Influence of the osmotic agent on the osmotic dehydration of papaya (Carica papaya L.)

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1 Journal of Food Engineering 75 (2006) Influence of the osmotic agent on the osmotic dehydration of papaya (Carica papaya L.) Ânoar Abbas El-Aouar a, *, Patrícia Moreira Azoubel b, José Lucena Barbosa Jr. a, Fernanda Elizabeth Xidieh Murr a a Department of Food Engineering, College of Food Engineering, State University of Campinas, P.O. Box 6121, ZIP , Campinas, SP, Brazil b EMBRAPA Semi-Arid, BR 428, km 152, P.O. Box 23, Petrolina, PE, Brazil Received 23 June 2004; accepted 18 April 2005 Available online 29 June 2005 Abstract The objective of the present work was to study the influence of two different osmotic agents (sucrose and corn syrup) on the osmotic dehydration of papaya slices (Carica papaya L.). The study was carried out using two factorial experimental designs, with three independent variables whose levels varied from 44% to 56% w/w for concentration, from 34 to 46 C for temperature and from 120 to 210 min for immersion time. The responses of the experimental designs were the weight reduction (WR), water loss (WL), solids gain (SG) and water activity (a w ). The results showed that, considering the same osmotic pressure for both osmotic agents, the values obtained for WR, WL and SG for dehydration in sucrose solutions were higher than those obtained in corn syrup solutions, due to their high viscosity and polysaccharide content. The opposite behavior was observed for a w. The models obtained for the response variables followed a linear behavior except for SG. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Osmotic dehydration; Experimental design; Papaya 1. Introduction Osmotic dehydration is widely used for the partial removal of water from plant tissues by immersion in a hypertonic (osmotic) solution. The driving force for the diffusion of water from the tissue into the solution is provided by the higher osmotic pressure of the hypertonic solution. The diffusion of water is accompanied by the simultaneous counter diffusion of solutes from the osmotic solution into the tissue. Since the membrane responsible for osmotic transport is not perfectly selective, other solutes present in the cells can also be leached * Corresponding author. Tel.: ; fax: address: anoar@fea.unicamp.br (Â.A. El-Aouar). into the osmotic solution (Rastogi & Raghavarao, 2004; Sablani, Rahman, & Al-Sadeiri, 2002). The rate of diffusion of water from any material made up of such tissues depends upon factors such as: temperature and concentration of the osmotic solution, the size and geometry of the material, the solution-to-material mass ratio and the level of agitation of the solution. A number of recent publications have described the influence of these variables on mass transfer rates during osmotic dehydration (Corzo & Gomez, 2004; Rastogi & Niranjan, 1998; Rastogi, Raghavarao, & Niranjan, 1997). The use of the osmotic dehydration process in the food industry has several advantages: quality improvement in terms of color, flavor and texture, energy efficiency, packaging and distribution cost reduction, no chemical pretreatment, providing required product /$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi: /j.jfoodeng

2 268 Â.A. El-Aouar et al. / Journal of Food Engineering 75 (2006) stability and retention of nutrients during storage (Rahman & Perera, 1999; Sablani et al., 2002). The response surface methodology has been widely and effectively used in industrial investigations and other processes such as the development and/or improvement of the nutritional products, due to its practical utility in their optimization (Azoubel & Murr, 2003; Corzo & Gomez, 2004). This methodology presupposes the use of experimental design techniques to investigate and learn about the functional form of the process or system that involves one or more response variables that are influenced by various factors or independent variables. Therefore, our general objective was to study the influence of two different osmotic agents (sucrose and corn syrup) on the osmotic dehydration of papaya Formosa slices (Carica papaya L.). The specific objective was to model the influence of the concentration and temperature of the osmotic solution and the immersion time on changes in weight reduction, water loss, solids gain and water activity for both osmotic agents. 2. Material and methods 2.1. Raw material Papayas (Formosa variety) with similar maturity (10 12 Brix) and weight ( kg) were purchased in a local market. The samples were hand-peeled and cut into slices ( mm) using a cutter designed for this purpose Osmotic dehydration Papaya slices, previously weighed and identified, were immersed in the osmotic solutions (commercial sucrose and solid corn syrup from corn syrup solid MOR- REX Ò 1940 from Corn Products, Brazil) of given concentration (44 56% w/w) and temperature (34 46 C) during a given immersion time ( min). The studied range of immersion time was defined by a previous kinetics in the central point of concentration and temperature (50% w/w and 40 C) for a period of 8 h, for both osmotic agents. Therefore, identifying by the kinetic curves the region where there was no significant variation in the drying rates for both agents, it was possible to find the more appropriate range of immersion time to this study. A fruit:solution ratio of 1:10 was used. The osmotic process was carried out in a shaker (TEC- NAL TE-421) at a constant agitation of 80 rpm. After removing from the solution, the dehydrated slices of each group were drained and blotted with absorbent paper to remove the excess solution. The moisture content of the samples was gravimetrically measured using a vacuum oven (635 mmhg) at 60 C for 24 h. The weight and moisture content data of each sample were utilized in order to calculate the response variables weight reduction (WR), water loss (WL) and solids gain (SG), according to the following equations: WR ð%þ ¼ ðw i w f Þ 100 ð1þ w i WL ð%þ ¼ ðw ix i w f X f Þ 100 ð2þ w i SG ð%þ ¼ w f 1 X f 100 wi 1 X i ð3þ w i where w i and w f are the initial and final (time t) samples weights, respectively, (g); X i and X f are the initial and final (time t) samples moisture content, respectively, (g water/100 g initial wet papaya). Solutions and samples water activity (a w ) were measured with a water activity meter (AquaLab Series 3 TE) at 25 C with an accuracy of ± Experimental design and statistical analysis According to Table 1, two factorial experimental designs were used with three independent variables whose levels varied from 44% to 56% w/w for syrup concentration, from 34 to 46 C for temperature and from 120 to 210 min for immersion time, which required 11 experiments, including the center point. The responses of both designs were weight reduction, water loss, solids gain and water activity. Each experimental run was performed in triplicate. It was assumed that a mathematical function u exists for the response variable Y (WR, WL, SG and a w )in terms of three independent process variables (Khuri & Cornell, 1996), temperature, concentration and time: Y ¼ uðt ; C; tþ ¼b 0 þ b 1 T þ b 2 C þ b 3 t þ b 12 T C þ b 13 T t þ b 23 C t ð4þ where b is the equation coefficient and the subscripts 0, 1, 2, 3, 12, 13 and 23 correspond to the mean value of the function u, temperature, concentration, immersion time, interaction between temperature and concentration, interaction between temperature and immersion time and interaction between concentration and immersion time, respectively. In order to obtain the regression coefficients an analysis of variance (ANOVA) using the Statistica 5.0 (Statsoft, 1997) package was performed. 3. Results and discussion 3.1. Fitting models Regression coefficients for the coded first-order polynomial equations are displayed in Table 2. The resulting

3 Â.A. El-Aouar et al. / Journal of Food Engineering 75 (2006) Table 1 Experimental data for weight reduction, water loss, solids gain and water activity under different treatment conditions of solution temperature and concentration and immersion time Treatment Sucrose Corn syrup T ( C) C a (% w/w) t (min) WR (%) WL (%) SG (%) a w WR (%) WL (%) SG (%) a w 34( 1) 44( 1) 120( 1) ( 1) 56(+1) 120( 1) ( 1) 44( 1) 210(+1) ( 1) 56(+1) 210(+1) (+1) 44( 1) 120( 1) (+1) 56(+1) 120( 1) (+1) 44( 1) 210(+1) (+1) 56(+1) 210(+1) (0) 50(0) 165(0) (0) 50(0) 165(0) (0) 50(0) 165(0) a Water activity of sucrose solutions at 25 C: (44% w/w); (50% w/w); (56% w/w). Water activity of corn syrup solutions at 25 C: (44% w/w); (50% w/w); (56% w/w). Table 2 Values of coded first-order polynomial regression coefficients Coefficients Sucrose Corn syrup WR WL SG a w WR WL SG a w b b ns ns b b b ns b ns ns b ns ns ns: non-significant (p > 0.05). equations for both experimental designs were tested for adequacy and fitness by analysis of variance (ANOVA) according to Tables 3 and 4. To convert the real values that include the studied range of the independent variables in coded ones, according to Eq. (4), the following equation can be used: RV CP CV ¼ ð5þ DRV CP where CV is the coded value; RV is the real value; CP is the real central point value; DRV CP is the step change at the central point. Tables 3 and 4 summarize the results for linear and cross-product terms for weight reduction, water loss, solids gain and water activity for each solute; some non-significant terms (p > 0.05) were eliminated, in agreement with Table 2. According to Table 3, the fitted models were significant (p ), possessing low residual values and satisfactory values of multiple determination coefficients. By Table 4, only the model for the solids gain was not predictive, presenting significant lack of fit, therefore, the curves generated from this model can only show the behavior of each independent variable on the responses. It is important to point out that, for the analysis of variance shown in Tables 3 and 4, the largest contribution in the residual value was due to the lack of fit, indicating that the experimental data presented good reliability Influence of process variables Figs. 1 and 2 show the influence of concentration and temperature of the osmotic solution and immersion time on the weight loss, loss of water, solids gain and water activity during the osmotic dehydration of papaya in sucrose and corn syrup, respectively. According to Figs. 1(a) and (b), the osmotic solution concentration was the most important effect on weight reduction and water loss, followed by the immersion time, and they positively affected these responses for the sucrose agent. The effect of temperature of the osmotic solution practically did not influence the weight reduction and it was negative. The weight reduction exhibits a mass relationship among the whole flows involved in the osmotic process (mainly between water loss and solids gain) and due to this which is more pronounced in the solids gain instead of the the water loss,

4 270 Â.A. El-Aouar et al. / Journal of Food Engineering 75 (2006) Table 3 Analysis of variance for weight reduction (WR), water loss (WL), solids gain (SG) and water activity (a w ) in the osmotic dehydration of papaya in sucrose solutions Source SS DF MS F c F t Weight reduction (WR) Regression Residual Lack of fit Pure error Total R 2 = Water loss (WL) Regression Residual Lack of fit Pure error Total R 2 = Solids gain (SG) Regression Residual Lack of fit Pure error Total R 2 = Water activity (a w ) Regression 8.6E E Residual 1.4E E-06 Lack of fit 1.3E-05 4 Pure error 6.7E-07 2 Total 8.8E R 2 = SS: sum square; DF: degree of freedom; MS: mean square; F c : calculated F distribution value (p ); F t : tabulated F distribution value (p ). the negative effect of temperature found on weight reduction could be explained. The temperature did not significantly influence the water loss. Values of 40% for WR and of 52% for WL can be obtained when the concentration and the immersion time are in their highest levels, considering the whole temperature range, practically. Observing Fig. 1(c), for sucrose, the temperature was the most important effect affecting solids gain, followed by the immersion time. These effects positively influenced the solids gain for the osmotic process of papaya in sucrose solutions. It is important to emphasize the negative effect of the concentration in solids gain for sucrose. According to Heng, Guilbert, and Cuq (1990), it should be mentioned that, in this case, the sugar gain is less important. Generally speaking it appears that little sugar is obtained when the water outflow is fast and significant. This occurs with a higher temperature, higher concentration and some agitation. Acceleration of water loss without modification of solids gain, when temperature or dehydration solution concentration is increased, is observed by many authors (Bongirwar & Sreenivasan, 1977; Hawkes & Flink, 1978; Islam & Flink, 1982). This effect is generally attributed to the influence of natural tissue membranes as well as to the diffuse properties of water and solutes as a function of their respective molar mass. Low values of solids gain (<10%) can be obtained using temperature of the osmotic solution and immersion time in their lowest levels, with the concentration in its highest level. Fig. 1(d) shows that the immersion time was the most important effect on water activity, followed by concentration and temperature. All the effects were negative on water activity for sucrose solutions. Values of a w inferior to can be obtained using the independent variables in their highest levels. In agreement with Fig. 2(a) and (b), the osmotic solution concentration was the most important effect on weight reduction and water loss, followed by the immersion time and temperature of osmotic solution, and they positively affected these responses for corn syrup. Values of 27% for WR and of 35% for WL can be obtained when the independent variables are in their highest levels. Considering the corn syrup agent, the temperature did not influence the solids gain but it was positively and strongly affected by the immersion time and with less intensity by the solution concentration (Fig. 2(c)). Fig. 2(d) shows that the immersion time and the temperature of the osmotic solution were the most important effects on water activity. All the effects were negative on water activity for corn syrup solutions. Values of a w, inferior to can be obtained using the independent variables in their highest levels.

5 Â.A. El-Aouar et al. / Journal of Food Engineering 75 (2006) Table 4 Analysis of variance for weight reduction (WR), water loss (WL), solids gain (SG) and water activity (a w ) in the osmotic dehydration of papaya in corn syrup solutions Source SS DF MS F c F t Weight reduction (WR) Regression Residual Lack of fit Pure error Total R 2 = Water loss (WL) Regression Residual Lack of fit Pure error Total R 2 = Solids gain (SG) Regression Residual Lack of fit Pure error Total R 2 = Water activity (a w ) Regression 9.3E E Residual 2.2E E-07 Lack of fit 1.9E-06 4 Pure error 2.2E-07 2 Total 9.5E R 2 = SS: sum square; DF: degree of freedom; MS: mean square; F c : F distribution calculated (p ); F t : F distribution tabulated (p ). In agreement with Table 1, for the same solute concentration, the osmotic potential of sucrose solutions is larger than corn syrup solutions. To compare between both osmotic agents it is necessary to use solutions with the same initial osmotic potential because water activity is the driving force of the osmotic process. According to Lewicki and Lenart (1995), excess pressure needed to reach the state of equilibrium between a pure solvent and a solution is called osmotic pressure. In the equilibrium state, Chemical potential solvent solvent ¼ Chemical potential P solution 1 solvent P 2 ð6þ Since in foods, water is the solvent, Eq. (7) can be used: P ¼ T lnða w Þ ð7þ where P is the osmotic pressure (Pa); a w is water activity and T is the absolute temperature (K). Fig. 3 illustrates the higher osmotic pressure of sucrose solutions compared to corn syrup ones, in terms of the concentration of osmotic solution, using the water activity data from Table 1. Observing Fig. 3, it is possible to obtain a relationship between both curves considering the same osmotic potential. It results in the following equation: C Sucrose ¼ 0.83C 1.01 Corn syrup ð8þ where C corresponds to the real value of osmotic solution concentration. Obeying the established relationship in Eq. (8), it is possible to obtain the pairs of solution concentrations for both osmotic agents corresponding to the same osmotic pressure. Taking into account Eq. (8) and according to Figs. 1(a) and 2(a) for an osmotic solution temperature of 34 C and an immersion time of 120 min, the difference between the weight reduction values of both osmotic agents, for the same osmotic pressure, indicates that samples dehydrated in corn syrup solutions had approximately a weight reduction 30% less than samples processed in sucrose solutions. Considering an osmotic solution temperature of 46 C and an immersion time of 210 min, samples dehydrated in sucrose solutions had approximately a weight reduction 20% less than samples processed in corn syrup solutions due to the small effect of temperature in this response variable using sucrose solutions. Figs. 1(b) and 2(b) show that the differences between the water loss value of both osmotic agents, for the same temperature, immersion time and osmotic pressure, indicate that samples dehydrated in corn syrup solutions had approximately a water loss of 7 40% less than samples processed in sucrose solutions.

6 272 Â.A. El-Aouar et al. / Journal of Food Engineering 75 (2006) Fig. 1. Influence of concentration and temperature of osmotic solution and immersion time on (a) WR, (b) WL, (c) SG and (d) a w for papaya osmotic dehydration with sucrose solutions. In agreement with Figs. 1(c) and 2(c), the differences between the solids gain value of both osmotic agents, for the same temperature, immersion time and osmotic pressure, indicate that samples dehydrated in corn syrup solutions had approximately a solids gain of 53 56% less than samples processed in sucrose solutions. According to Figs. 1(d) and 2(d), it was observed that samples dehydrated in sucrose solutions reached a water activity value of 1 3% less than samples processed in corn syrup solutions. On the whole, samples dehydrated in sucrose solutions had values of WR, WL and SG higher than those

7 Â.A. El-Aouar et al. / Journal of Food Engineering 75 (2006) Fig. 2. Influence of concentration and temperature of osmotic solution and immersion time on (a) WR, (b) WL, (c) SG and (d) a w for papaya osmotic dehydration with corn syrup solutions. obtained for samples processed in corn syrup solutions, except for a w, even when considering the same osmotic pressure for both osmotic agents. The fact is that the corn syrup solutions had visually a higher viscosity than the sucrose ones. The use of highly concentrated viscous sugar solutions creates major problems such as floating of food pieces, hindering the contact between the food material and the osmotic solution, causing a reduction in the mass transfer rates. Mavroudis, Gekas, and Sjöholm

8 274 Â.A. El-Aouar et al. / Journal of Food Engineering 75 (2006) Osmotic pressure (Pa) 1.2x10 7 Sucrose 1.1x10 7 Corn syrup 1.0x x x x x10 6 When water loss and solid gain take place in a parallel mode; the rate of water loss is always higher than the rate of solid gain. The solution concentration and temperature and immersion time have a significant effect on weight reduction, water loss, solids gain and water activity during the osmotic dehydration of papaya slices with sucrose and corn syrup. Considering the same osmotic pressure for both osmotic agents, it was found that weight reduction, water loss and solids gain were higher when sucrose was used as an osmotic agent, however, the osmotic dehydration in corn syrup solutions led to higher values of water activity. Acknowledgements The authors acknowledge CAPES (Coordination of Perfectioning Superior Level Staff) and Corn Products, Brazil. 5.0x x10 6 (1998) affirm that the increase of agitation level could be a good alternative for this case. In early works (Bongirwar & Sreenivasan, 1977; Ponting, Watters, Forrey, Jackson, & Stanley, 1966) the effect of agitation was studied by comparison of agitated and non-agitated treatments. Analysis of the agitation effect was limited to weight loss and was without quantification. However, it was clear that agitated samples exhibited greater weight reduction, and consequently water loss, than non-agitated ones and thus agitation was found to be another process parameter. Chemical and physical properties of corn syrup solids given by the Corn Products, Brazil, were as follows. Moisture content max. 5.0%; dextrose equivalent 38 40; ph ; carbohydrates (% dry basis): dextrose 15, maltose 12, other sugars 73. According to Lazarides, Katsanidis, and Nickolaidis (1995), overall mass transfer coefficients for sugar uptake decrease with the molecular size of the osmotic solute. The larger the solute size, the lower the sugar uptake under fixed process conditions. 4. Conclusions Concentration (% w/w) Fig. 3. Relationship between concentration and osmotic pressure of sucrose and corn syrup osmotic solutions. References Azoubel, P. M., & Murr, F. E. X. (2003). Optimization of osmotic dehydration of cashew apple (Anacardium occidentale L.) in sugar solutions. Food and Science Technology International, 9, Bongirwar, D. R., & Sreenivasan, A. (1977). Studies on osmotic dehydration of banana. Journal of Food Science and Technology, 14, Corzo, O., & Gomez, E. R. (2004). Optimization of osmotic dehydration of cantaloupe using desired function methodology. Journal of Food Engineering, 64, Hawkes, J., & Flink, J. M. (1978). Osmotic concentration of fruits slices prior to freeze dehydration. Journal of Food Processing Preservation, 2, Heng, K., Guilbert, S., & Cuq, J. L. (1990). Osmotic dehydration of papaya: Influence of process variables on the product quality. Sciences des Aliments, 10, Islam, M. N., & Flink, J. M. (1982). Dehydration of potato. II. Osmotic concentration and its effects on air drying behaviour. Journal of Food Technology, 17, Khuri, A. J., & Cornell, F. A. (1996). Response surfaces: Design and analyses. New York: Marcel Dekker, 510p. Lazarides, H. N., Katsanidis, E., & Nickolaidis, A. (1995). Mass transfer kinetics during osmoticpreconcentration aiming at minimal solid uptake. Journal of Food Engineering, 25, Lewicki, P. P., & Lenart, A. (1995). Osmotic dehydration of fruits and vegetables. In A. S. Mujumdar (Ed.), Handbook of industrial drying (pp ). New York: Marcel Dekker. Mavroudis, N. E., Gekas, V., & Sjöholm, I. (1998). Osmotic dehydration of apples effects of agitation and raw material characteristics. Journal of Food Engineering, 35, Ponting, J. D., Watters, G. G., Forrey, R. R., Jackson, R., & Stanley, W. L. (1966). Osmotic dehydration of fruits. Food Technology, 20, Rahman, M. S., & Perera, C. O. (1999). Drying and food preservation. In M. S. Rahman (Ed.), Handbook of food preservation (pp ). New York: Marcel Dekker. Rastogi, N. K., & Niranjan, K. (1998). Enhanced mass transfer during osmotic dehydration of high pressure treated pineapple. Journal of Food Science, 63, Rastogi, N. K., & Raghavarao, K. S. M. S. (2004). Mass transfer during osmotic dehydration of pineapple: Considering Fickian diffusion in cubical configuration. Lebensmittel-Wissenschaft und- Technologie, 37, Rastogi, N. K., Raghavarao, K. S., & Niranjan, K. (1997). Mass transfer during osmotic dehydration of banana: Fickian diffusion in cylindrical configuration. Journal of Food Engineering, 31, Sablani, S. S., Rahman, M. S., & Al-Sadeiri, D. S. (2002). Equilibrium distribution data for osmotic drying of apple cubes in sugar-water solution. Journal of Food Engineering, 52, Statsoft (1997). Statistica for windows. Tulsa. USA.