osmotic dehydration of pomegranate seeds: mass transfer kinetics and differential scanning...

Original article

Osmotic dehydration of pomegranate seeds: mass transfer kinetics

and differential scanning calorimetry characterization

Brahim Bchir,1 Souhail Besbes,2 Hamadi Attia2 & Christophe Blecker1*

1 Department of Food Technology, Gembloux Agricultural University, Passage des Deportes, 2, B-5030 Gembloux, Belgium

2 Laboratory of Food Analyses, National Engineering School of Sfax, Route de Soukra, 3038 Sfax, Tunisia

(Received 9 April 2009; Accepted in revised form 3 August 2009)

Summary Osmotic dehydration of pomegranate seeds was carried out at different temperatures (30, 40, 50 �C) in a

55�Brix solution of sucrose, glucose, and mixture sucrose & glucose (50:50, w ⁄w). The most significant

changes of water loss and solids gain took place during the first 20 min of dewatering. During this period,

seeds water loss was estimated to 46% in sucrose, 37% in glucose and 41% in mix glucose ⁄ sucrose solution.The increase of temperature favoured the increase of water loss, weight reduction, solids gain and effective

diffusivity. Differential scanning calorimetry data provided complementary information on the mobility

changes of water and solute in osmodehydrated pomegranate seeds. The ratio between % frozen water and

% unfreezable water decreased from 5 to 0.5 during the process. That involving the presence of very tightly

bound water to the sample, which is very difficult to eliminate with this process. It also appeared that glass

transition temperature depends on the types of sugar.

Keywords Differential scanning calorimetry, osmotic dehydration, pomegranate, solids gain, water loss.

Introduction

Pomegranate (Punica granatum L.) is one of the mostimportant fruits in Tunisia. Its total production in 2008reached more than 70 000 tons. Pomegranate is com-posed by a non edible part formed by 30% of skin(external part) and 13% of internal lamel and an ediblepart formed by seeds (50–70%). Pomegranate seeds arecomposed by 15% pips (woody part), this part deter-mines the hardness, and 85% pulp (the juicy part)depending on cultivar (Al-Maiman & Ahmad, 2002).The edible part of the fruit contains considerable

amounts of sugars, vitamins, organic acids, phenoliccompounds and minerals (Espiard, 2002). In Tunisia theresearch of addition value to pomegranate seeds is verylimited and presents a traditional feature such as jampreparation or direct consummation of fruit during thecrop season (between September and December). How-ever, other perspectives of transformation and exploita-tion of the pomegranate seeds should be undertaken togive value addition to this typical fruit. As reported inthe literature, seeds could be used for preparation ofgrenadine (Adsule & Patil, 1995), fresh juice (Espiard,2002), jelly (Maestre et al., 2000), jam (Espiard, 2002),

wine (Altan & Maskan, 2004), spice (Adsule & Patil,1995), paste, flavoring and coloring drinks and mainly insome new cosmetics application (Espiard, 2002). More-over, recently, more than 475 new products containingpomegranate (food and drinks) were born on theAmerican market. These included, chewings-gum calledpomegranate Power, sausage of chicken to the pome-granate, ices, breads, and biscuit with pomegranate(Storey, 2007).The demand for healthy, natural and tasty processed

fruits increased continuously, not only for finishedproducts, but also for ingredients that can be includedin some food formulation such as ice-cream, cereals,dairy, confectionery and bakery products. In fact, overthe last few decades, a lot of research studies aboutprocessing of fruits and vegetables (Vivanco et al.,2004), meat and fish (Ivan et al., 2007) were developedusing osmotic dehydration (OD). This process consistsin the immersion of the product in a concentratedsolution (sugar, salt, sorbitol, glycerol), generating apartially dehydrated and impregnated product (Torr-eggiani & Bertolo, 2001). Osmotic dehydration has a lotof benefit, like the use of a low energy and costcompared to other dehydration methods. In addition, itinvolves effective inhibition of polyphenoxidase, pre-vention of loss of volatile compounds, even undervacuum and reduction of heat damage to colour and

*Correspondent: Fax: +32(0)81 ⁄ 60.17.67;e-mail: [email protected]

International Journal of Food Science and Technology 2009, 44, 2208–22172208

doi:10.1111/j.1365-2621.2009.02061.x

� 2009 The Authors. Journal compilation � 2009 Institute of Food Science and Technology

flavour during dehydration (Krokida et al., 2001).Raoult-Wack et al. (1991) noticed that OD did notstrongly deteriorate the texture of fruits. This effect wasexplained by the protective function of sugars in thefruit tissue.Nowadays, the industry uses this technique for some

previously cutted fruit like apple, banana, mango,apricot, between others. This process has not been usedfor the conservation of whole pomegranate seeds,neither by scientifics nor by industrials.The aim of this work was firstly to investigate the

kinetics of osmotic dehydration and to determine theinfluence of osmotic conditions, such as temperatureand osmotic solutions on mass transfer during osmoticdehydration of whole pomegranate seeds. And secondlyto characterise the internal changes in osmoticallydehydrated pomegranate seeds in sucrose, glucose andmixture sucrose & glucose using differential scanningcalorimetry (DSC). Also to quantify the different statesof water in the seeds, and to study the influence ofosmotic dehydration process on different parameterslike the glass transition temperature.

Materials and methods

Preparation of pomegranate seeds

Fresh pomegranate fruits (Punica granatum L.) of ElGabsi variety were obtained from a local research centrein Gabes, Tunisia. Pomegranates fruits were collected atfull ripeness stage, having the same size. The fruits(20 kg) were washed in cold tap water and then frozen at)50 �C. Pomegranates were thawed, during 1 h at roomtemperature, and seeds were recuperated in bottles justat the moment of osmodehydrated process. During thethawing of the seeds, 24 mL of juice per 100 g of freshmatter were percolated.

Osmodehydration process

Sucrose, glucose and their mixture (50:50, w ⁄w) weredissolved in water in order to obtain 55�Brix solu-tions. About 10 g of seeds was soaked in the sugarsolution and were placed in bottles (Schott, Saint-Gallen, Switzerland) of 100 mL. The volume ratiobetween the seeds and the sugar solution was kept atone part of seeds and four parts of solution (1:4).Osmotic dehydration process was conducted during20–120 min in a shaking water bath (GFL instrumentD 3006, Germany; oscillation rate 160 rpm) at differ-ent temperatures (30, 40, and 50 �C).

Mass transfer kinetics

Seeds were removed from the immersion solution atselected time intervals (0, 20, 40, 60, 80, 100 and

120 min) and were quickly rinsed (with distilled water)and the excess of solution at the surface was removedwith absorbent paper. Water activity and soluble solidswere then measured as described below. The materialwas weighed before and after osmodehydration tocalculate the percentage of weight reduction (WR).The moisture content was determined to calculate waterloss (WL) and solids gain (SG), based on the followingequations (Mavroudis et al., 1998):

WRð%Þ ¼ ðWi �WfÞWi

:100 ð1Þ

SGð%Þ ¼ ðWsf �WsiÞWi

:100 ð2Þ

WLð%Þ ¼ SGþWR ð3Þwhere Wi is the initial weight of the sample (g),Wf the final weight of the sample (g), Wsi theinitial total solids content (g) and Wsf the final totalsolids content (g). Each value is the mean of threedeterminations.

Mathematical modelling

Peleg’s equation parameters were obtained using eqn 4(Peleg, 1988). This two-parameter model was redefinedby Palou et al. (1994) in terms of soluble solids andmoisture content and describes sorption curves thatapproach equilibrium asymptotically.

MCðtÞ ¼MC0 �t

k1 þ k2tð4Þ

where MCðtÞ is the amount of water or solids at theinstant t [g g)1 dry matter (DM)], MC0 is the initialamount of water or solids (g g)1 DM), k1 and k2 arePeleg’s parameters and t is the time (s).The value of the amount of water loss or solids gain at

the equilibrium was then calculated using eqn 5 (Parket al., 2002).

MCeq ¼ limt!1ðMC0 �

t

k1 þ k2tÞ ¼MC0 �

1

k2ð5Þ

Pomegranate seeds do not have a spherical shape,Alvarez et al. (1995) pointed out that diffusion problemfor any geometry can be reduced to the analyticalsolution corresponding to a sphere, by modifying theFourier numberF0 ¼ Deff t=R2 , using shape factor.In order to determine the water and solutes effective

diffusion coefficient the following assumptions consid-erations were taken into account: homogeneous body,the external resistance to mass transfer is negligiblecompared with internal resistance, the initial moisture

Osmotic dehydration of pomegranate seeds B. Bchir et al. 2209

� 2009 The Authors. Journal compilation � 2009 Institute of Food Science and Technology International Journal of Food Science and Technology 2009

content was uniform throughout the sample, and thediffusion coefficient is constant (Crank, 1975).The solution for Fick’s equation law for diffusion out

a sphere is given by eqn 6, with using the followingboundary conditions of internal resistance (Crank, 1975;Alvarez et al., 1995):

Uniforme initial amount: t = 0, 0� r�R,MC(t)¼MC0

Symmetry of concentration: t � 0; r ¼ 0;@MCðtÞ@r

¼ 0

Equilibriumcontent at surface: t �0;r¼R;MCðtÞ¼MCeq

WAouS ¼MCðtÞ �MCeq

MC0 �MCeq¼X1n¼1

Bn exp �l2nF0

� �ð6Þ

where Bn = 6 ⁄ln2; ln = nP; F0 = Deff, AorS t ⁄R2;

n = 1, 2, 3,… where Deff, AorS is the effective diffusivityof water loss or solids gain (m2 s)1); n is the number ofseries terms, R is the equivalent radius of sphere (m), r isthe distance in the radius direction (m), and t is the time(s). WA and WS are the dimensionless amount of waterloss and solids gain, respectively; MCeq is the equilib-rium amount of water loss or solids gain (g g)1 DM)calculated using eqn 5.As stated earlier, in this work pomegranate seeds

were assumed to be ellipsoids, having three character-istic diameters (2rM1�2rM2 £ 2RM). According toAlvarez et al. (1995) the shape factor (Y) eqn 7 isdefined as Ss ⁄Sp, and Ss is the surface area of a sphereof volume equal to that of seeds with surface area Sp,which is assumed to be an ellipsoid. The intrinsicdiffusivity Deff is given by Y2 D¢eff. It can beconcluded that the diffusion coefficient calculated fromeqn 6 is D¢eff and that it must be corrected by thefactor Y2 when the product shape can be assumed asan ellipsoid.

w ¼ Ss

Sp¼ 4pR2

e

2pr2 þ 2p rMRMffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1�ðrM=RMÞ2p� �

sin�1ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1� ðrM=RMÞ2

q

ð7ÞPhysico-chemical analysis of seeds

All analytical determinations were performed in tripli-cate. Values were expressed as the mean ± standarddeviation.The dry matter was calculated according to AOAC

(1995). Approximately, 5 g of seeds were oven dried at103 �C ± 2 �C, until constant weight.Total nitrogen was determined by the Kjeldahl

method. Protein was calculated using the general factor(6.25) (AOAC, 1995).

To determine total lipid content, about 5 g of seedswere mixed with chloridric acid. Fat was then extractedwith a soxtherm automatic S 306 AK solvent extractorequipped with six Soxhlet posts (Gerhardt soxtherm,Switzerland) and command unit (Gerhardt Variostat,Switzerland) using petroleum ether 40–60 �C in eachSoxhlet post. The result was expressed as the percentageof lipids in the dry matter.To determine ash content, about 5 g of seeds were

incinerated in a muffle furnace (type Gelman, Germany)at about 550 �C for 8 h. The total ash content wasexpressed in dry weight percentage (AOAC, 1995).Carbohydrate content was estimated by difference of

mean values, 100-(Sum of percentages of moisture, ash,proteins and lipids) (AOAC, 1995).aw was measured using an aqualab (Switzerland)

instrument at 20 �C.The soluble solids of seeds were determined according

to AOAC (1995) methods. It was measured by anATGO digital refractometer (DBX-55, Switzerland) at20 �C and expressed in �Brix.pH measurements were performed using a Hanna

instrument 8418 pH meter (Switzerland) at 20 �C.The CieLab coordinates (L*, a*, b*) were directly

read with a spectrophotocolorimetre Mini Scan XE(Germany) with a lamp (D 65). In this coordinatesystem, the L* value is a measure of lightness, rangingfrom 0 (black) to +100 (white), the a* value rangesfrom –100 (greenness) to +100 (redness) and the b*value ranges from –100 (blueness) to +100 (yellowness).Conductivity was measured using a conductimeter

(LF 597-5; Germany) instrument at 20 �C.Absorbance was measured using a spectrophotometer

(Shimadzu UV 240, Cambridge, USA) and the wavelength used (k) was between 200 and 700 nm.Differential scanning calorimetry (DSC) was per-

formed on the pulp previously separated from pip. A2920 TA Instruments (New Castle, DE, USA) with aRefrigerated Cooling Assessory and modulated capabil-itywas used. The cell was purgedwith 70 mL min)1 of drynitrogen and calibrated for baseline on an empty oven andfor temperature using two temperature and enthalpystandards (indium, Tonset: 156.6 �C, DH: 28.7 J g)1;eicosane, Tonset: 36.8 �C, DH: 247.4 J g)1). Specific heatcapacity (Cp) was calibrated using a sapphire. The emptysample and reference pans were of equal mass towithin ± 0.10 mg. Differential scanning calorimetrycurves were recorded during heating from –50 to 40 �Cat a scan rate of 5 �C min)1. All these DSC experimentswere made using hermetic aluminium pans. The analysedsample mass was about 3.50 ± 0.25 mg.

Statistical Analysis

Statistical analyses were carried out using a statisticalsoftware program (spss for windows version 11.0). The

Osmotic dehydration of pomegranate seeds B. Bchir et al.2210

International Journal of Food Science and Technology 2009 � 2009 The Authors. Journal compilation � 2009 Institute of Food Science and Technology

data were subjected to analysis of variance using thegeneral linear model option (Duncan test) to determinesignificant differences between samples (P < 0.05).

Results and discussion

Chemical composition of pomegranate seeds beforeosmotic dehydration is shown in Table 1. Pomegranateseeds are rich in carbohydrate (�85%) followed byprotein (�8%), lipid (�5%) and Ash (�3%). Thiscomposition is quite similar to pomegranate seedscultivated in Egypt (El-Nemr et al., 1990).As in previous works, three different parameters were

followed during osmotic dehydration: water loss (WL),solids gain (SG) and weight reduction (WR). They wereresponsible for total mass change, shrinkage andchanges in the fruit liquid phase concentration thatdefines the water activity, the quality and the stability ofthe final product (Kowalska & Lenart, 2001; Faladeet al., 2007).

Osmodehydration using sucrose solution

Mass transfer kineticsThe effect of dehydration time on WL, WR, and SG wasstudied in pomegranate seeds at different temperatures(30, 40 and 50 �C). The most significant changes tookplace during the first 20 min of dewatering as shown inFig. 1a. During this time, WL in seeds was 37, 39 and46%, respectively, for 30, 40 and 50 �C. After thisperiod of dehydration, the percentage of water lossvaried slightly and ranged on average close to 35, 38 and43% for 30, 40 and 50 �C, respectively. The same trendwas also observed for WR (Fig. 1b). Under the sameconditions, SG was also increased significantly duringthe first 20 min (Fig. 1c) reaching 5.4, 6.9 and 7.2%respectively for 30, 40 and 50 �C, and tend to be stableat the end of the process. A similar curve has beenreported in the osmotic dehydration of watermelon(Falade et al., 2007). Statistical analysis showed thatWL, SG and WR varied significantly with time. How-ever, the significant difference founded at course of timewas not higher. This fact could be because the majorityof the transfer was done during the first 20 min of the

process. As consequence we suggest to stop the processafter 20 min as it implies no addition of thermal energyto the system.The rapid loss of water in the beginning at various

temperatures (30, 40 and 50 �C) is due to the largeosmotic driving force between the dilute sap of seedsand the surrounding hypertonic medium. Then, slowerwater transfer is mainly influenced by the reduction ofthe difference in concentration between the seeds andosmotic solution which could involve a slower drivingforce. Indeed, the reverse trend of �Brix observed inseeds and osmotic solution confirms these facts(Table 2). The trend observed in SG for the differenttemperatures studied (Fig. 1c) could be explained bymigration of sucrose to the seeds through their cellmembranes due to the important gradient of sugarbetween the seeds and the osmotic solution.From the results shown in Fig. 1, it can be concluded

that the increase of temperature from 30 up to 50 �Clead to an increase of water loss, weight reduction, andsolids gain. The increases of temperature at 40 �C

Table 1 Chemical characteristic of pomegranate seeds

Seeds

Dry matter (DM %) 16.00 ± 0.05

Protein g ⁄ 100 g DM 7.79 ± 0.86

Lipid g ⁄ 100 g DM 4.55 ± 0.40

Ash g ⁄ 100 g DM 2.87 ± 0.19

Carbohydrate g ⁄ 100 g DM 84.93 ± 0.25

pH 4.17 ± 0.20

aw 0.989 ± 0.002

�Brix 15.50 ± 0.09

05

101520253035404550(a)

(b)

(c)

0 20 40 60 80 100 120

Time (min)

% W

L

30 °C 40 °C 50 °C

30 °C 40 °C 50 °C

30 °C 40 °C 50 °C

0 20 40 60 80 100 1200

5

10

15

20

25

30

35

40

45

Time (min)

% W

R

0 20 40 60 80 100 1200

2

4

6

8

10

12

Time (min)

% S

G

Figure 1 Variation of water loss (WL) (a) weight reduction (WR) (b)

and solids gain (SG) (c) with time and temperature (30, 40, 50 �C)using sucrose solution during osmotic dehydration.



involved the same evolution of WL as using 30 �C.However a significant difference was found in compar-ing to 30 �C from time superior to 60 min. At 50 �Csignificant difference was already observed after 20 min.A similar evolution for WR and SG as function of timeand temperature was found. Nevertheless, the increaseof temperature to 40 and 50 �C showed a significantdifference of SG compared to 30 �C from 20 min. Ahigher value of different parameters was alwaysobserved using 50 �C. As consequence we suggest using50 �C to have the best dehydration. Ferreari & Hubin-ger (2008) showed that the increase of temperature leadsto irreversible damage and a loss of selectivity of cellmembrane involving a higher osmotic pressure at theproduct ⁄ solution interface. Moreover, higher tempera-ture raised diffusion coefficients indiucing higher masstransfer rates (Table 3). This behavior has also beenreported in the osmotic dehydration of apricots (Khoyi& Hesari, 2007) and melon (Ferreari & Hubinger, 2008).In this study, the increase of temperature had a more

significant effect on WL than on SG (Fig. 1a and c).Indeed, after 120 min when the temperature increasedfrom 30 to 40 �C, the gain of WL and SG was 4.4% and0.5%, while when the temperature raised from 40 �C to50 �C, the gain was 5.7% and 1.1%, respectively. Inaddition effective diffusivity of water was also higher

than that of the solids (Table 3). This effect is generallyattributed to the influence of natural tissue membranesand to the diffusive properties of water and solutes as afunction of their respective molar mass (Falade et al.,2007). In a study on osmotic dehydration of modelfoods (aqueous agar-agar gels), Raoult-Wack et al.(1989) suggested that this apparent contradiction couldbe due to a reciprocal influence between the water andsolute transfers where sugar penetration by diffusionand sugar release within the water out flow arecombined.

Evaluation of the Peleg and Fick mathematical modelsThe Peleg’s equation parameters (K1 and K2) weredetermined for water loss and solids gain (eqn 5), asshown in Table 4. This model showed a good fit to theexperimental data, with correlation coefficients (R2)close to 0.99. The parameters K1 and K2 did not exhibita clear trend with the increase in temperature. Ferreari& Hubinger (2008), Khoyi & Hesari (2007) and Parket al. (2002) verified the same fact in similar studies withmelon, apricots and pears, respectively, using sucrose asthe osmotic agent.Table 3 shows the effect diffusivity values for water

and solids calculated using Fick’s model (eqn 6), whichalso presented a good fit to experimental data, showing

Table 2 Evolution of osmotic dehydration parameters in sucrose solution at different temperatures 30, 40, and 50 �C

30 �C

0 min 20 min 40 min 60 min 80 min 100 min 120 min

�Brix of solution 55.00 ± 0.00a 51.10 ± 0.63b 49.80 ± 0.10b 49.10 ± 0.70b 49.40 ± 0.10b 49.40 ± 0.20b 49.30 ± 0.20b

�Brix of seeds 15.50 ± 0.09a 39.55 ± 0.63b 42.85 ± 0.07c 44.55 ± 0.07d 45.10 ± 0.28d 46.25 ± 0.07e 46.60 ± 0.14e

pH of solution 8.27 ± 0.03a 4.89 ± 0.09b 4.68 ± 0.08c 4.54 ± 0.06cd 4.52 ± 0.04cd 4.48 ± 0.05d 4.46 ± 0.08d

Conductivity of

solution (ls cm)1)

0.90 ± 0.01a 31.75 ± 0.63b 36.05 ± 1.62c 39.80 ± 0.84d 40.80 ± 0.70de 42.20 ± 1.27de 43.20 ± 1.27e

Dry matter of

seeds (%)

16.00 ± 0.05a 39.30 ± 1.30b 41.20 ± 1.40b 45.20 ± 2.60c 45.20 ± 0.10c 46.80 ± 0.70c 48.20 ± 0.10c

40 �C

�Brix of solution 55.00 ± 0.00a 50.00 ± 0.84b 50.40 ± 0.84bc 49.40 ± 0.28cd 49.20 ± 0.14d 49.15 ± 0.12d 49.05 ± 0.14d

�Brix of seeds 15.50 ± 0.09a 40.85 ± 0.07b 43.35 ± 0.21c 45.40 ± 1.31e 45.60 ± 1.13e 45.85 ± 0.35e 46.85 ± 0.63e

pH of solution 8.27 ± 0.03a 4.70 ± 0.04b 4.50 ± 0.02bc 4.46 ± 0.09c 4.42 ± 0.17c 4.43 ± 0.12c 4.40 ± 0.04c

Conductivity of

solution (ls cm)1)

0.90 ± 0.01a 33.00 ± 1.83b 37.35 ± 1.76bc 40.60 ± 2.97cd 43.95 ± 3.74d 42.15 ± 2.89cd 44.00 ± 1.27d

Dry matter of

seeds (%)

16.00 ± 0.05a 40.90 ± 2.97b 44.20 ± 0.18bc 45.90 ± 1.02c 47.30 ± 0.15c 47.80 ± 0.20c 49.00 ± 0.06c

50 �C

�Brix of solution 55.00 ± 0.00a 49.70 ± 0.07b 49.30 ± 0.01bc 49.10 ± 0.21c 48.90 ± 0.28c 49.00 ± 0.21c 49.00 ± 0.21c

�Brix of seeds 15.50 ± 0.09a 41.60 ± 0.14b 45.30 ± 0.14c 46.40 ± 0.14d 46.90 ± 0.14d 48.70 ± 0.28e 49.10 ± 0.07e

pH of solution 8.27 ± 0.03a 4.60 ± 0.27b 4.50 ± 0.20b 4.50 ± 0.01b 4.40 ± 0.02b 4.30 ± 0.10b 4.30 ± 0.07b

Conductivity of

solution (ls cm)1)

0.90 ± 0.01a 35.50 ± 0.35b 39.00 ± 1.06c 40.10 ± 0.07de 40.50 ± 0.21e 41.00 ± 0.49e 41.20 ± 0.28e

Dry matter of

seeds (%)

16.00 ± 0.05a 42.70 ± 0.08b 46.80 ± 0.65c 47.80 ± 0.83cd 48.30 ± 0.41cde 48.60 ± 0.73de 49.50 ± 0.76e

All values given are means of three determinations. Means in line with different letters are significantly different (P < 0.05)



an average correlation coefficients (R2) close to 0.99. Theexperimental values for effective diffusivity were to anorder of magnitude between 4 · 10)12 to 9 · 10)12 forsolids gain and 5 · 10)12 to 9 · 10)12 m2 s)1 for waterloss. Park et al. (2002) working with pear cubes foundthat Deff ranged from 0.35 · 10)9 to 1.92 · 10)9 m2 s)1

for water loss and from 0.20 · 10)9 to3.60 · 10)9 m2 s)1 for solids gain at different tempera-ture (40–60 �C). Lazarides et al. (1997) found valuesranging from 1.42 · 10)10 to 4.69 · 10)10 for moisturediffusivity and from 0.73 · 10)10 to 2.41 · 10)10 m2 s)1

solute diffusivity of apple slices at different temperature(20–50 �C) and sucrose solution concentrations (45–65%). So, a comparison of the diffusivities values tothose reported in the literature showed that our resultswere lower. This comparison should however take intoaccount the experimental conditions, the different esti-mation methods employed, the variation in food com-position and its physical structure. Indeed, given theirsmall size, pomegranate seeds can be kept intact and donot need to be cut. On the contrary, pear, apple or kiwis,due to their large sizes, have to be cut in small volumes.Thus, cutting these fruits creates more externals lesionleading to a higher contact of cells with the osmoticsolution in a shorter time inducing a higher diffusion.

Physico-chemical Characteristics of the osmodehydratedfruit preparationThe changes that occurred in pomegranate seeds and inthe osmotic solution, a function of time and tempera-ture, are shown in Tables 2 and 5. As it was expected allparameters (�Brix, pH, conductivity, etc.) evolved in thesame trend like mass transfer parameters (WL, SG,WR). In fact, statistical analysis shows a significantdifference (P < 0.05) at the beginning of the process(20 min). The increase of temperature showed that50 �C gave the lowest �Brix, and pH of the solution,and the highest �Brix in the seeds. At the beginning ofthe process (20 min) the �Brix in the solution decreasedas the �Brix of seeds increased, after that �Brix tendedtowards an equilibrium (Table 2). This was a conse-quence of osmosis, inducing a balance of concentrationbetween the seeds and the sucrose solution. The diffu-sion of some solutes from pomegranate seeds to theaqueous solution, could explain the decrease of pH andthe increase of the conductivity in the osmotic solution.The measure of colour parameters L*, a*, b* showed aslight reduction of L* and a slight increase of a* and b*(Table 5). This variation could be explained by amigration of pigment from pulp to solution. Indeedabsorbance reached a peak at 510 nm. According to the

Table 3 Water and solids effective diffusivities

calculated by Fick’s model

Sugar T (�C)

Water loss Solids gain

Deffw (m2 s)1) R2 (%) Deffs (m2 s)1) R2 (%)

Sucrose 50 �C 9.44 · 10)12 99.92 4.81 · 10)12 99.72

40 �C 8.09 · 10)12 99.89 4.72 · 10)12 99.88

30 �C 7.43 · 10)12 99.66 4.21 · 10)12 99.80

Sucrose ⁄glucose

50 �C 9.10 · 10)12 99.93 5.44 · 10)12 99.92

40 �C 7.88 · 10)12 99.77 4.54 · 10)12 99.89

30 �C 6.98 · 10)12 99.77 4.48 · 10)12 99.87

Glucose 50 �C 8.74 · 10)12 99.83 9.54 · 10)12 99.88

40 �C 6.69 · 10)12 99.68 6.52 · 10)12 99.89

30 �C 5.41 · 10)12 99.65 4.94 · 10)12 99.50

Table 4 Values of Peleg’s equation parame-

ters for water loss and solids gain

Sugar T (�C)

Water loss Solids gain

k1 k2 R2 k1 k2 R2

Sucrose 30 37.8782 0.2362 0.9993 15.8206 0.0300 0.9988

40 36.1447 0.2316 0.9999 13.4587 0.0302 0.9996

50 28.0531 0.2317 0.9999 12.0808 0.0286 0.9992

Glucose 30 62.8484 0.2328 0.9999 12.6530 0.0308 0.9967

40 44.9577 0.2315 0.9995 8.9232 0.0360 0.9997

50 25.5221 0.2346 0.9999 4.8449 0.0299 0.9997

Sucrose ⁄glucose

30 44.4009 0.2301 0.9999 13.6050 0.0289 0.9995

40 34.7331 0.2317 0.9998 13.6054 0.0288 0.9995

50 29.7106 0.2311 0.9998 10.5526 0.0286 0.9998



literature, this peak corresponded to the pink pigmen-tation (flavonoids) in pomegranate seeds (Sestili et al.,2007). Table 6 shows that water activity was reducedfrom 0.989 to 0.903, confirming water loss during theprocess. Moreover, using 50 �C involved the lowestwater activity (0.903) compared to the other tempera-tures (30 �C: 0.925 and 40 �C: 0.915). Therefore, wateractivity is very temperature and time dependent.

Thermal properties of seeds as measured by differentialscanning calorimetryOsmotic dehydration of pomegranate seeds was investi-gated by DSC to determine the kinetic of seeds dehydra-tion and the state of water during the process at 50 �C.DSC thermograms (Fig. 2) presented two main thermalevents between )50 �C and 30 �C. The first was a changein heat capacity (DCp) and the secondwas an endothermicpeak. DCp can be related to a freeze-concentration glasstransition temperature (Tg¢) due to the presence ofsucrose, protein, fibre (pectin, lignin, hemicellulose andcellulose), and water in the sample. As reported in suchproducts, carbohydrates and proteins can be described asamorphous food polymers constituent by not arrangedchains (Roos, 1995). The endothermic transition could beattributed to the melting of crystallised water (free andfreezing bound water). In fact, during the cooling onlyfree water and freezing bound water were crystallised togive ice. And during the heating, frozenwater undergoes afusion of ice and unfreezable water does not undergo anychange.The endothermic transition was used to calculate the

amount of unfreezable water (UFW) estimated asfollows:

UFW ¼Wwater � ðDHsample=DHwaterÞDM

ð8Þ

where DHsample is the heat of melting expressed in J ⁄g,DHwater is the normalised heat of melting of pure water

(351.2 ± 1.2 J ⁄g), Wwater is the total water content ofsample expressed in g of water and DM is the dry mattercontent expressed in g DM (Goni et al., 2007).A considerable increase in Tg¢ was observed up to

20 min and after this period Tg¢ varied much slower

Table 5 CieLab coordinates of sucrose solution at different temperatures 30, 40, and 50 �C

CieLab

coordinate

30 �C

0 min 20 min 40 min 60 min 80 min 100 min 120 min

L* 65.76 ± 0.01a 63.04 ± 1.04ab 61.41 ± 2.05b 60.18 ± 2.04b 61.33 ± 1.47b 61.00 ± 2.12b 60.13 ± 0.62b

a* –0.60 ± 0.02a 0.54 ± 0.07b 1.35 ± 0.42c 3.44 ± 0.29e 2.29 ± 0.38d 3.44 ± 0.16e 3.15 ± 0.49e

b* 3.60 ± 0.01a 6.78 ± 0.15c 5.92 ± 0.58bc 6.25 ± 0.68bc 5.95 ± 0.35bc 5.44 ± 0.08b 6.79 ± 0.36c

40 �CL* 65.76 ± 0.01a 59.64 ± 1.73bc 59.58 ± 0.49bc 60.96 ± 1.05b 59.33 ± 0.58bc 57.47 ± 0.03c 58.76 ± 0.65c

a* -0.60 ± 0.02a 3.82 ± 0.34c 4.62 ± 0.70c 2.31 ± 0.02b 4.58 ± 0.73c 5.81 ± 0.27d 6.56 ± 0.15d

b* 3.60 ± 0.01a 4.38 ± 0.36ab 4.85 ± 0.63ab 5.70 ± 0.57bc 6.27 ± 0.891bc 7.01 ± 0.08de 8.18 ± 1.55e

50 �CL* 65.76 ± 0.01a 61.40 ± 0.96b 60.90 ± 0.40b 60.50 ± 0.47bc 59.80 ± 0.75bc 59.60 ± 1.32bc 58.80 ± 0.15c

a* -0.60 ± 0.02a 2.40 ± 0.92b 2.90 ± 0.134bc 3.30 ± 0.46bcd 4.10 ± 0.30cd 3.70 ± 1.14bcd 4.60 ± 0.24d

b* 3.60 ± 0.01a 6.50 ± 0.26b 7.80 ± 0.07bc 8.10 ± 0.17bc 9.60 ± 1.98c 8.90 ± 0.04c 9.30 ± 0.09c

All values given are means of three determinations. Means in line with different letters are significantly different (P < 0.05)

Table 6 Differential scanning calorimetry results for pomegranate

seeds over soaking time in sucrose, glucose and mixture sucrose and

glucose solution at 50 �C

Time

(min)

Tg¢ (�C)

midpoint

Tf (�C)

onset

DHfus

(J g)1)

Unfreezable

water

(g g)1 DM) aW

Sucrose solution

0 –41.88 0.22 233 3.98 0.989a

20 –34.19 –4.90 93.86 1.09 0.954b

40 –33.64 –5.65 81.17 0.91 0.946c

60 –33.61 –5.92 79.02 0.88 0.942c

80 –34.43 –8.84 58.74 0.92 0.923d

100 –35.35 –9.48 47.52 0.92 0.905e

120 –34.87 –8.56 61.33 0.85 0.903e

Sucrose and glucose solution

0 –41.88 0.22 233 3.98 0.989a

20 –35.39 –7.43 78.88 1.08 0.958b

40 –35.62 –6.49 83.20 0.96 0.945c

60 –35.42 –7.78 70.04 0.94 0.931d

80 –35.50 –7.36 76.19 0.88 0.919e

100 –34.74 –7.39 75.47 0.84 0.910ef

120 –35.03 –6.92 82.96 0.80 0.906f

Glucose solution

0 –41.88 0.22 233 3.98 0.989a

20 –40.65 –8.32 83.99 1.25 0.956b

40 –40.03 –10.04 82.87 0.93 0.947b

60 –40.65 –10.92 72.74 0.95 0.930c

80 –40.08 –11.25 70.43 0.89 0.925c

100 –40.87 –11.42 67.22 0.90 0.911d

120 –40.60 –11.88 65.20 0.93 0.910d

Means in column with different letters are significantly different

(P < 0.05)



and reached –34.87 �C at the end of the process(Table 6). Moreover melting point (Tf), unfrozen water(UFW) and enthalpy of fusion (DHfus), stronglydecreased during the first 20 min and after this time,Tf and DHfus showed a slight decrease but UFWtended to be constant for the rest of the process. Asimilar evolution was observed by Cornillon (2000)using apple soaked in 63 g sucrose ⁄100 g solution forosmotic dehydration.The increase of the glass transition (Tg¢), the lower

enthalpy of fusion (DHfus) and water activity (aW) wereconsistent with the fact that less and less water waspresent in the seeds as the dehydration process occurred(Cornillon, 2000). Sa et al. (1999) found that Tg¢ forpolysaccharides water systems reach to a maximum withdecreasing water content, inducing the decreased mobil-ity of the polymer chains. Indeed, it is well known thatwater has a negative Tg¢ ()173 �C) as opposed to thedifferent constituents of seeds that have a positive Tg¢(sucrose: 62 �C; pectin: 160 �C; hemicellulose: 150–220 �C; cellulose 220–250 �C; protein: 77–112 �C)(Roos, 1995). Thus, the presence of water permits toreduce the Tg¢ of sample. It is well know establish thatwater drastically decreased the Tg¢ of food, due to itsplasticising effect on amorphous polymers (Roos, 1995).A comparison with published literature data on water–sucrose solutions and Tg¢ seeds (at the end of theprocess) showed close values, indicating that sucrosewas predominant in seeds. In fact Tg¢ of a sucrosesolution (49�Brix) and Tg¢ of seeds (also 49�Brix), at theend of the process, were respectively –32.21 and –34.87 �C. It is well known establish previously thatdiffusion of sucrose in the seeds induced an increase ofTg¢ (Sa et al., 1999). Moreover pomegranate seedspresent a decrease of freezing temperature, which canbe explained by the depressing effect of solute, such as

sugars, diffusing in the seeds. Indeed, several worksreported that the increase of solutes in fruits was closelyrelated to the decrease of the freezing temperature(Ohkuma et al., 2008). The increase of the relativeamount of sucrose and the reduce amount of water inthe cell corresponded to the shift of Tg¢.On analyzing the DSC data, we observed that the

amount of unfreezable water (water that did not freeze)declined in the beginning of the process from 3.98 to1.09 g g)1 DM and tended to stabilise in the course oftime reaching � 0.90 g g)1 DM. This fraction is stronglyassociated with the polymer matrix and showed neitherexothermic nor endothermic peak on DSC curves. Thedecrease of UFW in seeds could be due to the higherpercentage of water loss at the beginning of the process.In fact, dry matter increased from 16% to 43% min andwater activity decreased from 0.989 to 0.954 at 50 �Cafter 20 min. The stability of UFW was the result ofwater loss and solids gain, and implicate that waterbecome more bound in seeds. Moreover, the analyzing ofthe % of frozen water (calculated by dividing theenthalpy of fusion of sample by the enthalpy of fusionof pure water) and the % of UFW (calculated bysubtracting the % of total water per the % of frozenwater) showed different evolution in course of time. Infact, the % of frozen water decreased 3.5 times contrarythe % of UFW that increased 2.5 times. This was aconsequence of water loss and sugar gain during theprocess. Many authors found that the increase in theunfreezable water weight fraction in fruit can mainly beattributed to a significant accumulation of osmolitessuch as soluble sugars (Goni et al., 2007; Ohkuma et al.,2008). Moreover, the most significant changes took placeduring the first 20 min of the process, that confirmingprevious results. During this time, the % of frozen waterdecreased from 70% to 28%, whereas the % of UFWincreased from 14% to 29%. After this period, the % offrozen water and UFW slightly varied and ranged onaverage close to 20% and 34%, respectively. The sametrend was also observed for water activity indicating thatless and less free water was available in seeds. The finalproduct presented a higher % of UFW than % of frozenwater; this is an advantage for a better conservation ofseeds. Nevertheless, water activity of osmodehydratedseeds was higher (superior to 0.9) involving certainundesirable reactions, such as non-enzymatic browning,fat oxidation, vitamin degradation, enzymatic reactions,and protein denaturation. As a consequence, othertreatments (pasteurisation, freezing, drying) will benecessary to ensure a good conservation of the seeds.

Osmodehydration using glucose and mixture sucrose andglucose solution

Using glucose and mixture sucrose and glucose solutiontime and temperature had a similar effect on different

Time: 20 min AW: 0.954




Time: 100 min AW: 0.905

Time: 120 min AW: 0.903

–1.2

–1.0

–0.8

–0.6

–0.4

–0.2

0.0

0.2H

eat f

low

(W

g–1

)

–60 –40 –20 0 20 40

Temperature (°C)Exo up Universal V3.0G TA Instruments

Figure 2 DSC thermogram obtained for pomegranate seeds soaked

in sucrose solution at 50 �C.



parameters (WL, SG, WR, Deff, �Brix, DM, pH, etc.) aswith the sucrose solution. With regard to the kind ofsolute employed, comparing the values of WL, SG andDeff at the same temperature, osmotic dehydration withglucose leads a decrease of water loss and a slightlyincreased solids gain (Fig. 3a and b). Moreover thedifference on �Brix between seeds and solution was veryweak using glucose solution. In addition glucose solu-tion induces a lower Deff of water and a higher Deff ofsolids contrary to sucrose solution (Table 3). Figure 3ashows that the sucrose solution allowed a better waterloss followed by the sucrose ⁄glucose mix and the glucosesolution. These dissimilarities were attributed to thespecific surface of seeds and the differences betweenmolecular weight of glucose and sucrose. In fact, masstransport can be described by the Fick’s second Law,depending on the coefficient (Deff) which is influenced bythe radius of solute (Saurel et al., 1994). Briois et al.(1998) showed that the speed of diffusion of sugarmolecules in fruit membrane cells was negatively corre-lated with their molecular size. Indeed with a low molarmass (glucose) solute, the effect of dilution was respon-sible for the faster reduction of the difference in averageconcentration between liquid phase and solid phase,inducing decrease of the water loss in the course of time.As consequence glucose allowed easily diffusion(Masmoudi et al., 2007).

Tf, DHfus, aW and UFW evolve in the same way aswith the sucrose solution except the Tg¢ for glucose seedsthat slightly increase as a function of time (Table 6). Asit was shown in sucrose solution in this case, Tg¢ ofwater-glucose and seeds (at the end of the process)showed close values, indicating that glucose was pre-dominant in seeds. In fact Tg¢ of a glucose solution(55�Brix) and Tg¢ seeds, at the end of the process, wererespectively –40.6 and –44.9 �C. Roos (1995) and Liuet al. (2007) showed that Tg¢ was strongly dependent onthe molecular weight, it decreased with decreasingmolecular weight. Table 6 shows that the addition ofsmall molecules decreased the value of Tg¢. In fact, theuse of a glucose solution showed the lowest Tg¢and Tf.Thus glucose solution induces reducing of water losscompared to the others osmotic solution. Roos (1995)found that higher sucrose content in the mix induced ahigher Tg¢. Table 6 shows that the amount of UFW atthe end of the process was very closed. In fact, UFWvaried between 0.80 and 0.93 involving the presence ofvery tightly bound water to the sample, which is verydifficult to eliminate with this process even after120 min.

Conclusion

Osmotic dehydration process could be used for theconservation of pomegranate seeds. The rate of differentparameters was directly related to temperature, time,and solute. In fact process showed that operating 20 minat 50 �C offered the best result. As a consequence, itcould be better to stop the process after 20 min as itimplies no addition of thermal energy to the system.Osmotic dehydration reduced water activity from 0.989to an average of 0.900. At this aW value a complemen-tary treatment such as drying, frozen and pasteurisationshould be necessary to ensure its good conservation.The nature of sugar used for the dehydration solution

involves modifications in the evolution of mass transfersand effective diffusivity during the process. In fact,sucrose (higher molecular weight) induced the besteffective diffusivity of water involving the best dehydra-tion of seeds, contrary to glucose (lower molecularweight) that induced the best effective diffusivity ofsolids and than impregnation. Therefore we suggestusing sucrose solution to have the best dehydration. Onthe other hand, the study of physico-chemical charac-teristics of osmodehydrated pomegranate seeds showedthe lost of solutes from the seeds to the osmotic solutionduring the osmotic dehydration process. So thesesolutions could be used as natural additives (flavourand colour) in the industry.Differential scanning calorimetry data provide com-

plementary information on the mobility changes ofwater and solute in osmotically dehydrated pomegran-ate seeds. Indeed, it was possible to determine a strong

0

5

10

15

20

25

30

35

40

45

50(a)

(b)

0 20 40 60 80 100Time (min)

120

% W

L

Sucrose Glucose Sucrose/Glucose

0 20 40 60 80 100 1200

2

4

6

8

10

12

14

Time (min)

% S

G

Sucrose Glucose Sucrose/glucose

Figure 3 Comparison of water loss (WL) (a) and solids gain (SG)

(b) using different osmotic solutions (sucrose, glucose and

mixture sucrose and glucose) at 50 �C.



decrease in water mobility involving an increase of glasstransition as more solute and water migrated respec-tively into and out of seeds. It also appeared that Tg¢depends on the types of sugar. In fact Tg¢ of seeds usinga sucrose solution was higher than Tg¢ using glucose orglucose ⁄ sucrose mix solution. After osmotic dehydra-tion, the product presented a higher % of UFW than %of frozen water, this is an advantage for a betterconservation of seeds.The finished product has an attractive colour and

presents a good texture in mouth, a pleasant sugar tasteand a good aroma. It would be interesting for thecontinuation of this work to assess the sensory proper-ties (texture, flavour, etc.) and to substitute the standardsolutions by new solutions (date juice) that bring neworganoleptic properties to the finished product.

References

Adsule, N.R. & Patil, N.B. (1995). Pomegranate. In: Handbook ofFruit Science and Technologies: Production, Composition, Storageand Processing (edited by D.K. Salunkhe, S.S. Kadam & S. S). Pp.455–463. New York, USA: Marcel Dekker.

Al-Maiman, S.A. & Ahmad, D. (2002). Changes in physical andchemical properties during pomegranate (Punica granatum L.) fruitmaturation. Food Chemistry, 76, 437–441.

Altan, A. & Maskan, M. (2004). Rheological behavior of pomegranate(Punica granatum L.) juice and concentrate. Journal of TextureStudies, 36, 68–77.

Alvarez, A.C., Aguerre, R., Gomez, R., Vidales, S., Alzamora, S.M. &Gerschenson, L.N. (1995). Air dehydration of strawberries: effects ofblanching and osmotic pretreatments on the kinetics of moisturetransport. Journal of Food Engineering, 25, 167–178.

AOAC (1995). Official Methods of Analysis, 15th edn. Arlington, VA,USA: Association of Official Analytical Chemists.

Briois, E., Dusautois, C. & Heno, P. (1998). Applications alimentairesdes sirops de glucose a haute teneur en maltose. IndustriesAlimentaires et Agricoles, 7 ⁄ 8, 79–81.

Cornillon, P. (2000). Characterization of osmotic dehydrated Apple byNMR and DSC. Lebensmittel-Wissenschaft und-Technologie-FoodScience and Technology, 33, 261–267.

Crank, J. (1975). The Mathematics of Diffusion, 2nd edn. Oxford:Clarendon Press.

El-Nemr, E., Ismail, A. & Ragab, M. (1990). Chemical composition ofjuice seeds of pomegranate fruit. Journal of Food Science, 7, 601–606.

Espiard, E. (2002). Introduction a la transformation industrielle desfruits. Pp. 181–182. Paris, France: TEC&DOC-Lavoisier.

Falade, K., Igbeka, J. & Ayanwuyi, F. (2007). Kinetics of masstransfer and colour changes during osmotic dehydration of water-melon. Journal of Food Engineering, 80, 979–985.

Ferreari, C.C. & Hubinger, D.M. (2008). Evaluation of the mechanicalproperties and diffusion coefficients of osmodehydrated meloncubes. International journal of Food Science and Technology, 43,2065–2074.

Goni, O., Munoz, M., Cabello, J., Escribano, M. & Merodio, C.(2007). Changes in water status of cherimoya fruit during ripening.Postharvest Biology and Technology, 45, 147–150.

Ivan, L., Nicholas, J. & Gary, D. (2007). A simple centrifugaldehydration force method to characterize water compartments infresh and post-mortem fish muscle. Cell Biology International, 31,516–520.

Khoyi, M. & Hesari, J. (2007). Osmotic dehydration kinetics of apricotusing sucrose solution. Jouranl of Food Engeneering, 78, 1355–1360.

Kowalska, H. & Lenart, A. (2001). Mass exchange during osmoticpretreatement of vegetables. Journal of Food Engineering, 49, 137–140.

Krokida, M.K., Oreopoulou, V., Maroulis, Z.B. & Marinos-Kouris,D. (2001). Effect of osmotic dehydration pretement on quality ofFrench fries. Journal of Food Engineering, 49, 339–345.

Lazarides, H.N., Gekas, V. & Mavroudis, N. (1997). Apparent massdiffusivities in fruit and vegetable tissues undergoing osmoticprocessing. Journal of Food Engineering, 31, 315–324.

Liu, Y., Bhandari, B. & Zhou, W. (2007). Study of glass transition andenthalpy relaxation of mixtures f amorphous sucrose and amor-phous tapioca starch syrup solid by differential scanning calorim-etry. Journal of Food Engineering, 81, 599–610.

Maestre, J., Melgarejo, P., Tomas, A. & Garcia-Viguer, C. (2000).New food products drived from pomegranate. Cahiers Optionsmediterraneennes, 13, 243–245.

Masmoudi, M., Besbes, S., Blecker, C. & Attia, H. (2007). Preparationand characterization of osmotidehydrated Fruits from Lemon andDate By-products. Journal of Food Science and Technology Interna-tional, 13, 405–412.

Mavroudis, N.E., Gekas, V. & Sjohlm, I. (1998). Osmotic dehydrationof apples, shrinkage phenomena and the significance of initialstructure on mass tranfer rates. Journal of Food Engineering, 38,101–123.

Ohkuma, C., Kawai, K., Viriyarattanasak, C. et al. (2008). Glasstransition properties of frozen and freeze-dried surimi products:effect of sugar and moisture on the glass transition temperature.Food Hydrocolloids, 22, 255–262.

Palou, E., Lopes-Malo, A., Argaiz, A. & Welti, J. (1994). The use ofPeleg’s equation to model osmotic concentration of papaya. DryingTechnology, 12, 965–978.

Park, K.J., Bin, A., Bord, F.P.R. & Park, T.H.K.B. (2002). Osmoticdehydration Kinetics of pear D’anjou (Pyrus communis L.). Journalof Food Engineering, 52, 293–298.

Peleg, M. (1988). An empirical model for the description of moisturesorption curves. Journal of Food Science, 53, 1216–1219.

Raoult-Wack, A.L., Lafont, F., Rios, G. & Guilbert, S. (1989).Osmotic dehydration: study of mass transfer in terms of engineeringproperties. In: Drying. 89th edn (edited by A.S. Mujumdar & M.Roques), Pp. 487–495. New York: Hemisphere Publishing Corpo-ration.

Raoult-Wack, A.L., Guilbert, S., Le Maguer, M. & Rios, G. (1991).Simultaneous water and solute transport in shrinking media.Part 1. Application to dewatering and impregnation soakingprocess analysis (osmotic dehydration). Drying Technnology, 9,589–612.

Roos, Y. (1995). Characterisation of food polymers using statediagrams. Journal of Food Engineering, 24, 339–360.

Sa, M.M., Figueiredo, A.M. & Sereno, A.M. (1999). Glass transitionsand state diagrams for fresh and processed apple. ThermochimicaAct, 329, 31–38.

Saurel, R., Raoult-Wack, A.L., Rios, G. & Guilbert, S. (1994).Approches technologiques nouvelles de la deshydrataion-impregna-tion par immersion. Cahier Scientifique, 112, 543–550.

Sestili, P., Martinelli, C., Ricci, D. et al. (2007). cytoprotection effectof preparations from various parts of Punica granatum L. fruits inoxidatively injured mammalian cells in comparison with theirantioxidant capacity in cell free systems. Pharmacological Research,56, 18–26.

Storey, T. (2007). La grenade le fruit medicament, Magazine NEXUS.Sante, 51, 46–54.

Torreggiani, D. & Bertolo, G. (2001). Osmotic pre-treatments in fruitprocessing: chemical, physical and structural effects. Journal of FoodEngineering, 49, 247–253.

Vivanco, P.D., Hubinger, M.D. & Sobral, P.J.A. (2004). Mass transferin osmotic dehydration of Atlantic Bonito (Sarda) fillets undervacuum and atmospheric pressure. International Drying Symposium,14, 2105–2112.



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