Effect of air drying on quality characteristics and mass transfer kinetics of osmotically dehydrated sea buckthorn by stevia

Sea buckthorn is ranked among the most significant super foods worldwide. Its fruits and leaves are used as fresh or dried in food, pharmaceutical and cosmetic industry. As super food any pre-treatment should sustain this property and hence this research was focused on osmotic dehydration of sea buckthorn by stevia also a super food. Therefore, water loss, sugar gain, acidity, ascorbic acid and water diffusivity were evaluated during osmotic dehydration of sea buckthorn by two stevia solutions, 15 and 30Brix and following were air-dried at 50C by comparing the effect of steam blanching per case. Steam blanched samples exhibited increased water loss at the end of the process, 55% at 30Brix and 48% at 15Brix, compared to untreated samples where losses were 43% (30Brix) and 28% (15Brix) respectively. Ascorbic acid was significantly reduced, exceeding 50% in steam blanched samples and 23% in untreated samples. Steam blanched samples dehydrated at 15Brix exhibited 82% dry matter increase and only 39% the untreated samples. Similarly, samples dehydrated at 30Brix exhibited 84% dry matter increase and 53% when no steam blanching was applied. Solid gain was seven times less compared to water loss which is attributed to high molecular weight of steviol glycoside. The osmotic dehydration and airdrying curves were described effectively by Peleg and Fick models, and Logarithmic and Fick models respectively, having in all cases Radj>99% and SEE<0.2. The water diffusivity of steam blanched samples was 3.2-5.57×10 m/s for water loss and 1.272.03×10 m/s for solid gain at 30Brix and 2.12-4.27×10 m/s and 0.91-1.98×10 m/s at 15Brix. Finally, the water diffusivity of steam blanched samples during air-drying was 2.11-2.29×10 m/s and 1.56-1.66×10 m/s in the case of untreated samples.


Introduction
Sea buckthorn (Hippophaes rhamonides L) is among the most important superfoods and is used for its fruits as well its leaves. Its fruits are consumed either as fresh or dried mainly in the pharmaceutical and cosmetic industry. Sea buckthorn has many nutritional benefits as it has been reported to contain more than 190 essential compounds in seeds, pulp, fruit and juice, such as vitamins A, K, C, B1, B2 and E, fatty acids, lipids, organic acids, amino acids, carbohydrates, folic acid, tocopherols, flavonoids, phenols, terpenes and tannins which have beneficial effects on health (Bal et al., 2011).
The composition of sea buckthorn juice varies according to cultivar, growing conditions, harvest time, ripeness and processing technology. Has been found to contain high quantities of ascorbic acid ranging between 28 to 2,500 mg/100 g. The pH of sea buckthorn juice ranges from 2.7 to 3.1 which do not favour ascorbate oxidase activation and therefore ascorbic acid is largely retained during juice processing. The soluble solids content ranges from 7.0 up to 22.7 o Brix. The sea buckthorn juice is characterized by high quantities of various organic acids so its acidity ranges from 3.5 to 7.3% (Zeb, 2004).
Stevia is a natural sweetener used in food and beverage industry as a sugar substitute. A part of stevia is 15 to 30 times sweeter than a part of sucrose (Savita et al., 2004). Stevia plant (Stevia rebaudiana Bertoni) belongs to the family of Compositae or Asteraceae, subfamily of Eupatorieae. Have been identified 280 species to belong at stevia genus but only Stevia rebaudiana has intense sweetening power (Lemus-Mondaca et al., 2012). The stevia plant is a good source of carbohydrates, proteins, fibres, metals, essential and non-amino acids. The physical and chemical characteristics of the extracted stevioside, as well as its thermal and acid stability along with its superior sensorial characteristics, have spread its use in food and beverage industry (Abou-Arab et al., 2010). The objectives of this study were (i) to conduct osmotic dehydration of sea buckthorn maintaining its superior nutritional value adopting an equal nutritional value hypertonic medium, this of stevia, (ii) to evaluate the water loss, sugar gain, acidity, ascorbic acid concentration and water diffusivity of sea buckthorn (var. Chuyskaya) initially osmotically dehydrated in two stevia solutions, 15 ο Brix and 30 ο Brix and then air-dried at 50 ο C by comparing the effect of steam blanching application to each tested case.

Materials and methods
Sea buckthorn fruits (var. Chuyskaya) were supplied from Agricultural Co-operative of Karditsa (Northern Greece). The fruits were transported to the laboratory where defective fruits (injured, overripe, etc) were discarded. Measurements of weight, acidity, soluble solids and ascorbic acid were carried out in two groups of 50 fruits each. In group A, the 50 fruits weighed 38.15 g and in group B, 35.77 g; the total soluble solids was 9.1% and 8.2% respectively; for group A the malic acid was 0.34%, the citric acid, 0.54% and the ascorbic acid, 487.2 ppm while for group B the malic acid was 0.31%, the citric acid, 0.51% and the ascorbic acid, 490.9 ppm. The average initial moisture content was 9.83±0.2 kg w / kg dm and was estimated gravimetrically using a vacuum oven (VD 53, Binder, Germany) at 70°C for 24 hrs (AOAC, 1997).
Four experimental series were osmotically dehydrated at 40°C, two in 30°Brix solutions and two in 15°Brix solutions, and upon completion of osmosis, the samples were air-dried at 50°C. The weight ratio of the osmotic solution to fruit sample was 28:1 (30 o Brix) and 24:1 (15 o Brix) based on Yadav and Singh (2014) review. Since stevia is 15-30 times sweeter than sucrose, a higher dilution ratio was adopted than the one is normally used in sucrose solutions (Yadav and Singh, 2014). The difference between the two experimental series per stevia solution was based on the application or not of steam blanching for 3 mins. In each experimental series 25 g per sample were placed in small perforated pouches and immersed in two stevia solutions. Six replicates were used per experimental series. The samples were osmotically dehydrated for 6 hrs in 750 mL beakers containing the stevia solutions and the samples were weighed in hourly intervals. Upon removal from the osmotic solutions, the samples were drained and the excess of the stevia solution removed with absorbent paper. The solid content of the osmotically dehydrated fruits was determined gravimetrically using a vacuum oven (VD 53, Binder, Germany) at 70°C for 24 hrs (AOAC, 1997). Measurements regarding total soluble solids, acidity and ascorbic acid were conducted in two replicates as follows. The remaining samples were airdried at 50°C until steady weight was achieved. Upon drying, hourly weighing of the samples was carried out. At the end of the air-drying, the acidity, the total soluble solids and the ascorbic acid of the dried samples were evaluated. The dried samples were pulped, diluted with 10 mL of deionised water and filtered so the remaining juice to be used for measurements of the total soluble solids, acidity and ascorbic acid. The geometric mean diameter in terms of Feret diameter was estimated by image analysis employing ImageJ 1.46r image analysis software (Research Services Branch, NIMH, Bethesda, USA). For this purpose, twenty randomly selected sea buckthorn berries were photographed by a digital camera Konica Minolta Dimage Z2 (4.0 Mpixel) and analysed so the mean diameter was measured as 0.707 cm.

Theoretical aspects, water and solute diffusivity estimation
The water adsorption/desorption during osmotic dehydration has been described by theoretical or semitheoretical models. Also, a number of empirical models have been used to solve the diffusion problem. The most employed empirical model in literature (Park et al., 2002;Azoubel and Murr, 2004), for water adsorption/ desorption in foods during osmosis belongs to Peleg (1988), where MC t is the moisture content (kg w /kg dm ) for immersion time t (min), MC o is the initial moisture content (kg w /kg dm ), K 1 is the temperature dependent Peleg constant [h/(kg w /kg dm )] related to dehydration rate at the beginning of the process, and K 2 is Peleg constant (kg w /kg db ) -1 determined by the moisture concentration in equilibrium . The ± sign in Equation 1 corresponds to adsorption (+) and desorption (-) respectively.
Considering sea buckthorn fruit as a sphere of uniform initial water (MC o ) and solids content, the analytical solution of Fick equation for constant process conditions is given by Crank (1975).
Where n is the number of terms taken in the series, D is the effective diffusivity (m 2 /s), t is the process time (s) and r e is the mean geometric radius (m).
Considering the first term (n = 1) of the series (Equation 2) derives an error over 60% (Efremov and Kudra, 2005) at the beginning of the process (F o = 0). The estimation error drops to 4% when 15 terms are considered, whereas 58 terms are needed to achieve error close to 1%. Efremov and Kudra (2005) minimized this error by integrating the correction factor α' (cf. to Equation 3) without considering many terms.
Where F o is the Fourier number. For spherical shape, the correction factor α'=0.83 results in a maximum relative error of ±17%. Equation 3 is solved with respect to D as follows, Mundada et al. (2010) employed the analytical solution of Fick equation to estimate the diffusion coefficient of solid gain, Equation 5, The geometric mean of the diffusion coefficient was estimated for water loss (D WL | avg ) and solid gain (D SG | avg ) during the osmotic dehydration as well as for water loss (D) during the air-drying of the sea buckthorn as follows (Lentzou et al., 2019).

Osmotic dehydration and hot air-drying
The osmotic solutions of stevia used in this study consisted of 500 mL deionised water and 209 g stevia powder, case of 30°Brix solution, and 91 g of stevia powder, case of 15°Brix aqueous solution. Dilution of stevia in the deionised water was carried out by means of a heated magnetic stirrer (RCT basic, IKA-Werke GmbH & Co. KG, Germany) whose heating plate was set to 40°C . To sustain the hypertonic solutions at 40 o C throughout the osmotic process, the beakers containing the osmotic solutions were placed inside a water bath at 40°C and the osmotic solutions in the beakers were agitated in regular intervals.
Weighing of the mass was carried out by an electronic balance (KERN, PCB-440, Japan) having ±0.01 g accuracy. Based on the previous measurements the water loss (Equation 7) and solid gain (Equation 8) were estimated as follows (Panagiotou et al., 1999), Where mₒ, m t are the initial dry matter and the dry matter in any time (kg); M o , M t are the initial mass and the mass in any time (kg); MCₒ, MC t is the initial moisture content and the moisture content in any time (kg w /kg dm ). The water loss (Equation 7) express the diffused water (kg water loss /kg initial mass of fruit ) from the fruit to the osmotic solution due to osmotic pressure deficit between fruit and solution and solid gain (Equation 8) express the diffused solids (kg solids gained /kg initial mass of fruit ) from the osmotic solution into the fruit.
Air-drying of the osmotic dehydrated samples was carried out in an atmospheric drying oven (Heraeus T5028, Thermo Scientific, Austria) at 50°C for 15 hrs. Upon drying completion, dry matter was estimated gravimetrically using a vacuum oven (VD 53, Binder, Germany) at 70°C for 24 hrs (AOAC, 1997). Based on the previous measurements the moisture content MC = (M t -m f )/m f and the moisture ratio MR = MC t / MC 0 were estimated, where m f is the dry mass of the product (kg), M t is the mass of the product at any time (kg), MCₒ and MC t are the initial moisture content and the moisture content at any time respectively (kg w /kg dm ).

Total soluble solids, acidity and ascorbic acid
Measurement of the total soluble solids in the juice of the osmotic dehydrated and the air-dried fruits was carried out by a digital refractometer (SR-400, Japan) having ±0.25°Brix accuracy. The total soluble solids were expressed as g of solid per 100 g of juice (Brix). Measurement of the fruit's acidity in the juice of the osmotic dehydrated and air-dried fruits was carried out by a digital acidity meter (GMK-708, UK) having the accuracy of ±0.05%. Prior to the malic and citric acids measurement, dilution of 0.33 mL of juice into 20 mL of deionised water was carried out. The acidity was expressed in g of malic/citric acid per 100 g of juice.
The ascorbic acid was measured by an automatic titrator (HI902C, HANNA, USA) using a 0.02 N iodine buffer. For the measurement of the ascorbic acid, 15 mL of filtered fruit juice was diluted in a 250 mL beaker adding 100 mL of demineralised water, 8mL of 16% sulphuric acid and 3 g of potassium iodide.

Statistical analysis
Analysis of variance (ANOVA) was carried out to identify significant effects of process parameters employing Statgraphics Centurion XVI (Statpoint Technologies, Virginia, USA) at significance level of P≤0.05. Mean values were subjected to Fisher's Least Significant Difference test (LSD) at P≤0.05. This statistical test is liberal with respect to the comparison wise error rate but is powerful to detect true differences. Nonlinear regression was carried out by the Statgraphics Centurion XVI (Statpoint Technologies, VA, USA) at significance level P≤0.05 employing the Levenberg-Marquardt optimisation algorithm (Mason et al., 2003).

Kinetics of water loss and solid gain
In the osmotic process, two parameters are of great interest, water loss (Equation 7) and solid gain (Equation  8). In most of the cited studies the water loss curves (Figure 1a) exhibit initially a characteristic increase corresponding to high rate of water loss and solid gain followed by a falling rate at the later stages. The high water loss rate and solid gain at the initial stage of osmosis are due to higher osmotic driving forces between the fresh fruit and the surrounding hypertonic medium. The shape of the water loss curves during osmotic dehydration has been extensively reported (Panagiotou et al., 1999;Azoubel and Murr, 2004;Mundada et al., 2010;Ganjloo et al., 2012). Increasing the concentration of the osmotic solution increases the pressure deficit which leads to higher water loss and solid gain although not to the same extent. In most of the cited cases has been reported faster water loss than solid gain (Azoubel and Murr, 2004).
In Figure 1a is presented the water loss during the osmotic dehydration. It is observed that the steam blanched samples exhibited increased water loss, so their final values were 55% and 48% at 30 ο Brix and 15 ο Brix osmotic solutions respectively, compared to untreated samples that were 43% and 28% for the osmotic solutions of 30 o Brix and 15 o Brix, respectively. This response can be attributed to disintegration of the waxy layer of the sea buckthorn epidermis taking place during steam blanching. The previous results are in agreement with those of Araya-Farias et al. (2014), who reported that steam blanching facilitates water loss during osmosis. Panagiotou et al. (1999)  resulted in increased water loss compared to the latter, under the same osmotic solution concentration and treatment duration due to the higher osmotic effect of glucose compared to that of sucrose. The previous osmotic effect was attributed to sucrose's molecular weight (342.3 g/mol) which is approximately twice that of glucose (180.16 g/mol) and results in roughly halfmolecular concentration of sucrose solutions and consequently significantly lower osmotic pressure of the sucrose than the glucose solutions. Steviol glycoside molecular weight is 318.4 g/mol which rank stevia to the same approximately osmotic potential of sucrose. From  Figures 1a and b, it can be seen that solid gain is seven times smaller of water loss. This response can be attributed to the high molecular weight of steviol glycoside that favours water loss at the expense of solid gain as Mundada et al. (2010) explained. On the other hand, Hawkes and Flink (1978) reported that the progressive accumulation of solids during the osmotic dehydration, form a surface layer on the external cellular layer of sea buckthorn, which acts as a barrier against water loss and solid gain.
The Peleg model (Equation 1) was tested for its goodness of fitting water loss experimental data during the osmotic dehydration ( Table 2). The fitting efficiency was very good in all the tested cases as this can be seen from the statistical estimates R 2 adj >99% and SEE<0.2. The fitting efficiency can also be seen in Figure 2 as well as the effect of steam blanching on the final moisture ratio which after 6h of osmotic dehydration was almost 50% less in the case of the steam blanched samples at 30 o Brix compared to those not be steamed blanched at 15 o Brix. The K 1 values for all the tested cases (pre-treatment×solution concentration) are seen in Table 2. The reciprocal of K 1 describes the initial mass transfer rate, e.g., the higher the 1/K 1 the higher the mass transfer rate. Based on the 1/K 1 values it is seen that as the osmotic solution concentration increases, increases the 1/ K 1 and therefore the initial mass transfer rate. The effect of steam blanching on the previous response is also obvious (cf. to Table 2) increasing the 1/K 1 value by 63% in the 15 o Brix solution and by 75% in the 30 o Brix solution. The K 2 value is related to equilibrium mass transfer terms, e.g., the higher the 1/K 2 value, the higher the equilibrium moisture content. The previous trend agrees with the respective variation of moisture content during the osmotic dehydration seen in Figure 2.
The effective diffusivities of water loss and solid gain were estimated employing Fickian diffusion (Table  3). It is observed that diffusivity is increased as solute concentration increases from 15 o Brix to 30 o Brix as was expected. In the present study during the osmotic dehydration, the water diffusivities were ranged from 3.2 -5.57×10 -11 m 2 /s for water loss and 1.27-2.03×10 -11 m 2 /s for solid gain at 30 o Brix and 2.12-4.27×10 -11 m 2 /s for water loss and 0.91-1.98×10 -11 m 2 /s for solid gain at 15 o Brix. Comparison of water diffusivity values found in literature should be carried out with great caution. Different experimental methods and conditions, mathematical analysis (analytical approach, method of slopes, regular regime method, numerical solution of water transport equations) and applied boundary conditions as well as different varieties of different physiological state and anatomy (peel, mesocarp, endocarp), should be taken into account otherwise the drawn conclusions could be misleading (Xanthopoulos et al., 2012). Park et al. (2002) working with pear cubes (case of no peel) found that water diffusivity was 0.35-1.92×10 -9 m 2 /s for water loss and 0.20-3.60×10 -9 m 2 /s for solid gain at 40-60 o C. Lazarides et al. (1997) Panades et al. (2008) reported water diffusivity 0.69-1.47×10 −10 m 2 /s during osmotic dehydration of guava (case of no peel) in sucrose solution. Khoyi and Hesari (2007) reported diffusivity 1.06-4.06×10 −9 m 2 /s of water loss and 7.69-3.13×10 −9 m 2 /s for solid gain of apricot slices (case of no peel) in sucrose solution.

Ascorbic acid
The analysis of variance (Table 4) showed that only steam blanching (treatment) affected significantly the ascorbic acid concentration (P<0.05). The previous response is expected since ascorbic acid is thermal sensitive and highly unsaturated, making it susceptible to degradation due to oxidation and heat treatment. The ascorbic acid concentration in Table 5 is higher than the one reported from Beveridge et al. (2002) and Araya-Farias et al. (2011) for the Indian Summer cultivar which was 175 mg/100 g and 184 mg/100 g respectively. Zeb (2004) reported that the variation of ascorbic acid in sea buckthorn depends on whether is measured on the seeds (64.4-92.7 mg/100 g of seed), juice (216 mg/100 g of berries) or pulp upon juice and pulp removal (481 mg/100 g of berries). Variations among most nutrients within origin or between origins offer prospects for future study. The high variability in sea buckthorn composition found in literature depends on the variety, maturity and growing location (Beveridge et al., 1999). As it is seen in Table 5, the steam blanched samples exhibit a higher reduction of the initial ascorbic acid (control) compared to untreated samples. In particular, the steam blanched samples exhibited 52% and 71% reduction of the initial ascorbic acid at 15 o Brix and 30 o Brix stevia solutions respectively (Table 5). Santos and Silva (2008) reported increased ascorbic acid losses, even 50%, along with increased water losses for different osmotic solutions due to steam blanching application that caused cracks on the waxy layer of fruit epidermis. On the other hand, the untreated samples exhibited less ascorbic acid losses of 23% and 28% respectively in the stevia solutions of 30 o Brix and 15 o Brix. Santos and Silva (2008) attributed the increased retention of ascorbic acid in the final product, at the formation of a coherent layer of sugars on their epidermis acting as a barrier to water transport and ascorbic acid loss.
Upon osmotic dehydration, the samples were airdried; the steam blanched samples at the end of the air drying had higher ascorbic acid losses of 95% and 91% for the 15°Brix and 30°Brix osmotic solutions respectively, while the untreated samples exhibited ascorbic acid losses of 80% and 65% respectively. As was expected, osmotic dehydration and air-drying involve thermal treatments and as such, causes a significant reduction of the ascorbic acid since it is thermally sensitive making it susceptible to degradation due to oxidation and heat processing. The previous results are consistent with those of Santos and Silva (2008) and Araya-Farias et al. (2011) who reported that the preservation of the nutrients in the sea buckthorn, especially that of the ascorbic acid depends on the temperature-time integral as well as the final moisture content of the produce.

Total soluble solids and acidity
The analysis of variance (    total soluble solids were significantly affected by steam blanching (P<0.05). The four experimental series, regarding the total soluble solids, were differed significantly among them as well as with the control samples. It was observed that the total soluble solids increase during the osmotic dehydration was higher in steam blanched samples against those not to, compared to the control samples (Table 7). This response is expected since steam blanching disintegrates the waxy layer of fruits epidermis causing cracks, facilitating likewise the influx of the osmotic solution into the mesocarp. This observation is in line with Araya-Farias et al. (2011) findings according to whose, steam blanching increases drastically total soluble solids in osmotically dehydrated sea buckthorn. A difference in the total soluble solids upon air-drying completion was also observed, as air-drying of the steam blanched samples resulted in higher total soluble solids compared to samples that had not been steam blanched (Table 7).
In addition, it was observed that the dry matter increase (Table 7) during the osmotic dehydration (Equation 3) was significantly affected by the steam blanching application. In particular, the samples that had been steam blanched and then osmotic dehydrated in 30 o Brix solution, exhibited an increase of 84% in the dry matter while the samples that had not been steam blanched an increase of 53%. Similarly, the samples osmotically dehydrated in 15 o Brix solution exhibited 82% dry matter increase when steam blanching had been preceded, and only 39% when the samples had not steam blanched. The effect of stevia solutions was not so pronounced in the steam blanched samples as far as the total soluble solids and the dry matter concerns (Table 7) probably due to accumulation of solids on the external cellular layer that acts as a barrier against the uptake of solids as has been previously explained. Beveridge et al. (2002) reported that quantitatively the most important organic acid in sea buckthorn is malic acid, but smaller quantities of citric, tartaric, and succinic acid exists, contributing to total titratable acidity. The acid values reported in the literature, range 1.11-2.34 mg/100 g for malic acid and 0.042-0.234 mg/100 g for citric acid depending on the variety, maturity and growing location (Beveridge et al., 1999). In the present study, the tested variety of sea buckthorn exhibited higher citric acid concentration as can be seen in Table 8. The analysis of variance (Table 6) showed that the acidity regarding the citric and malic acids was significantly affected by the interaction of steam blanching with the stevia solution concentration (P<0.05). From  citric acid concentrations tend to decrease during the osmotic dehydration and the following air-drying, reaching in some cases even 60-70% reduction compared to control samples.

Drying kinetics during hot-air drying
The initial moisture content of the samples subjected to osmotic dehydration and air-drying, was ranged between 1.93-2.28 kg w /kg dm in the case of 30 o Brix (steam blanched) and 2.28-2.88 kg w /kg dm in the case of 15 ο Brix (steam blanched). Respectively, the initial moisture content of the untreated samples was ranged between 1.73-2.42 kg w /kg dm in the case of 30 o Brix and 2.28-2.50 kg w /kg dm in the case of 15 ο Brix. In Figure 3 are seen the experimental drying curves of sea buckthorn at 50 o C along with the predicted moisture content curves by the Logarithmic model (Table 1). The moisture content decreases exponentially with drying time and thus, drying appears to take place at the falling rate period. The coefficients of Logarithmic model calculated from the non-linear regression are presented in Table 9. As can be seen, the Logarithmic model describes efficiently the experimental drying curves based on the statistical estimates R 2 adj >99% and SEE≤0.025. In Figure 3 is observed that the steam blanched samples in both osmotic solutions were dried faster, approximately 4-5 hours shorter than the untreated samples (16-17 hrs), a fact that comes as a consequence of weakening of the waxy layer lying on fruit's peel due to steam blanching. Figure 4 presents the water diffusivity against the moisture content for all the experimental series during the air-drying. It is noted that the water diffusivity of the steam blanched samples lie above the untreated ones and in particular the water diffusivity of steam blanched samples range between 2.11-2.29×10 -11 m 2 /s while those of untreated samples between 1.56-1.66×10 -11 m 2 /s. Kyriakopoulou et al. (2013) attributed this response to thermal pre-treatment that reduced the resistance of water diffusion through product's epidermis, in the present case, reducing the waxy layer lies on sea buckthorn epidermis. Since estimation of the water diffusivity was carried out at the same drying temperature (50 o C), its apparent sharp rise as the moisture ratio decreases in the drying curves, is driven solely by the moisture content. Saravacos and Maroulis (2001) reported that water diffusivity increases as moisture content decreases in porous foods due to porosity formation, which facilitates water transport within the drying product. At very low moisture contents (MR<0.1) the strongly bound water in food matrix forces water diffusivity to be reduced sharply.

Conclusion
Solution concentration and steam blanching pretreatment had a significant effect on the solid gain and water loss during the osmotic dehydration of sea buckthorn while both increased with increasing solution concentration but not to the same extent. In particular, solid gain was seven times lesser compared to water loss   Table 1). Data points are the means of three replicates. fact that was attributed to the high molecular weight of steviol glycoside which favours water loss at the expense of solid gain. Peleg model described efficiently the mass transfer kinetics at the studied experimental cases based on the statistical estimates R 2 adj >99% and SEE≤0.18. Steam blanching caused significant reduction of the ascorbic acid concentration and facilitated the total soluble solids and dry matter gain, reaching up to 84%. The Logarithmic model found to describe efficiently the experimental drying curves based on the statistical estimates R 2 adj >99% and SEE≤0.025. The water diffusivity in steam blanched samples was higher than in the untreated ones and in particular the water diffusivity of steam blanched samples ranged between 2.11-2.29×10 -11 m 2 /s while those of untreated samples between 1.56-1.66×10 -11 m 2 /s.