumpkins. Meanwhile,the combination of Infrared Spectroscopy and NMR spectroscopywith Principal Component Analysis (PCA) was used for the fastdetermination of the ripeness stage of strawberries by using theconcentrations of three small sugars (a-glucose, b-glucose and su-crose) in order to evaluate the NMR spectral characteristics at eachripeness step (Kwak et al., 2007). The studies point out the concen-tration of sugar increased from early to late growth stages. Both IRand NMR spectroscopy are important to clarify the metabolic sig-natures used for the determination of maturity stage. IR spectros-copy id more suitable when rapid, high-throughput analysis isnecessary.

In addition, the three non-destructive techniques namely; a NIRspectrophotometer, a machine vision system and an electronicnose system were used together for quality inspection of ‘‘Fuji’’ ap-ples. The purpose was to obtain the advantages of three sensors fora sugar content measurement (local measurement) and assess-ment the other fruit physical properties (color, size, shape and ar-oma) as global measurement in order to combine those types ofmeasurements for a highly accurate quality assessment. Xiaoboand Jiewen (2005) reported that the classification error rate for su-gar content assessment drops from approximately 17% when usingonly NIR spectra to approximately 6% when the three sensors arecombined through ANN. The rapid detection of sugar content infruit vinegar by using NIR spectroscopy was investigated by Wanget al. (2008). The results indicate that the correlation coefficient (r)and RMSEP for the prediction of sugar content are 0.9939 and0.363, respectively.

As clearly detailed in the various studies that deal with thisproblem, sugar content plays a pivotal role in fruit quality assess-ment. The effect of pre and post harvest treatments on the sugarcontent changes in tomatoes has been studied in Meaza et al.(2007) and Melkamu et al. (2008). The result showed that theuse of ComCat� and its combination provided the uppermost totalyield 58.53 tha-1 and 55.77tha-1 of which 94% and 93% were mar-ketable and total yield, respectively. The researchers generallyfound that maintaining higher reducing sugar and total sugar intomatoes is a benefit of the combined effect of preharvest treat-ment and evaporative cooled storage. Seed vigor assessmentrefinement for super sweet and sugar-enhanced sweet corn wasdescribed by Zhao et al. (2007). A strong model was created forthe prediction of field emergence and for the forecasting of fieldemergence percentage (FEP) and field emergence time (FET) in su-gar-enhanced sweet corn by combining with DA and multipleregression equations: y = 45.849 + 92.991� 1(DA)� 1.292� 2(EC)�0.129 � 3(PPGP) � 0.103 � 4(SS); and y = 22.651 � 17.276 � 1(DA)� 0.028 � 2(AAAAGP) � 0.111 � 3(CGP), respectively. Whereas,based on the sugar and acid contents during shelf-life, a non-destructive judgment of nectarine ripeness by time-resolvedreflectance spectroscopy was studied. Therefore, the study con-cluded that individual fruits can be selected and sorted according

to fruit quality by using TRS to measure la at harvest time (Sanuet al., 2006).

Electrical impedance spectroscopy based on sugar content hasbeen applied in agricultural crop studies. Diezma-Iglesias et al.(2004) studied the watermelon ripeness assessment in the fieldvia acoustic impulse impedance techniques, wherein good anddefective seedless watermelons were tested with the acoustic de-vice. Spectral parameters were examined as potential non-destruc-tive predictors of internal disorders. The result shows that theacoustic parameters have the best ability of to detect internal dis-orders. Furthermore, the investigation of dielectric sensing for fruitquality determination was performed by Nelson et al. (2008) in or-der to examine the permittivity of honeydew melons and water-melons grown to provide a range of maturities. Good correlationswere obtained between the permittivity and soluble solid content(sweetness) of edible tissues. However, further research is neededto determine the potential for sensing fresh fruit quality basedon dielectric properties.

The agricultural fruit quality estimation using microwave imag-ing was widely used by different researchers worldwide, the devel-opment of nondestructive imaging of the fruit sugar distribution byapplying of a chirp pulse microwave computed tomography (CP-MCT) was carried out by Baki et al. (2010) and Watanabe et al.(2005). They confirmed that the sugar distribution inside the Japa-nese pear varies according to harvest time. Similarly, the changesand quality of ripening tomato fruits effected by UV-B radiationthrough both ethylene-dependent and independent mechanismsduring ripening were assessed by Becatti et al. (2009). The effectof ionizing radiation on fresh-cut fruits and vegetables based onfuran formation was studied by Fan and Sokorai (2008), The resultshows that radiation resistance varies among vegetables. Broccoli,endive, and red cabbage have higher radiation resistance thancilantro, green onion, and carrot. Radiation resistance is not relatedto endogenous antioxidant capacity or to phenolic content. Theapplications of a non-destructive ultrasonic system for fruit sugarcontent evaluations are used widely in agricultural crop quality re-search. A system with pulse-echo (PE) or transmission-through(TT) mode detects the sugar content and viscosity of reconstitutedorange juice by using the responsive velocity of ultrasound. Powerattenuation shows that the velocity exhibits a high linear correla-tion with Brix in orange juice, with r = 0.994 in PE mode. The deter-mination of the optimum conditions for sucrose production usingultrasonic treatment were studied by Kuo et al. (2008) and Kwan(2009). The researchers concluded that the highest sucrose produc-tion was 68.63% of the original amount at conditions of 60% w/vcoconut sugar concentration at 68 kHz ultrasonic treatment.

In addition, the changes of postharvest structure for Haywardkiwifruit based on sugar using magnetic resonance imaging(MRI) were investigated. The study shows that MRI is a useful toolfor identifying the slightest texture changes linked with watermobility. Water organization and mobility are more importantparameters than water content, especially for the maturity process.Minimal variation in vapor pressure by water loss and tempera-ture, textural changes, and kiwifruit softening for this organizationare altered (Taglienti et al., 2009). Wall (2008) reported that theirradiation treatment of dragon fruit at doses of 800 Gy or lesscan ensure visual and compositional quality as well as providequarantine security on the postharvest quality of dragon fruit afterX-ray irradiation quarantine treatment. Associations of dietary su-gar and glycemic index with adiposity and insulin dynamics inoverweight Latino youth that were determined by using X-raywere discussed by Davis et al. (2007). Regression analyses showedthat the total sugar intake explained an additional 3.4%, 4.6%, and2.4% of the BMI variance as well as an additional 5.6% and 4.8%of the SI variance and of the disposition index (P < 0.05),respectively, after the covariates were controlled. Nondestructive


measurement of the sugar content of apple by using the hyper-spectral imaging technique was performed. The hyperspectralimaging technique is potentially useful in assessing the sugar con-tent of apple when the correlation coefficient (r) between thehyperspectral imaging prediction results and reference measure-ment results is equal to 0.90749 (Zhao et al., 2009).

Fig. 5. Ultrasonic measurement assembly (Sarangi, 2007).

3.3. Fruit acid measurements

The fruit acid ratio is another integral determinant of fruit qual-ity. Researchers have used various techniques with various fruitacids in order to investigate which method may be best suitedfor a rapid and reliable examination of a huge number of samples.Most recently, (Váchová et al., 2009) determined the concentrationof sugar and acid in the fruits by using HPLC, RI detector as well asisotachophoresis in order to assess the best rate of acid and sweet-ness taste for lemons. They reported that the best-tasting lemondrops contain 11 g/kg of citric acid and 691 g/kg sweeteners. Thisfinding is related to the sweet potency of sucrose, which explainsthe assessors’ preference for lemon drops with well-balancedacidic and sweet taste. In addition, a similar study on the oil acidratio of vegetable oil has also been carried out. Fatty acid combina-tion and the behavior of pear seed oils, which indicated that thespecies did not exhibit any important difference in terms of phys-ical and chemical parameters. The main fatty acids of prickly pearseed oil were C16:0, C18:0, C18:1, and C18:2. The content of unsat-urated fatty acids was high, with an excellent level of linoleic acid(up to 70%) at 88.5% and 88.0% for O. ficus indica and O. stricta,respectively. A significant two-way interaction, especially regard-ing fruit and oil yield, may imply that the use of 100% etc.(T100), along with F3, is useful for higher fruit and oil yield. Basedon the oil characteristic determination of olive in dissimilar irriga-tion and fertilization regimes that has been investigated by Enno-uri et al. (2005) and Toplu et al. (2009). A method to determinepear sugar and acid content in fruit juices by using the SPE-car-tridge module Syncore� Analyst was introduced by Kolbeneret al. (2006). NIR spectroscopy on aqueous citric, tartaric, malice,and oxalic solutions was performed through quantitative analysisby selecting a set of wavelengths that can best be used to measurethe pH of the solutions. This analysis was conducted by Omar et al.(2012), with the critical selection of important wavelengths for pHlocated at 918 nm to 925 nm and 990 nm to 996 nm, whereas thatfor water was at 975 nm.

Furthermore, the widespread use of ascorbic acid (vitamin C) inmedical fraternity as well as in the food industry is due to the vari-ety of uses of this substance. Pisoschi et al. (2008) and Pisoschiet al. (2011) investigated the ascorbic acid of fruit and vegetablejuices determination based on flow injection with immobilizedascorbate oxidase. An accuracy of 1% at 100 mg/ml1 was illustratedfor various juice samples. This value is also suitable for clinicalanalysis and for ascorbic acid determination in commercial fruitjuice samples by using a cyclic voltammeter with a degree ofrecovery between 94.35% and 104%. Good agreement with the re-sults was obtained. Rodrigo et al. (2003) studied the characteriza-tion of a novel mutant called Pinalate, which was derived fromorange. They reported that, given the abnormal fruit-specific carot-enoid complement and abscisic acid (ABA) deficiency, Pinalate mayconstitute an outstanding system for the study of carotenogenesisin citrus and the involvement of ABA in fruit maturation and stressresponses. The effect of gibberellic acid (GA3) on fruit cracking wasalso studied. The quality of Bing and Sam sweet cherries was eval-uated by Cline and Trought (2007). They reported that the repeatedfoliar applications at 10 mg/l1 or singular foliar applications at40 mg/l1 of GA3 increased fruit cracking and fruit firmness, but de-layed fruit color development.

As a variant of the aforementioned acid ratio based qualityassessment, Wolf and Zainal (2002) studied the content of methyl-seleno-amino acid for food materials based on stable isotope dilu-tion mass spectrometry. They found that two materials, wheatgluten reference material with 64% methylselenium and commer-cial selenium yeast tablets with 73% methylselenium, are goodcandidates for further study and characterization as referencematerials for determining this important food component. A com-parative study of amino acid quantity in leaf take out by gas offlight-mass spectrometry and liquid chromatography by fluores-cence discovery has been described by Noctor et al. (2007). The re-sults show that the gas chromatography–time of flight-massspectrometry (GC–TOF-MS) analysis of Arabidopsis leaves usingthe present protocol can be used for the absolute quantificationof 4–7 amino acids and for the accurate relative quantification of8–11 amino acids. However, the process provides a more limitedquantification for five compounds of this class. The improvementof pectin acid extraction from passion fruit peel was performedby using response surface methodology (RSM). (Kliemann et al.,2009) described that the most excellent pectin yield with a rateof 70% was obtained for citric acid when the extraction conditionswere optimized at pH 1.0, 80 �C, and 10 min using RSM. Similarly,an internal quality evaluation (acid content) of peaches showedthat CT number, moisture content, and titratable acidity signifi-cantly decreased with postharvest ripening time, whereas pH andsoluble solids increased with postharvest ripening time. ‘‘Afourer’’mandarin fruit showed a continuous increase in the specific activ-ity (%) of the enzyme during storage. The suggestion that shellaccoating is more viable than Semperfresh and CMC coatings interms of reducing respiration rate and weight loss and in maintain-ing the quality of pears was based on the study of Huanghua pearsthat was conducted by using X-ray CT. The effects of rootstock anddifferent kinds of coatings during storage have been demonstratedby El-hilali et al. (2003) and Zhou et al. (2008). In a separate study,Al-Shahib and Marshall (2003) investigated the internal contents(sugars, fatty acid, salts, minerals, protein, vitamins, fibers, fleshof dates, oil and seed contents) of date palm fruit to increase itsuniversal acceptance in the future, given that the total world ex-port of dates increased by 1.71% in over 40 years. Dates may beconsidered an almost ideal food that provides a wide range ofessential nutrients and potential health benefits.

On the other hand, capacitance and ultrasound are also utilizedfor fruit acid measurement. Capacitance and ultrasonic measure-ments were used for oil debris detection as illustrated in Fig. 5by Sarangi (2007). In the ultrasonic measurement method, thechange in energy of ultrasonic waves was used as an indicator tothe oil wreckage has a higher range. The change in the maximumreflection at resonant frequency of a series LC in a capacitancemethod circuit was estimated as oil debris having lower range of

Fig. 6. Electrical impedance measurement setup. A four-electrode measurement method was used (Fang et al., 2007).


size, which both of the methods successfully assess the wreckageof oil. Also, the development of a comprehensive procedure to de-tect debris and analyze the physical parameters associated withlubricating oil degradation using ultrasound and capacitance basedmeasurements was reported by Appleby (2010). He concluded thatthe system is capable of analyzing critical oil properties. Izadifar(2001) established that ultrasonic pretreatment and dielectricstudies assure the possibility of efficient extraction of phenoliccompounds from dried distillers’ grain (DDG) by applying radiofre-quency (RF)-assisted extraction methods for phenolic compoundsfrom DDG.

Electrical impedance is one of the most important methodsused for fruit acid estimation and measurements. Repo et al.(2004) reported that, the EIS properties of the leaves changed sig-nificantly during the growing season when new leaves wereexpanding. As shown in Fig. 6, Fang et al. (2007) comprehensivelyinvestigated the use of electrical impedance spectroscopy (EIS) todistinguish the electrical properties of plant tissue. The possibleconnections between electrical impedance and the main parame-ters of fruit taste were recognized and four apple assortments havebeen divided into three groups namely; low-acid assortment, high-acid assortment and medium-acid assortment. They concludedthat the EI approach offers a new method for apple quality assess-ment that can replace the traditional SSC and acidity measure-ments to quantify customers’ requirements when the given levelsof SSC and TA from the observed varieties are satisfactory.

The selection of bacteria using an electrical impedance mea-surement method with high metabolic activity for the treatmentof high potato industry fed by sewage was investigated by Lasikand Nowak (2010). The evaluation was performed in two ways.They are (i) the analysis of electrical impedance changes causedby bacterial metabolism during bioremediation process, and (ii)the reduction of chemical oxygen demand (COD). The result showsa significantly higher (p < 0.05) metabolic activity of bacteria and alinear correlation (r = 0.89) found among wastewater COD reduc-tions. The values of the maximal impedance change rate (Imax) en-able the use of the EI method and the proposed parameter for

easier and more rapid evaluation. In another study the coactionsbetween ethylene and auxin signaling in order to penetration to-mato root in soil requires has been reported (Santisree et al.,2011). The results indicate that, a coaction between ethylene andauxin is required for root penetration into the soil during tomatoseed germination.

The application of continuous microwave processing to acidi-fied vegetable products could reduce energy usage and water con-sumption, and thereby improve the sustainability of acidifiedvegetable production as documented by Koskiniemi (2010). Thestudy was aimed at developing packaged acidified vegetables suchas broccoli, red bell pepper and sweet potato to improve the levelsof beneficial phyto-nutrients compared to traditional pickledcucumbers. New approaches wherein heating patterns can bedetermined using chemical marker (M-2) yield are mathematicallyexpressed in Eq. (3). The heating process and computer vision weredeveloped for packaged foods to demonstrate that computer visionin combination with chemical marker M-2 and other accessoriescan be efficiently used as a fast, accurate and cost effective instru-ment to indicate the location of cold and hot spots after microwavesterilization (Pandit et al., 2007). Furthermore, the effect of micro-wave drying on spinach characteristics was investigated by Ozkanet al. (2007). The result shows that the best quality inspectionbased on color and ascorbic acid standards were acquired in thedrying period with a 750 W microwave power for 350 s, which car-ried out the least energy necessity for drying which was only0.12 kW h.

CðtÞ ¼ C1 � ðC1 � C0Þ expZ t

0�k0 exp � Ea

R1

TðtÞ �1T0

� �� dt

� �

ð3Þ

where C(t) is marker yield at any time, C1 is marker yield at satura-tion, Ea is energy of activation, R is molar gas constant, T(t) is re-corded temperature–time history at the measured point, T0 isreference temperature. Initial marker yield before heating, C0, wasdetermined as zero for mashed potato sample with 1.5% D-ribose.


Additionally, a microwave-vapor heat treatment (MW-VHT) hasbeen developed for mangoes in order to disinfest it from fruit fly orthe Bactrocera dorsalis. Meanwhile, Varith et al. (2007) investi-gated MW-VHT and reported that this equipment gave less heatdamage of mangoes than the other conventional vapor heat treat-ments (VHT). It also reduced the processing time by over 90%through the preheating period and maintained correspondent ormore lethality of oriental fruit fly eggs than the VHT method.

The effect of gamma-irradiation on palm oil has been investi-gated by Endinkeau and Woodward (1989). Irradiation doses(0.1–1 MGY) caused severe destruction of unsaturated fatty acidsbut had little effect on saturated fatty acids. The result indicatesthat gamma radiation may be used for the preservation but notfor the sterilization of palm fruits. The drying and quality charac-teristics of banana slices processed with a sequential infrared radi-ation and freeze-drying (SIRFD) method were studied by Pan et al.(2008). They investigated the application of the SIRFD method fordrying banana slices and for quality distinctiveness. They con-cluded that the SIRFD method can be used to make very crispy ba-nana chips and that additional acid dipping improves product colorand decreases the required freeze-drying time.

The use of the ultrasonic wave’s technology has been widelyused in food industry (Tran and Le, 2011). The Pectinex Ultra SP-L was used in pineapple mash treatment and juice processing withextraction yield increase of up to 5.6% by the sonicated pectinasecompared with the unsonicated enzyme (Tran and Le, 2011). Phe-nolic compounds extraction from strawberries prior to liquid chro-matographic separation using ultrasound-assisted was carried outby Herrera and Castro (2005). Photodiode array ultraviolet detec-tion and some of the other industrial applications of ultrasoundsuch as texture, viscosity, concentration measurements and com-position determination of agricultural crop has been widely inves-tigated by Ulusoy et al. (2007).

Fruit acid is one of the most important parameters used for fruitquality assessment. A lot of research is being conducted to investi-gate non-destructive processes such as nuclear magnetic reso-nance (NMR) and computed tomography (CT) for qualitydetermination of fruits based on ascorbic fruit acid. Carbonateinterlayered hydrotalcite-enhanced peroxynitrous acid chemilu-minescence for high-selectivity sensing of ascorbic acid was de-scribed by Wang et al. (2012). The system was effectively appliedto determine ascorbic acid in commercial liquid fruit juices withaccuracy from 97% to 107%. The system can facilitate furtherunderstanding of the unique properties of LDHs-catalyzed CL andthus has possible applications in numerous fields such as lumines-cence devices, bioanalysis, and labeling probes. Mealiness assess-ment in apples and peaches by using MRI techniques wasconducted by Barreiro et al. (2000). The results were summarizedas follows: (1) The association between internal breakdown andmealiness has the same histogram shape, and all internal break-down fruits are recognized as mealy through a confined compres-sion test; and (2) MRI techniques can be used to distinguishbetween woolly and non-woolly peach fruits. Nondestructivetomographic techniques such as X-ray CT imaging and MRI wereused in a study on the growth of core breakdown disorder in pearsby Lammertyn et al. (2003). The result shows that MRI is the mostsuitable technique for studying the improvement of core break-down disorder during postharvest storage.

Good linearity and sensitivity were recognized based on time-determined analysis and calibration tests with analytical accuracyof 98% to 102%. This finding was acquired through the study of tincontent determination in canned fruits and vegetables by using hy-dride generation inductively coupled plasma optical emissionspectrometry (Roncevic et al., 2012), The nutritional value of or-ganic acid lime juice (Citrus latifolia T. cv. Tahiti) was investigatedby Rangel and Carvalho (2011). The results show only a few nutri-

tional differences between organic and conventional acid limejuices in some constituents. Therefore, fruit juice from biodynamiccrops is an excellent option because it is free from pesticides andother agents that can negatively affect human health. A recentstudy on the visualization of intracellular ice crystal formation byusing X-ray microcomputed tomography based on the total pheno-lic (TP) and ascorbic acid of fresh and freeze-dried strawberry sam-ples was conducted by Zaid (2010). The result shows that theaverage TP content of frozen, freeze-dried, and air-dried strawber-ries are 270.5 mg/100 g, 231.0 mg/100 g, and 28.7 mg/100 g offresh weight, respectively.

3.4. Fruit ripeness measurements

Fruit-ripeness determination research is increasingly gainingprominence in the food industry. The market quality of agriculturalcrop and industrial food products can be estimated based on theripeness of the fruit. Computer vision for internal inspection is a ro-bot controlled fruit-ripeness determination method with the aid ofparticular sensors based on the internal properties of the fruit to betested. Nowadays, the application of the electronic nose system inagricultural product ripeness has significantly increased. Thedevelopment of the electronic nose system usually comprises anarray of semiconductor gas sensors as well as data acquisitionand analysis components. Such a system was used to inspect Haru-manis mango in three way classification corresponding to differentstates of fruit’s ripeness (Salim et al., 2005). In their study, thiselectronic nose system was proven effective for determining fruitripeness, and each stage of maturity of mango gives specific infor-mation such as a different pattern or fingerprint in the sensor ar-ray. Principal component analysis (PCA) is then used to definethree distinct regions according to the state of ripeness of theHarumanis mango. Once the PCA is completed, artificial neural net-work (ANN) is then trained to classify the data into the observedthree stages of ripeness. Similarly, (Banerjee(Roy) et al., 2012) useda combined electronic nose and electronic tongue for the classifica-tion rates improve of non-destructive of tea quality evaluation, asillustrated in Fig. 7. The results show that the classification accu-racy rates increases up to 93%, whereas with the independent sys-tems, the classification rate obtained is 83–84% with electronicnose and 85–86% with electronic tongue. The capability of non-destructive system to evaluation of apple maturity by using multi-variate analysis of variance (MANOVA) of the electronic nose (EN)sensor integrated with discriminate analysis (DA) showed theirefficiency to categorize Gala apples into the three maturity groupswith classification accuracy up to 83% (Pathange et al., 2006).

Additionally, Near-Infrared (NIR) spectroscopy has also beenemployed for the non-invasive assessment of intact fruit. (Chenand Han, 2012) investigated the application of NIR spectroscopyfor the determination of the soluble solid content of the ‘‘Qinmei’’kiwifruit by using partial least squares. A significant linear correla-tion was found between NIR spectroscopy and kiwifruit soluble so-lid content, where the determination coefficient r was 93.65%, andthe standard deviation of the root mean square error of predictionwas 0.656 �Brix. The nondestructive identification of tea (Camelliasinensis L.) varieties was investigated by Chen et al. (2008) by usingFT-NIR spectroscopy and pattern recognition. FT-NIR spectroscopytechnology with an ANN pattern recognition method achieved a100% accuracy rate for identifying tea varieties. The feasibility ofportable NIR spectroscopy technology for the determination of oiland moisture content in intact olive fruits was studied by Cayuelaand Camino (2010) and Gracia and León (2011), and the resultssupport the use of portable NIR spectroscopy to monitor olive fruitmaturity and to determine the best harvesting date based on oiland moisture content. In addition, nondestructive measurementof the moisture and soluble solid content of the Mazafati date fruit

Fig. 7. Block diagram for electronic tongue system for black tea analysis (Banerjee(Roy) et al., 2012).

Fig. 8. Color chart of banana fruits in various stages (Soltani et al., 2010).


by using NIR spectroscopy yielded the relative residual predictivedeviation (RPD) values of 7.1 and 4.8, respectively, and yieldedthe coefficient of determination (r2) values of 0.980 and 0.966,respectively. Thus, NIR spectroscopy is the recommended methodfor Mazafati date maturity assessment (Mireei et al., 2010). Cayu-ela and Camino (2010) directly measured the intact olive fruit

quality prediction parameters by using VIS/NIR spectroscopy andfound that the valuable estimation of the olive quality consider-ation analyzed during the RPD yielded ratios of 2.51–3.18. In a sim-ilar research that was conducted recently, Puangsombut et al.(2012) reported that the result of the evaluation of the internalquality of fresh-cut pomelo by using VIS/NIR transmittance

Fig. 9. Side view of sensor in a voltage divider setup. A banana is hung between thedriving and sensing system (Soltani et al., 2010).


indicated that VIS/NIR spectrophotometry with the support of thepreprocessing techniques is ideal for predicting the soluble solidcontent and TA of fresh-cut Kao Numpung pomelo.

MRI analysis by using the sensory perception and human per-ception and evaluation on a piece of the interior potato was provenaccurate and suitable for implementation in an online fruit sortingsystem and also using non-destructive impact testing to sort twovarieties of apples and pears. Thus, the sensory and the com-puter-assisted image analyses were capable of distinguishing be-tween varieties as well as storage times, whereas the sensoryimage analysis was easier to interpret and was better at distin-guishing between varieties than the computer-assisted imageanalysis (Jaren and Garcia-Pardo, 2002; Martens et al., 2002).

The quality assessment of banana fruit during the ripeningphase using remote sensing capacity was studied by Soltani et al.(2010) in order to develop fast and non-invasive way to controltheir maturity assessment (Fig. 8). The capacitance sensing system(Fig. 9) was capable of classifying the banana fruits during the rip-ening period and of assessing changes based on the quality param-eters, as the linear regression frequency value of 1 MHz offers asatisfactory correlation for both SSC and firmness with relative per-mittivity, which was selected for the development of the sensingsystem. Furthermore, electrical impedance is one of the attractivemethods used for fruit-ripeness quality estimation. Banana matu-rity was investigated based on EIS by Liu et al. (2008). The respira-tion climate during the ripening period of the banana was directlyfounded on the observed change in the EI. The nondestructiveimpedance spectroscopy technique aided by a two-terminal probeand an accurate LCR meter was used to assess the quality of fruits,and the result indicates that effective resistance can be used to dis-tinguish between raw and ripe fruits at a frequency range of 1 kHzto 6 kHz (Rehman et al., 2011). In addition, EIS analysis was used toinvestigate the effects of drying and freezing–thawing treatmentson the impedance characteristics of eggplant pulp. The membranesof the cells with dielectric properties in the tissue were signifi-cantly damaged during the freezing process, which was consideredthe main reason for post-thawing deterioration in the quality attri-butes of frozen products (Wu et al., 2008) as well as the investiga-tion of dielectric sensing for fruit quality determination forhoneydew melons, watermelons, and apples was conducted byusing an open-ended coaxial-line probe and an impedance ana-lyzer at frequencies from 10 MHz to 1.8 GHz (Nelson et al.,2008). Good correlations were obtained between the permittivityand soluble solid content (sweetness) of the edible tissue.

In addition, Peichl et al. (2007) provided a brief introduction tothe physical background of the microwave radiometry and mostlyconsidered imaging principles of the agricultural crop. The blacknet always exhibited a greater impact than the crystal net, result-

ing in a reduction of fruit color, soluble solid content, and sunburnas well as causing a subsequent delay in maturity. Thus, the use ofcrystal nets is advisable in warm areas with poorly colored or med-ium-colored cultivars based on the study of the impact of anti-Hailnets to protect the fruit, radiation, quality, temperature and profit-ability of apples was done by Iglesias and Alegre (2006). The appli-cation of ultrasound for fruit ripeness quality inspection based onfirmness was studied by Flitsanov et al. (2000), where the statisti-cal analysis showed that there is a good relationship between thebeam and reduce ultrasound. Measurements can be used ultra-sound as a method of nondestructive control of avocado maturity.

Magnetic resonance image and computed tomography (CT)have been widely used in the task of fruit quality inspection (Ab-bott, 1999; Butz et al., 2005). In order to assess the interior ofthe potato, sensory analysis of magnetic resonance imaging andimage analysis using visualization and human perception wasstudied by Martens et al. (2002). Sensory image analysis wasstrongly recommended over computer-assisted image analysisfor better and easier discrimination between varieties. In contrast,many studies reported the performance comparison of the MRI andX-ray CT. MRI, which has the advantage of a short processing time,was reported to yield better results in terms of the development ofcore breakdown compared with X-ray CT, which has the advantageof low cost (Yacob et al., 2005). Conversely, Lammertyn et al.(2003) concluded in an MRI and X-ray CT comparison study of spa-tial distribution of core breakdown in ‘‘Conference’’ pears appliedin postharvest nondestructive detection that X-ray can be used innon-destructive detection because it is more convenient and lesscostly compared with MRI. Two types of fast MRI sequences wereinvestigated, namely, a gradient echo and a spiral–radial (Barreiroet al., 2008). The radial–spiral sequence achieved an accuracy of100%, which was higher than the 98.7% accuracy achieved by gra-dient echo images. In addition, the effect of X-ray irradiation on thephysical and chemical quality of the American red globe grape wasinvestigated by Kang et al. (2012) to prove that X-ray irradiation ofup to 1.0 kGy has no negative effect on the physical and chemicalquality of fresh grape. Thus, irradiation is considered as a potentialquarantine treatment for fresh grapes as well as for postharvestquality and ripening of Dwarf Brazilian bananas (Musa sp.) afterX-ray irradiation quarantine treatment, as discussed by Wall(2007). The treatment of fruit from the proximal half of bunchesat doses 6600 Gy is a viable assessment of visual quality and canprovide quarantine security for Dwarf Brazilian bananas.

3.5. Fruit damage measurements

Internal fruit damage is one of the most critical problems affect-ing the quality of agricultural products. Many different agriculturalresearch centers around the world concentrate on the develop-ment of internal grading systems for agricultural crop in order toaddress this phenomenon such as peaches damage (Fig. 10) (Yanget al., 2006). The specific methods and techniques used in the var-ious research efforts are a function of the kind and variety of fruitand their damage type. Xing and Guyer (2008) devised a mecha-nism to detect internal insect invasion to tart cherry using trans-mittance spectroscopy. The sample remains intact, as well ascherries full of different levels of damage. Depending on thearrangement of the layers in the samples is infected or contami-nated, and the accuracy of the total rating of 82–87%. These resultsshow that the spectral analysis of the permeability has a strong po-tential for the detection of pests within the internal fruit tart cher-ries as shown by accuracy percentage. Although at the researchstage, The X-ray of interest to a great deal of research, particularlyin the kernels of grain with the summary that the uninfested andinfested wheat kernels were correctly classified based on larvalstages with more than 95% accuracy for all the classifiers.


Moreover, wheat kernels infested by pupae–adults and insect-damaged kernels were identified with more than 99% accuracyby the same classifiers. Thus, no significant difference is observedbetween the classifiers in terms of the identification of the unin-fested and infested wheat kernels (Karunakaran et al., 2003). TheX-ray nondestructive method is used (Haff et al., 2006) to assesstranslucency in pineapple. The non-translucent samples were cor-rectly identified 95% of the time, whereas the translucent sampleswere correctly identified 86% of the time. Thus, X-ray imaging isproven to be a useful method for the selection of either free or ex-tremely translucent pineapples. Real-time X-ray inspection ofwheat was conducted to monitor infestation by the granary weevil.Sitophilus granarius was presented, with overall recognition resultsaveraging 84.4% accuracy for the images from the intensifier sys-tem vs. 90.2% for the film observations (Haff and Slaughter,2004). Uninfested kernels and kernels infested by four larvalinstars were properly recognized with up to 73% and 86%

Fig. 10. Sample images of peaches damage 4 (A, C, and E) and 6 (B, D, and F) days after esurface revealing no abnormalities; (E and F), internal injuries revealed after cutting op

classification accuracies by the statistical classifiers and BPNN,respectively, based on a study that identified wheat kernels dam-aged by the red flour beetle by using X-ray images (Karunakaranet al., 2004). This approach has great potential for use in defectdiscovery in pears (Lammertyn et al., 2003).

Internal freeze damage detection was performed in differentfruits using official procedures prescribed according to differentstandards by using numerous techniques. The automated detectionof fecal contamination of apples based on multispectral fluores-cence image fusion was conducted by Kim et al. (2005). The fluo-rescence emission bands at 670 nm provided the greatestpotential for the detection of feces contamination of apples. More-over, the investigation of multispectral fusion methods indicatedthat the band ratio image of 670–450 nm or 550 nm improves sen-sitivity of detection, whereas two-band ratios successfully detectcow feces contamination of apples regardless of apple colorationwith a 100% success rate by using unsupervised histogram-based

gg implantation. (A) and (B), X-ray images showing signs of injury; (C and D), outeren the peach (Yang et al., 2006).

Fig. 11. Location of electrodes in a pinna of Mimosa pudica (Volkov et al., 2010).


thresholding. Freeze damage detection in oranges by using ma-chine vision and ultraviolet fluorescence was conducted by Slaugh-ter et al. (2008). Based on a comparison with the existing USDAsegment cut method, the UV-fluorescence performed classificationshowed 70% accuracy, and the value increased to 86% for fruit withmoderate to severe levels of freeze damage. Tan et al. (2005) inves-tigated freeze damage detection in oranges by using gas sensorswith performance accuracy variation based on the sensor type;the best classification accuracy of carbon dioxide by using internalgas was 87% and 47% for unfrozen and partially frozen Valencia or-anges, respectively. The best classification accuracies were ac-quired by discrimination with ethanol using headspace gassampling, which correctly classified 100% of sound fruit and only37% of the partially frozen fruit. Moreover, the electronic nose sys-tem correctly classified approximately 73% and 74% of sound fruitand 70% and 67% of the partially frozen fruit with headspace andinternal gas sampling methods, respectively.

Given the capability of spectral reflectance NIR to detect thepresence of bruises on fruits, light distribution inside mandarinfruit during internal quality assessment by NIR spectroscopy illu-minated with an 808 nm laser light show a rapid reduction in lightlevel across the thick illuminated skin. A less rapid but still highreduction was observed as the light continued to diffuse into theflesh (Fraser et al., 2003). The detection of bruises on apples byusing NIR reflectance spectroscopy was investigated, yielding gooddiscrimination between apples before and after compression. Nev-ertheless, the capacity of NIR spectroscopy to detect bruised applesvaried according to the type and stage of development (Guillerminet al., 2005). Defect and ripeness of citrus were inspected by usingthe NIR transmission spectrum, and a ripeness inspection modelwas developed based on the wavelength difference as a ripenesscriterion with 91% accuracy of ripeness estimation compared withvisual inspection data (Kim et al., 2004). Both interactions in thelong-wave NIR and the transmission in the visible and short-waveNIR wavelength ranges display a clear advantage over the reflec-tance for every range in terms of properly distinguishing infestedjujubes from intact jujubes based on the nondestructive detectionof internal insect infestation in jujubes by using visible and NIRspectroscopy (Wang et al., 2011).

Furthermore, an NMR study on internal browning in pears wasconducted by Hernandez-Sanchez et al. (2007). The former and thelatter types of images enabled the correct classification of up to94% and 96% of pears, respectively, whereas the minimum affectedvalue of tissue was evidently recognized and internal bruising pre-diction in watermelon was studied and compressed using NMRand nonlinear models. The results indicate that (1) equivalentstresses in the red flesh are higher than the failure stress in bothvarieties for Crimson sweet (27 kPa) and Charleston gray(37 kPa), (2) the bruise of the red flesh is the primary form ofmechanical damage of watermelons under compression in bothdirections, and (3) the nonlinear FEA data can predict bruising inwatermelons under different load conditions. The experiment con-cludes that multiple optimal waveband images are capable ofbuilding a multispectral detection system for hidden bruises onkiwifruits, given that the error of hidden bruise recognition offruits was 12.5% (Lü et al., 2011; Sadrnia et al., 2008).

Numerous applications for capacitance and inductance probingsensors in agriculture quality estimation have been used bynumerous researchers worldwide. They evaluated factor dielectricconstant and loss of materials that showed a relationship well witha some quality factors of the products such as moisture contentand ripeness as well as damage (Soltani et al., 2011). Furthermore,Liu (2006) investigated that the comparatively new method basedon electrical impedance spectroscopy (EIS) for food quality inspec-tion. This researcher concluded that (1) impedance measurementis capable of reflecting speedy changes when food has any physical

damage, such as chilling and bruising due to the ability of measur-ing the impedance variations from the physiological changes offood, such as wooliness or mealiness; (2) the relationships be-tween impedance and soluble solid content acid percent used toidentify the four apple varieties, namely, low-acid variety (Fujiand Red Delicious), high-acid variety (Granny Smith), and mediumacid variety (Pink Lady); and (3) the impedance arc had a propen-sity to fall when the moisture content was reduced from the initial95–65%, which indicates that the length of the diameter of theimpedance arc plot decreased with the loss of moisture. Moreover,measurements have been used to estimate the Effects of elevatedconcentrations of tropospheric ozone and carbon dioxide by meansof electrical impedance spectroscopy (EIS) (Repo et al., 2004). TheEIS properties of the leaves changed significantly during the grow-ing season when new leaves were expanding. The clones differed intheir EIS properties. Moreover, impedance parameters can offervaluable information on structural changes in the cell during theannual cycle of the plant.

Furthermore, properties of molecular electronics in pinnae ofMimosa pudica (Fig. 11) were investigated, and corresponding elec-trical circuits within the pinnae were proposed to explain theexperimental data (Volkov et al., 2010), whereas Non-destructivefreeze damage detection in oranges using machine vision andultraviolet fluorescence was investigated by Slaughter et al.(2008) in order to show that the UV fluorescence as shown inFig. 12 guarantee the ability of separating freeze-damaged fruitsubjected to moderate or severe freeze conditions.

On the other hand, development of microwave vapor heat treat-ment (MW-VHT) was performed by Varith et al. (2007) in order todisinfest Oriental fruit fly eggs in mangoes. MW-VHT causes lessheat damage of the mangoes compared with conventional VHT.Moreover, MW-VHT decreases the process time by more than90% during the preheating period. Shahak et al. (2004) introduceda new approach in order to improve the utilization of solar radia-tion by fruit trees which showed a positive effect on flowering,fruit-set, fruit size, color and internal quality and non-specificreduction of water stress, superficial damage and sunburn. In sim-ilar research, a study to evaluate the use of electrolyte leakagemeasurement in order to assess the radiation sensitivity of cutfresh crop was conducted. Radiation resistance varied among thevegetables, but the variance was unrelated to the endogenous anti-oxidant capacity or to phenolic content (Fan and Sokorai, 2005).

However, magnetic resonance imaging (MRI) is practical for theonline inspection of fruits to address the applicability of MRI in or-der to distinguish between undamaged and damaged orange fruits

Fig. 12. Photographs of freeze-damaged oranges showing the visual scores used to define the level of damage observed for the freeze treatments applied in the study. (A)0 = no damage, (B) 1 = slight damage, (C) 2 = noticeable damage, (D) 3 = moderate damage, (E) 4 = severe damage, and (F) 5 = extreme damage (Slaughter et al., 2008).


as illustrated in Fig. 13. Thus, the optimization of this applicationenables the improvement of MRI under dynamic conditions to re-duce motion artifacts and to detect light freeze damages (Hernán-dez-Sánchez et al., 2004). Based on the internal defect for insectdamage widely found in agricultural crops, MRI and CT were ap-plied in order to classify the different types of internal fruit infec-tions (Torres, 2007). On the other hand, (Milczarek et al., 2009)assessed tomato pericarp mechanical damage by using multivari-ate analysis of MRIs to develop an in-line system to detect dam-aged tissue during tomato processing. The MIA of the MR imagesof tomato is effective for the prediction of the conductivity scoreof pericarp tissue in tomatoes as well as for the rapid detectionof infestation of apple fruits by the peach fruit moth (Carposinasasakii matsumura) larvae by using a 0.2-T MRI apparatus. Thisapparatus can differentiate uninfested fruits from infested onesand can serve as a plant protection system to promote the conser-vation of natural ecology in foreign trade (Haishi et al., 2011).

Ultrasonic techniques have also been used by numerousresearchers in order to inspect fruit damage with different applica-tions of agricultural grading systems. The development of non-destructive way to test the fruit using scanning laser vibrometry(SLV), indicate the presence of damage or defects in fruit. The vari-ations of the average vibration spectrum of a grid of points or ofpoint-by-point signal velocity enabled the go-no-go recognitionof ‘‘firm’’ and ‘‘over-ripe’’ fruits, with notable success in the caseof mangoes, as reported by Santulli and Jeronimidis (2006). Theuse of non-contact ultrasonic measurements for the detection ofdamage and quality measurements of food products such as appleshowed good correlation between the ultrasound measurementsand the confined-compression destructive tests for each mealinesslevel as well as the potential for the rapid inspection of varioustypes of food products, as presented by Bechar et al. (2005) andGan et al. (2006). The parameters and techniques used for internalgrading systems of agricultural product such as fruit as well as

Fig. 13. MRI examples of both unaffected and affected oranges at different belt speeds and acquisition times (Hernández-Sánchez et al., 2004).


grain, vegetable and grass are summarized in Tables 2 and 3respectively.

4. Discussion and conclusion

This paper is a survey of recent methods and techniques thatmay be employed in signal processing for the non-destructiveinternal grading of agricultural products and their main tenets.

The grading systems in general utilize improved engineering tech-niques of image and signal processing of product’s internal charac-teristics such as sugar content, acid level or internal moisturecontent. The advantages as well as shortcomings of each of the dif-ferent techniques have been thoroughly elaborated.

Internal grading systems are comprised of specific sensors suchas hardware, connected to a high-speed computer with a dataacquisition system to intermediate between the sensor and com-puter with digital signal processing (DSP) capability to measure

Table 2Summary of parameters and techniques used with fruit internal grading systems.

Product Parameter Sensor Application References

Apple Pear content SPE-cartridge module Analyst Pear content determination Kolbener et al. (2006)Gas Electronic nose Evaluation of apple maturity Pathange et al. (2006)Sugar content Near-infrared spectrophotometer Quality assessment Xiaobo and Jiewen (2005)Firmness Impact tester Fruits sorting Jaren and Garcia-Pardo

(2002)Mealiness Ultrasonic measurements Determination of mealiness Bechar et al. (2005)Sugar content NIR spectra Prediction of sugar content Nicolaï et al. (2007)Bruises NIR Spectroscopy Detection of bruises on apples Guillermin et al. (2005)

Sweet cheery Gibberellic acid Resistant measurement Fruit cracking and quality Cline and Trought (2007)Sugar content Infrared Spectroscopy Fast determination of the ripeness stage Kwak et al. (2007)Internal insect infestation Transmittance spectroscopy Detecting and identify internal insect infestation Xing and Guyer (2008)

Strawberry Water content MRI Models for predicting water loss Evans et al. (2002)Banana Heating and damage Sequential infrared Study of banana dehydration using Pan et al. (2008)

Ripeness Capacitance sensing system Prediction of banana quality Soltani et al. (2010)Olive Fatty and acid content Fertilization and irrigation

treatmentsDetermination of fruit and oil characteristics Toplu et al. (2009)

Orange Freeze damage Gas sensors Freeze damage detection Tan et al. (2005)Light distribution NIR spectroscopy Internal quality assessment Fraser et al. (2003)Freeze damage Ultraviolet fluorescence Non-destructive freeze damage detection Slaughter et al. (2008)Seeds and freeze damage Magnetic resonance imaging Fast detection of seeds and freeze damage Kim et al. (2008)

Pomelo Fresh-cut NIR transmittance Evaluation of internal quality Puangsombut et al. (2012)Lemon Acid and sweet HPLC with a RI detector Selection of the optimal rate Váchová et al. (2009)Mango Leaves Electronic nose Fruits ripeness determination Salim et al. (2005)Pineapple Pineapple mash Ultrasound Fruit treatment for juice processing (Tran and Le (2011)Kiwifruit Dry matter NIRS Long-term prediction of kiwifruit dry matter Lu et al. (2010)

Soluble solids content FT-NIRS Soluble solids content determination Chen and Han (2012)Dry matter and solublesolids

Near infrared Density comparing of NIR methods McGlone et al. (2002)

Peaches Aroma Electronic nose Fruit characteristics measurement Natale et al. (2002)Evolution monitoring Acoustic and impact methods Fruit firmness evolution monitoring during

storageDiezma-Iglesias et al.(2006)

Ripeness Electronic nose Non-destructive tool of peach cultivarscharacterizing

Benedetti et al. (2008)

Apricots Sugar content FT-NIRS Evaluation of fruit authenticity and content Kurz et al. (2009)Pears Acid content and SSC Magnetic resonance Quality and internal characteristics Zhou et al. (2008)Pear seed oils Fatty acid GC–MS analyzer Composition and rheological behavior Ennouri et al. (2005)Red globe

grapePhysical and chemicalquality

X-ray irradiation X-ray irradiation effect study on the fruit Kang et al. (2012)

Oil palm Moisture Microwave Fruit ripeness determination Yeow et al. (2010)Flavonoids andanthocyanin

Fluorescence sensor Fruit ripeness determination Hazir et al. (2012a,b)

Maturity Portable four-band sensor system Oil palm fruit classification Saeed et al. (2012)Fruit peel Pectin acid Composite design Pectin acid extraction Kliemann et al. (2009)Fruit Juice Ascorbic acid Cyclic voltammeter Ascorbic acid content determination Pisoschi et al. (2008)

Ascorbic acid Differential pulse voltammeter Ascorbic acid content determination Pisoschi et al. (2011)

SPE = solid phase extraction, NIR = near infrared, HPLC = high-performance liquid chromatographic, RI = refractive index, FT-NIRS = Fourier transform near-infrared spec-troscopy, SSC = soluble solids contents, GC–MS = Gas chromatography and mass spectrometry.


the products internal properties such as moisture, sugar, acid con-tents or internal fruit damage. Processing can be in the form of dig-ital audio signal processing, digital control engineering, speechprocessing, RADAR signal processing, communications or signalprocessing. The general steps involved in digital signal processingof internal grading include data acquisition as sensor electronics,pre-processing as A/D converter, signal processing as a single boardembedded DSP, features extraction and classification. In summary,internal grading systems are used to measure different types of sig-nals of fruit internal characteristics such as (moisture, sugar, acid,ripeness and internal fruit damage) using various sensor combina-tions specific to internal properties.

Moisture measurements are efficient indicators of the internalfeatures and characteristics of fruit and can thus be used in differ-ent applications to obtain valuable information on fruit. A consid-erable amount of research has been conducted on the generalrelationships between plant responses and soil moisture condi-tions by using different techniques such as microwave sensor forsoil moisture determination, microwave moisture meter for mois-ture measurement in dried fruits, as well as the physical propertiesof various crops, as presented early in this paper. In addition, MRI

was used for the real-time measurement of the moisture profilechange in plants, particularly for boiling rice grain. Capacitanceprobes were used to monitor soil water continuously and accu-rately. Other researchers used EIS to measure the impedance spec-tra of agricultural crop slices during drying to correlate impedanceparameters with moisture content during different drying periods.Their results are useful in the drying, storage, marketing, and pro-cessing of fruit based on the dielectric behavior of the food mate-rials, which are significantly affected by their water content. Theresearch results prove that the combination of electric fields andvacuum impregnation could significantly enhance the freezing tol-erance of fruit including spinach leaves. Additionally, microwavemoisture sensing can provide an accurate measurement of mois-ture content of fruit such as durian. This method is capable of pre-dicting the day-after postharvest. In addition, this methoddemonstrates that the use of higher microwave frequencies is bet-ter than the use of lower frequencies. Radiation measurement isone of the most popular methods used to estimate agriculturalcrop quality based on moisture. Furthermore, the use of a high-res-olution ultrasonic thermometer is an important method used tomeasure absorbed dose in water calorimeters. The fruit dry matter

Table 3Summary of parameters and techniques used with grains, vegetable and grass internal grading systems.

Product Parameter Sensor Application References

Wheat Amino acid content Stable mass spectrometry Amino acid content of food materials Wolf and Zainal (2002)Breeding, trade andprocessing

Near infrared spectroscopy Advanced analytical tool in wheatparameters

Pojic and Mastilovic(2012)

Root, shoot length, andweight

Gamma radiation The effects of gamma radiationdetermination

Borzouei et al. (2010)

Soybean Moisture Measuring empting angle of repose Evaluating the moisture content effect Tavakoli et al. (2009)Jellybean Moisture MRI Water activity measurements Troutman et al. (2001)Rice Moisture content Designing the equipment for processing Physical properties study Varnamkhastia et al.

(2008)Moisture distribution MRI Water distribution and migration

examinationHwang et al. (2009)

Faba bean Moisture content Static and kinetic coefficients of frictiondetermination

Physical properties evaluation Altuntas and Yıldız(2007)

Fenugreek Moisture content Static and kinetic coefficients of frictiondetermination

Physical properties evaluation Altuntas et al. (2005)

Lentil seeds Moisture content Static and kinetic coefficients of frictiondetermination

Physical properties evaluation Amin et al. (2004)

Seed Moisture Physical and mechanical propertiesmeasurements

Seed moisture study Bamgboye and Adebayo(2012)

Beans Moisture Infrared and microwave Food moisture determination El-Sayd and Makawy(2010)

Popcorn Damage Property covariance features Detection of fungal damaged popcorn Yorulmaz et al. (2012)Potatoes Interior MRI Segment and assess the interior of

potatoesMartens et al. (2002)

Relaxation parameters Low-field NMR relaxation and NMR-imaging

Determination of dry matter content inpotatoes

Thyboa et al. (2003)

Broccoli and sweetpotato

Acidfied Continuous microwave process Packaged acidified vegetablespasteurization

Koskiniemi (2010)

Tomato Yield and chemicalcomposition

Preharvest treatment Effects of preharvest treatments study Meaza et al. (2007)

Damage MRI Assessment of tomato mechanicaldamage

Milczarek et al. (2009)

Mechanical damage Experiment and shelf life observation Effect study of mechanical damagedegree

Li et al. (2010)

Peeling outcome MRI Prediction of processing tomato peelingoutcomes

Milczarek and Mccarthy(2011)

Ripening ethylene Solar UV-B UV-B radiation influences study Becatti et al. (2009)Tea Varieties FT-NIR spectroscopy Tea identification Chen et al. (2008)Leaf Amino acid GC-TOF-MS Leaf extracts Noctor et al. (2007)

Leaf water content NIR spectroscopy analysis Rapid determination of leaf watercontent selection

Zhang et al. (2012)

Odor and taste Electronic nose and tongue Instrumental testing of tea Banerjee(Roy) et al.(2012)

MRI = magnetic resonance images, NMR = nuclear magnetic resonance, FT-NIR = Fourier transform near-infrared, GC-TOF-MS = Gas chromatography coupled to time-of-flightmass spectrometry, UV-B = ultraviolet-B.


of unripe fruit such as kiwifruit can be predicted by NIR spectros-copy, whereas the MRI technique is useful for the non-intrusivemonitoring of in vivo water content changes in the different partsof the leaves during drought stress by using a five-port reflexome-ter. This simple, cheap, and efficient microwave network analyzersolution can determine reflection coefficients that can be used todetermine directly the moisture content in fruits as well as theMR parameters of water in fresh and frozen-thawed cod by usingMRI. All the storage periods studied showed significant changes.

Sugar measurements still require major analysis in most areasof agricultural crop application, as per the aforementioned, sugarcontent can be used as a matrix to evaluate fruit quality and matu-rity. Literature reviews show that NIR is a reliable technique forfruit sugar measurements based on the critical wavelet level deter-mination of sugar content. On the other hand, other techniquessuch as microwaves facilitate the non-destructive imaging of fruitsugar distribution, which confirmed that the sugar distribution in-side the fruit varies according to the harvest time, with an ultra-sonic condition being the optimum for the sucrose productiontechnique. A correlation study of the sugar and frequency domainparameters of the fruit by using EI techniques as well as radiationvariation among the different types of vegetables and fruit that areused for sugar measurement application, is recommended, given

that different result accuracies are obtained based on the fruittypes. In addition, MRI is a useful tool for identifying the changesin postharvest structure based on sugar measurements for fruitssuch as kiwifruit. The hyperspectral imaging technique is poten-tially useful for assessing the sugar content of apple based on thecorrelation coefficient (r) between the hyperspectral imaging pre-diction results and the reference measurement.

However, aside from other fruit components such as fruit acidmeasurement is another integral factor for fruit usage that is re-quired to determine the acid ratio to be used in different applica-tions based on various human health situations. NIRspectroscopy analysis was used by selecting a set of wavelengthsthat are most effective in measuring the pH level of fruit solutions.Furthermore, X-ray and CT are reliable techniques for internal acidcontent evaluation of fruit, which proves that the titratable aciditysignificantly decreased with postharvest ripening time, whereaspH level and soluble solids increased with postharvest ripeningtime. Moreover, capacitance and ultrasound are also utilized forfruit acid measurement. The change in energy of ultrasonic waveswas used as an indicator of higher oil wreckage range. On the otherhand, the change in the maximum reflection at the resonant fre-quency of the capacitance method circuit was employed to indi-cate oil debris with a lower range of size. The possible


connections between EI and the main parameters of fruit tastemade EI one of the most important methods used for fruit acid esti-mation and measurements, especially for fruit seasonal variationestimation. The electrical properties of plant tissue as well as fruittaste assortment were categorized as low-acid, high-acid, andmedium-acid assortment. In addition, the application of continu-ous microwave processing to acidified vegetable products could re-duce energy usage and water consumption, thereby improving thesustainability of acidified vegetable production. Numerous studieson acid concluded that the MRI is the most suitable technique forthe study of the improvement of core breakdown disorder duringpostharvest storage.

Given that the market quality of agricultural crop and industrialfood products is estimated based on the fruit ripeness measure-ments, proper experiments with suitable techniques for fruit inter-nal ripeness grading system are determined in this paper. Theelectronic nose system is developed and proven eligible for deter-mining fruit ripeness at each stage of fruit maturity. Additionally,NIR spectroscopy is also employed for the non-invasive assessmentof fruit maturity. MRI analysis by using sensory perception and hu-man perception as well as evaluations on an interior piece of fruitsuch as potato is proven fairly accurate and could thus be imple-mented in an online fruit sorting system. Moreover, such an ap-proach is a non-invasive way of controlling fruit maturityassessment based on the capacitance sensing system, which iscapable of classifying the fruits during ripening period and ofassessing changes based on the quality parameters.

Furthermore, electrical impedance is a popular method used forfruit-ripeness quality estimation based on the observed change inthe electrical impedance; it is also recommended for the analysisof fruit pulp and of the effects of drying and freezing–thawingtreatments on fruit impedance characteristics. The membranes ofthe cells with dielectric properties in the tissue were significantlydamaged during the freezing process, which, along with micro-wave, was considered the main reason for post-thawing deteriora-tion in the quality attributes of frozen products. These factors areconsidered as the imaging principles for agricultural crop. Theapplication of ultrasound to inspect fruit ripeness quality is basedon fruit firmness, with a good relationship observed between thebeam and reduced ultrasound. Numerous studies compared theperformances of the MRI and X-ray. The MRI has the advantageof a shorter processing time than the X-ray based on the develop-ment study of core breakdown, whereas X-ray can perform non-destructive detection because it is more convenient and less costlycompared with the MRI.

Agricultural research centers around the world concentrate onthe development of internal grading systems for agricultural cropsto address this phenomenon. Several methods and techniques areused for fruit internal damage detection, but some of them aremore strongly recommended. For example, the accuracy percent-age results for the spectral analysis of permeability show that ithas a strong potential for the detection of pests in the fruit, X-rayhas great potential for use in defect discovery in apples, and mul-tispectral and ultraviolet fluorescence can address severe levels offruit freeze damage by using gas sensors and the electronic nosesystem. In addition, spectral reflectance NIR was proven capableof detecting the presence of bruises on the fruits and can thus beused according to the type and stage of development. EIS andcapacitance and inductance probing sensors have numerous appli-cations in agricultural fruit damage estimation and have thus beenused by numerous researchers worldwide. MW-VHT was devel-oped and was proven to cause less heat damage to the fruit, thusdecreasing the process time by more than 90% during the preheat-ing period. However, MRI is practical for the online inspection offruits, is capable of distinguishing between undamaged and dam-aged fruits. Moreover, MRI can perform well under dynamic condi-

tions in terms of reducing motion artifacts and detecting lightfreeze damages.

In addition, quality inspection of agriculture via internal grad-ing systems has some challenges, for instance limitations on theaccuracy and speed, which have effects on the quality featuresdue to some controlled and uncontrolled factors, for example:

� Inappropriate system design may produce signals with unclearinformation due to the use of inappropriate software and hard-ware equipment. This may possibly occur due to an improperstudy of the specific application.� The accuracy of system results have covariant relations with the

accuracy of the training data estimated by human vision andused as base data for further sample classification.

Acknowledgments

This research work was supported by Universiti Putra Malaysia(UPM), Spatial and numerical modeling lab (SNML), spatial re-search group (SRG), Malaysian Palm Oil Board (MPOB), Ministryof Science, Technology and Innovation (MOSTI) Malaysia, and also Iwould like to acknowledge the two anonyms reviewers who pro-vided contractive comments of the early draft of this paper submit-ted to the journal. Their comments help us to improve this papertremendously.

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http://dx.doi.org/10.1111/j.1745-4603.2012.00354.x


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the application of internal grading system technologies for agricultural products â€“ review

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