Research note

Some physico-mechanic properties of terebinth(Pistacia terebinthus L.) fruits

Cevat Aydın a,*, Musa €OOzcan b

a Department of Agricultural Machinery, Faculty of Agriculture, University of Selc�uk, 42031 Konya, Turkeyb Department of Food Engineering, Faculty of Agriculture, University of Selc�uk, 42031 Konya, Turkey

Received 20 April 2001; accepted 27 July 2001

Abstract

Several physical properties of terebinth fruits were evaluated as functions of moisture content. The average length, width,

thickness, the geometric mean diameter and unit mass of the fruits were 6.10 mm, 5.30 mm, 4.96 mm, 5.43 mm, 0.0565 g, respectively

at 6% moisture content dry basis. Studies on rewetted fruit showed that as moisture content increased from 6% to 26% dry basis

(d.b.) kernel and bulk density increased from 1031 to 1071 kg=m3and from 449 to 620 kg=m

3, respectively. While increasing

moisture content, porosity decreased from 56% to 42%, projected areas increased from 0.23 to 0:26 cm2 and terminal velocity

increased from 6.3 to 8.18 m/s. The rupture strength decreased with increasing moisture. � 2002 Elsevier Science Ltd. All rights

reserved.

1. Introduction

The terebinth tree, Pistacia terebinthus L. (Anacar-diaceae), ranging in size from a shrub to a small tree(about 2–6 m), is widely distributed in the Middle Eastand Southern Europe. The fruits are panuculate, glo-bose or broadly obovate of approximate size 5–6� 4–6mm. Two sub species may be recognised, though inter-mediates are rather common in Turkey (Davis, 1967).The fruits have been used as appetisers in the diet inSouth Turkey for several thousand years. The fruits arealso used in baking of a speciality village bread. Theplant is rich in tannin and resinous substances and hasbeen known for its aromatic properties (Baytop, 1984).Harvesting and handling of the crop are carried out

manually in Turkey. The threshing is usually carried outon a hard floor with a home-made threshing machine.To optimize threshing performance, pneumatic con-veying, storing and other processes of terbinthus fruit,its physical properties must be known.The aim of this study is to determine the physico-

mechanic properties of terenbinth fruits growing wild inTurkey.The aim of this work was to investigate the depen-

dence of physical properties such as linear dimensions,unit mass, sphericity, densities, porosity, projected area,

terminal velocity and rupture strength of fruits on somecontent.

2. Materials and methods

2.1. Material

Fruits were collected from plants growing wild in _IIc�el(B€uuy€uukeceli–G€uulnar ) in Turkey during September 2000.Plants were identified by the botany department, Selc�ukUniversity, Konya, Turkey. The fruits were cleaned inan air screen cleaner to remove all foreign matter such asdust, dirt, stones and chaff as well immature and brokenseeds. The initial moisture content of the seeds was de-termined by using a standard method (USDA, 1970)and was found to vary between 6 and 6.4% d.b.

2.2. Methods

Fruit samples of the desired moisture levels wereprepared by adding calculated amounts of distilledwater, then mixing and sealing in separate polyethylenebags. The samples were kept at 278 K in a refrigeratorfor 7 day to allow the moisture to distribute uniformlythroughout the sample. Before starting a test, the re-quired quantities of the fruit were allowed to warm up to

Journal of Food Engineering 53 (2002) 97–101

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room temperature (Dehspande, Bal, & Ojha, 1993;Demir & €OOzcan, 2001; C�arman, 1996).All the physical properties of the fruit were assessed

at moisture levels of 6, 13 and 26% d.b. with five repli-cations at each level.To determine the average size of the fruit a sample of

one hundred fruits was randomly selected. Measurementof the three major perpendicular dimensions at the fruitwere carried out with a micrometer to an accuracy of0.01 mm.The geometric mean diameter ðDpÞ of the fruit was

calculated by using the following formula (Mohsenin,1970):

Dp ¼ ðLWT Þ1=3;

where L is the length, W is the width and T is thethickness.According to Mohsenin (1970), the degree of sphe-

ricity ðUÞ can be expressed as follows:

U ¼ ðLWT Þ1=3

L100:

This equation was used to calculate the sphericity ofterebinth fruit in the present investigation.To obtain the mass, each fruit was weighed on a

balance reading to 0.001 g.The kernel density of a fruit is defined as the ratio of

the mass of a sample of a fruit to the solid volume oc-cupied by the sample (Dehspande et al., 1993). The fruitvolume and its kernel density were determined using theliquid displacement method. Toluene ðC7H8Þ was usedin place of water because it is absorbed by fruits to alesser extent. Also, its surface tension is low, so that itfills even shallow dips in a seed and its dissolution poweris low (€OOg€uut, 1998; Sitkei, 1986). The bulk density isthe ratio of the mass of a sample of a fruit to its totalvolume. It is a moisture dependent property. The bulkdensity was determined with a weight per hectolitretester which was calibrated in kg per hectolitre (Dehs-pande et al., 1993). The fruits were poured into thecalibrated bucket up to the top from a height of about15 cm and excess fruits were removed by a woodenblade. The fruits were not compacted in any way.

The porosity ðeÞ of bulk seed was computed from thevalues of kernel density and bulk density using the re-lationship given by Mohsenin (1970) as follows:

e ¼ qk � qbqk

100;

where qb is the bulk density and qk is the kernel density.The projected area of a seed was measured by placing

it under thin transparent paper and using a planimeterequipped with a magnifying glass (Makanjuola, 1972).The terminal velocities of fruits and fractions at dif-

ferent moisture contents were measured using an aircolumn. For each test, a small sample was dropped intothe air stream from the top of the air column, up whichair was blown to suspend the material in the air stream.The air velocity near the location of the fruit suspensionwas measured by an electronic anemometer having anaccuracy of 0.1 m/s (Joshi, Das, & Mukherjee, 1993).Five replications were made for each fruit sample(Fig. 1).To determine the rupture strength of seeds, a bio-

logical material test device was used. The device devel-oped by Aydın and €OOg€uut (1992), has three maincomponents which are a stable forced and movingplatform, a driving unit (AC electric motor and elec-tronic variator) and a data acquisition (Dynamometer,amplifier and XY recorder) system. The fruit was placedon the moving lower platform at the 0.0004 m/s speedand pressed with fixed upper platform. The ruptureforce of fruit was measured by the data acquisitionsystem (Fig. 2).

Nomenclature

Dp geometric mean diameter (mm)L length (mm)Vt terminal velocity (m/s)W width (mm)T thickness (mm)U sphericity (%)e porosity (%)

Pa projected area ðcm2Þqb bulk density ðkg=m3Þqk true density ðkg=m3ÞMc moisture content (%) d.b.Pr rupture force (N)R2 determination coefficient

Fig. 1. Unit for measuring terminal velocity.

98 C. Aydın, M. €OOzcan / Journal of Food Engineering 53 (2002) 97–101

3. Results and discussion

3.1. Dimensions and size distribution of fruits

Table 1 shows the size distribution of the terebinthfruits. The dimensions show a trend towards a normaldistribution. About 80% of the fruits have a lengthranging from 6.01 to 6.19 mm, about 80% have a widthranging from 5.22 to 5.38 mm, and about 80% have athickness ranging from 4.84 to 5.08 mm. The values ofmass and, sphericity are given in Table 1. The averagevalues of the geometric mean diameter and sphericitywere calculated as 5.43 mm and 89%, respectively. Kuraland C�arman (1997) has reported the values for thesphericity of chick pea as 83.2% which is close to theresults of this investigation.

3.2. Bulk density

The bulk density of fruits at different moisture levelsvaried from 449 to 620 kg=m3

(Fig. 3) an increased inbulk density with an increase in moisture content wasapparent. The bulk density of fruit was found to havethe following relationship with moisture content:

qb ¼ 409:27þ 8:3155Mc ðR2 ¼ 0:9742Þ:

4. Kernel density

The true density at terebinth at different moisturelevels varied from 1031 to 1071 kg=m

3. The effect of

moisture content on kernel density showed an increasewith moisture content (Fig. 3). This phenomenon maybe attributed to the possible small volume expansion ofindividual fruit on moisture gain. The variations inkernel density with moisture content can be representedby following correlation:

qk ¼ 1020:9þ 1:961Mc ðR2 ¼ 0:9871Þ:

4.1. Porosity

Since the porosity depends on the bulk density aswell as on the true or kernel densities, the magnitude ofthe variation in porosity depends on these factors only.Porosity was found to slightly decrease with increase inmoisture content from 6% to 26% d.b. as shown in Fig. 4the relationship between the porosity and moisturecontent is as shown below:

e ¼ 59:29� 0:6816Mc ðR2 ¼ 0:9762Þ:The form of the plot is similar to that for pigeon pea asfound by Shepherd and Bhardwaj (1986).

4.2. Projected area

The projected area of terebinth fruits (Fig. 5) in-creased by about 11.1%, while the moisture content ofterebinth increased from 6% to 26% d.b. Similar trends

Fig. 2. Biological material test unit (BMTU).

Table 1

Means and standard errors of the terebinth dimensions at 6% d.b.

Length, mm 6.10� 0.07Thickness, mm 4.96� 0.09Width, mm 5.30� 0.06Geometric mean diameter, mm 5.43� 0.08Sphericity, % 89.1� 0.35Mass, g 0.056� 0.00095

Fig. 3. Effect of moisture content on density: (�) kernel; ð�Þ bulk.

Fig. 4. Effect of moisture content on porosity.

C. Aydın, M. €OOzcan / Journal of Food Engineering 53 (2002) 97–101 99

were reported for many other seeds (Mohsenin, 1970;Sitkei, 1986). Dehspande et al. (1993) found that thesurface area of soybean grain increased from 0.813 to0:952 cm2, when the moisture content was increasedfrom 6% to 26% d.b. The projected area of fruit wasfound to have the following relationship with moisturecontent:

Pa ¼ 0:2232þ 0:0015Mc ðR2 ¼ 0:9709Þ:

4.3. Terminal velocity

The experimental results for the terminal velocity ofthe fruits at various moisture levels are plotted in Fig. 6.As moisture content increased, the terminal velocity wasfound to increase linearly. The results are similar tothose reported by Kural and C�arman (1997), but thevalues were higher than those for pumpkin seeds andcereals (Gorial & Callaghan, 1990; Joshi et al., 1993).The increase in terminal velocity with increase in mois-ture content can be attributed to the increase in mass ofan individual fruit per unit frontal area presented to theair stream. As moisture content increased, the terminalvelocity was found to increase linearly

Vt ¼ 5:659þ 0:099Mc ðR2 ¼ 0:972Þ:

4.4. Rupture strength

The results of the rupture strength tests are presentedin Fig. 7. The results show that the rupture strength is

highly dependent on moisture content for the rangemoisture content investigated (6% to 26% d.b.). Greaterforces were necessary to rupture the fruits at lowermoisture contents. The small rupturing forces at highermoisture content might have resulted from the fact thatthe fruit tended to be very brittle at high moisturecontent. The relationship between the rupture strengthsand moisture content of the terebinth can be representedby following correlation:

Pr ¼ 75:56� 1:032Mc ðR2 ¼ 0:93Þ:

The results are similar to those reported by Liang, Chin,and Mitchell (1984) and Dursun (1997).

References

Aydın, C., & €OOg€uut, H. (1992). Determination of deformation energy insome biological materials. In National Symposium on Mechanisa-

tion in Agriculture (pp. 254–264). Turkey: Samsun.

Baytop, T. (1984). Phytotherapy in Turkey _IIstanbul Univ. Publ. No.

2355, Istanbul, Turkey (in Turkish).

C�arman, K. (1996). Some physical properties of lentil seeds. Journal ofAgricultural Engineering Research, 63, 87–92.

Davis, P. H. (1967). Flora of Turkey and the East Aegean Islands

(Vol. 2) (pp. 546–547). Edinburgh: University Press.

Dehspande, S. D., Bal, S., & Ojha, T. P. (1993). Physical properties of

soybean. Journal of Agricultural Engineering Research, 56, 89–98.

Demir, F., & €OOzcan, M. (2001). Chemical and technological propertiesof rose (Rosa canina L.) fruits grown wild in turkey. Journal of

Food Engineering, 47, 333–336.

Dursun, I. G. (1997). Determination of the shelling resistance of some

products under the point load. In National Symposium on Mech-

anisation in Agriculture (pp. 950–957). Turkey: Tokat.

Gorial, B. Y., & Callaghan, J. R. (1990). Aerodynamic properties of

grain/straw materials. Journal of Agricultural Engineering Research,

46, 275–290.

Joshi, D. C., Das, S. K., & Mukherjee, R. K. (1993). Physical

properties of pumpkin seeds. Journal of Agricultural Engineering

Research, 54, 219–229.

Kural, H., & C�arman, K. (1997). Aerodynamic properties of seedcrops. In National Symposium on Mechanisation in Agriculture

(pp. 615–623). Turkey: Tokat.

Liang, T., Chin, L., & Mitchell, J. B. (1984). Modeling moisture

influence on macadamia nut kernel recovery. Transaction-ASAE,

27, 1538–1541.

Makanjuola, G. A. (1972). A study of some of the physical properties

of melon seeds. Journal of Agricultural Engineering Research, 17,

128–137.Fig. 6. Effect of moisture content on terminal velocity.

Fig. 7. Effect of moisture content on rupture force at terenbithus.Fig. 5. Effect of moisture content on projected area.

100 C. Aydın, M. €OOzcan / Journal of Food Engineering 53 (2002) 97–101

Mohsenin, N. N. (1970). Physical properties of plant and animal

materials. New York: Gordon and Breach Science Publishers.€OOg€uut, H. (1998). Some physical properties of white lupin. Journal of

Agricultural Engineering Research, 56, 273–277.

Sitkei, G. (1986). Mechanics of agricultural materials. Budapest:

Akademiai Kiado.

Shepherd, H., & Bhardwaj, R. K. (1986). Moisture-dependent physical

properties of pigeon pea. Journal of Agricultural Engineering

Research, 35, 227–234.

USDA (1970). Official grain standards of the United States. US

Department of Agricultural Consumer and Marketing Service

Grain Division, Revised.

C. Aydın, M. €OOzcan / Journal of Food Engineering 53 (2002) 97–101 101