APPLICATION OF PELEG MODEL TO STUDY MASS TRANSFER DURING OSMOTIC DEHYDRATION OF APPLE IN SUGAR BEET MOLASSES

Transcription

1 APPLICATION OF PELEG MODEL TO STUDY MASS TRANSFER DURING OSMOTIC DEHYDRATION OF APPLE IN SUGAR BEET MOLASSES Nevena M. Mišljenović a *, Gordana B. Koprivica a, Lato L. Pezo b, Tatjana A. Kuljanin a, Marija I. Bodroţa Solarov c and Bojana V. Filipĉev c a University of Novi Sad, Faculty of Technology, Bulevar cara Lazara 1, Novi Sad, Serbia b University of Belgrade, Instutute of General and Physical Chemistry, Studentski trg 12-16, Belgrade, Serbia с University of Novi Sad, Institute for Food Technology, Bulevar cara Lazara 1, Novi Sad, Serbia The applicability of Peleg equation was examined for the description of mass transfer during osmotic dehydration (OD) of apple in sugar beet molasses. Mass transfer was investigated in terms of water loss (WL) and solid gain (), during OD in 40-80% sugar beet molasses solutions, at 45, 55 and 65ºC. High regression coefficients obtained for Peleg constants (R 2 >0.975) indicate good fit to the experimental data. The Peleg rate constant varied from to (g/g i.s.w.) and from to (g/g i.s.w.) for WL and, respectively. The Peleg capacity constant varied from to (h g/g i.s.w.) and from to (h g/g i.s.w.) for WL and, respectively. The equilibrium WL and were estimated using the Peleg model. In addition, the activation energy (E a ) for WL and was determined from the relationship between the Peleg rate constant and Arrhenius equation. KEY WORDS: Peleg model, osmotic dehydration, sugar beet molasses INTRODUCTION The development of new, high-quality and consumer-attractive dried products is necessary to widen product availability and diversify the markets, since fresh crops consumption is generally below the levels recommended in a normal diet (1). Conventional air-drying is the most frequently used dehydration operation in the food and chemical industry, but a lot of research work is oriented to find new drying methods which are less energy intensive and nutritive favorable. OD is a water removal process, which is based on soaking foods (fruit, vegetable, meat and fish) in a hypertonic solution. Water removal in liquid form, usage of mild temperatures and osmotic solution reusing are main advantages of OD in comparison with other drying treatments (2, 3, 4). The driving force for the OD process is the difference in * Corresponding author: Nevena M. Mišljenoviš, University of Novi Sad, Faculty of Technology, Bulevar cara Lazara 1, Novi Sad, Serbia, nevenam@uns.ac.rs 91

2 osmotic pressure between the food material (hypotonic medium) and osmotic solution (hypertonic medium). The diffusion of water is accompanied by the simultaneous counter-diffusion of solute from the osmotic solution to the tissue (5, 6). The rate of diffusion of water from the fruit tissue depends upon factors such as the temperature and concentration of osmotic solution, size and geometry of the material, the solution to material ratio, level of agitation of the solution and the type of apparatus (7, 8). Тhe most commonly used osmotic agents are sucrose and sodium chloride and their combination. Research has shown that the use of sugar beet molasses as hypertonic solution improves OD processes (9, 4). Sugar beet molasses is an appropriate medium for OD, primarily due to the high dry matter (above 80%). Different approaches have been proposed to explain the rates of mass transfer during OD (10, 11, 12). However, it is very difficult to develop a mathematical model capable to incorporate all of the factors involved in the process. Rastogi, Raghavarao, Niranjan and Knorr (13) reported Fickian unsteady-state diffusion as the most appropriate mechanism for the estimation of diffusion coefficients during the osmotic concentration. The major drawback in the application of this law is the long experimental time required to attain equilibrium WL. Much work has been done in developing models to predict the mass transfer kinetics of OD and some empirical and semi-empirical models have been proposed. These models correlate the processing variables with WL or without taking into account the underlying phenomena of simultaneous water and soluble transfer process, but they include fitting of the proposed function to experimental data, multi-variable regressions, response surface analysis, models derived from mass balances, etc (11). Even though the empirical and semi-empirical models that have been proposed in the literature give a reasonable fit to experimental data, their use is limited because they are only capable of representing data under conditions similar to those for which such models were developed, and they cannot take into account the process complexity (14). Peleg (14) proposed a two-parameter sorption equation and tested its prediction accuracy during water adsorption of milk powder and whole rice, and soaking of whole rice. Palou, Lopez-Malo, Argaiz, and Welti (16) studied simultaneous water desorption and sucrose absorption during OD of papaya using Peleg model. In the literature, there is a lack of information about using Peleg model for the OD in sugar beet molasses solutions. The objectives of this study were: (1) the determination of the applicability of Peleg equation in modeling the mass transfer during OD of apple in sugar beet molasses; and (2) the determination of equilibrium water and solid contents for OD at different concentrations and temperatures. EXPERIMENTAL Material Apple samples were purchased in a local market in Novi Sad (Serbia) and stored at 4ºC until the use. Initial moisture content, X wo, was ± 1.49 %. 92

3 Sugar beet molasses was obtained from the sugar factory Pešinci, Serbia. Initial dry matter content in the molasses was 83.68%. For dilution of sugar beet molasses, distilled water was used. Osmotic dehydration The apple samples were washed thoroughly and peeled manually (using a stainless kitchen peeler). The peeled apples were manually sliced into cubes, dimension 1x1x1 cm using a kitchen slicer. Dimensions of the cubes were checked with caliper. An amount of 100 g of sliced apple cubes samples were prepared for each treatment. Different concentrations of sugar beet molasses (40.0%, 60.0% and 80.0% dry matter) were used as osmotic solution. The effect of temperature was also investigated and the experiments were conducted at 45, 55 and 65ºC. The apple cubes were put in the glass jars with 1000 g of molasses solution with a material/solution ratio of 1:10 (w/w). The jars were placed in the heat chamber and the process proceeded without agitation. After each sampling time (5, 10, 15, 20, 30, 45, 60, 90, 120, 180, 240, 300 minutes), the cubes were taken out, washed with water and gently blotted with filter paper in order to remove the excessive water and weighed. Dry matter content of the fresh and treated samples was determined by drying the material at 105 ºC for 24h in a heat chamber (Instrumentaria Sutjeska, Serbia). Soluble solids content of the molasses solutions was measured at 20 ºC using an Abbe refractometer, Carl Zeis Jenna. Evaluation of mass exchange between the solution and the sample during OD were made by using the parameters such as WL and. In order to account for the initial weight differences between the samples, the WL and were calculated according to the following equations: where m i and m f are the initial and final weight (g) of the samples, respectively; z i and z f are the initial and final mass fraction of water (g water/g sample), respectively; s i and s f are the initial and final mass fraction of total solids (g total solids/g sample), respectively; i.s.w. means initial sample weight. The equation proposed by Peleg (15) is: Peleg model where X w is the moisture content expressed on dry basis at time t; X wo is the initial moisture content expressed on dry basis; k 1 (h g/g) is the Peleg rate constant, and k 2 (g/g) is the Peleg capacity constant. In this paper, in the Peleg equation, instead of the moisture content is included WL or. In the next equations, Y represents WL or. [4] where k 1 Y and k 2 Y are the Peleg constants for WL or. [1] [2] [3] 93

4 The Peleg rate constant k 1 relates to the dehydration rate at the very beginning, t = t 0. [5] The Peleg capacity constant k 2 relates to the minimum attainable moisture content. As t, equation [4] gives the relation between equilibrium WL or and k 2. At the equilibrium, Peleg s equation for WL and is: [6] The linearization of equation [4] gives: [7] The plot of equation [4] is a straight line, where k 1 is the intercept and k 2 is the slope. The major advantage of the Peleg model is to save time by predicting water sorption kinetics of foods, including the equilibrium moisture content using short-time experimental data. Statistical analysis Descriptive statistical analyses for calculating the means and the standard error of the mean were performed using MicroSoft Excel software (MicroSoft Office 2003). All obtained results were expressed as the mean ± standard deviation (SD). The one-way ANOVA of obtained results were accomplished using StatSoft Statistica ver Statistical evaluation of the results was performed using 3x3x13 factorial design (three concentrations, three temperatures and thirteen time intervals). Analyisis of variance (ANOVA) was carried out to examine the effects (p<0.05) of temperature and concentration on Peleg constants. RESULTS AND DISCUSSION Water loss and solid gain Figure 1 show the experimental data for WL and during OD of apple at different concentration of sugar beet molasses and operating temperature. The nonlinear increase of WL and was observed at all concentrations and temperatures during the process. Increasing of concentration had a positive influence on dehydration effectiveness, i.e. WL increased while decreased. If we observe WL and in relation to the time of immersion, an initial high rate of water removal (and solid uptake) followed by slower removal (and uptake) in the later stages was observed. Rapid loss of water (and solid uptake) in the beginning is apparently due to the large osmotic driving force between the fresh apple cubes and the surrounding hypertonic medium (sugar beet molasses) and indicates that the system is getting closer to the end of the osmotic process (pseudo-equilibrium) (17). The highest WL (0.836 g/g of i. s. w.) was observed in the sample which was dehydrated in the molasses with 80% solid content at 65ºC for 5 hours. 94

5 Solid gain (g/g i.s.w.) Water loss (g/g i.s.w.) APTEFF, 42, (2011) UDC: :[ : Time (h) Time (h) Figure 1. Plot of WL and during OD of apple in sugar beet molasses at different concentration and temperature ( 80%, 45ºC, - 60%, 45ºC, - 40%, 45ºC, - 80%, 55ºC, - 60%, 55ºC, - 40%, 55ºC, - 80%, 65ºC, - 60%, 65ºC, - 40%, 65ºC) The value indicates the degree of penetration of solids from the osmotic solution into the samples. Many other authors showed that a higher solution concentration caused a higher solids uptake (17-20), but in those studies simple osmotic solutions were used (pure sucrose or salt solutions). The results of this study implicate that, in the case when sugar beet molasses is used as hypertonic solution, the increase of concentration caused a decrease of the solute penetration into treated samples, mainly due to the high viscosity of the molasses. By using highly concentrated solutions, a considerable product weight loss can be achieved along with a low solute gain (21). Peleg constants Experimental data of WL and were used to evaluate the adequacy of the Peleg equation. The coefficient of determination values, R 2, varied from for both 95

6 WL and. Such high values of R 2 indicate a good fit to the experimental data and suggest that the Peleg equation describes adequately the mass transfer kinetics terms during the osmotic dehydration of apple in sugar beet molasses. Table 1. Peleg rate (k 1 ) and capacity (k 2 ) constants and goodness of fit of Peleg model under different conditions of molasses concentration and temperature (all k 1 WL, k 1, k 2 WL, k 2 and R 2 values are significant at the 0.05 level) Temp. ( o C) Conc. Water loss Solid gain (%) WL k 1 WL k 2 R 2 k 1 K 2 R ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± The k 1 and k 2 values for different solution concentrations and temperatures are shown in Table 1. The reciprocal of k 1 describes the initial mass transfer rate, i.e. the lower the k 1, the higher mass transfer rate. It can be seen from the data in Table 1 that at a constant temperature k 1 WL decrease with increasing of concentration, while k 1 increases with concentration. This was expected if we take into account the influence of concentration on WL and (shown in Figure 1). Both k 1 WL and k 1 decrease with increasing temperature. The presented findings are similar to those reported by Corozo and Bracho (22) and Ganjloo et al. (23). Table 1 also shows the values of Peleg capacity constants for WL and. The capacity constants are related to equilibrium WL and, i.e. the lower the k 2 higher equilibrium WL or. The k 2 WL decreases with increasing concentration, k 2 increases with concentration, while both k 2 WL and k 2 decrease with increasing temperature. Multiple linear regression of the fitted data for the Peleg rate and capacity constants for water loss and solid gain can be derived as a function of temperature (T) and molasses concentration (C), from the data presented in Table 1. The fitted models correspond to data presented in Table 2. Table 2. Linear regression coefficients for Pelag coefficients (all values are significant at 0.05 level, 95% confidence limit) Peleg coefficient Intercept Temperature term Concentration term R 2 WL k ± ± ± k ± ± ± WL k ± ± ± ± ± ± k 2 96

7 The equilibrium values of WL and (Table 3) were estimated using Eq. [6]. The equilibrium point is reached when the water activities of apple and solution become equal. Both WL and influence the decrease in the water activity, which means that the relationship between these two phenomena influences the attainment of the equilibrium point (22). Table 3. WL and at equilibrium under different conditions of molasses concentration and temperature (all WL and values are significant at the 0.05 level) Temperature (ºC) Concentration (%) WL The linearized Arrehnius equation [8] shows the temperature dependency of the Peleg rate constant (k 1 ): (8) where k 1 is the Peleg rate constant for WL or (h g/g); k 0 is the frequency factor (1/h); E a is the activation energy (kj/mol); R the universal gas constant (8.314 J/mol K), and T is the absolute temperature (K). The plot of the logarithm of the Peleg rate constant vs. 1/T would gives a straight line with the negative slope equal E a / R and the intercept ln k 0. The linearity of the data (R 2 >0.892) reveals that the Peleg rate constant for WL and followed an Arrhenius equation as a function of temperature, regardless of the concentration. The values of E a and lnk 0 are presented in Table 4. Higher E a indicates the greater temperature sensitivity of k 1 constant. Table 4. Parameters of Arrhenius equation for the Peleg rate constant of and WL at different sucrose concentrations (all E a and R 2 values are significant at 0.05 level) Parameter Concentration (%) Water loss ln k ± ± ±2.154 E a (KJ/mol) ± ± ±5.868 R Solid gain ln k ± ± ±0.588 E a (KJ/mol) 5.564± ± ±1.601 R

8 CONCLUSION The Peleg equation described adequately the water loss and solid gain behavior of apples during osmotic dehydration in sugar beet molasses in the studied range of solution concentration and temperature. Solution concentration and temperature had a significant effect on the Peleg constants at 0.05 level, 95% confidence limit. The Peleg rate constant for water loss and solid gain followed an Arrhenius relationship. Acknowledgement The authors acknowledge financial support of the Ministry of Education and Science of the Republic of Serbia, III , REFERENCES 1. Contreras, C., Martin-Esparza, M.E., Chiralt, A. and Martinez, N.N.: Influence of microwave application on convective drying: Effects on drying kinetics, and optical and mechanical properties of apple and strawberry. J. Food Eng. 88 (2008) Della Rosa, M. and Giroux F.: Osmotic treatments (OT) and problems related to the solution management. J Food Eng. 49 (2001) Torreggiani D.: Osmotic dehydration in fruit and vegetable processing. Food Res. Int. 26 (1993) Koprivica, G., Mišljenoviš, N., Leviš, Lj. and Pribiš, V.: Changes in nutritive and textural quality off apple osmodehydrated in sugar beet molasses and saccharose solutions. APTEFF 40 (2009) Rastogi, N.K. and Raghavarao, K.S.M.S.: Mass transfer during osmotic dehydration: Determination of moisture and solute diffusion coefficients from concentration profiles. Food Bioprod. Process. 82, C1 (2004) Lazarides, H. N.: Reasons and possibilities to control solids uptake during osmotic treatment of fruits and vegetables, in Osmotic Dehydration and Vacuum Impregnation. Eds. Fito, P., Chiralt, A., Barat, J. M., Spiess, W. E. L. and Behsnilian, D., Technomic Publishing Company, inc., Lancaster (2001), Ch Ozen, B. F., Dock, L. L., Ozdemir, M. and Floros, J. D.: Processing factors affectting the osmotic dehydration of diced green peppers. Int. J. Food. Sci. Tech. 37 (2002) Uddin, M. B., Ainsworth, P. and İbanoğlu, Ş.: Evaluation of mass exchange during osmotic dehydration of carrots using response surface methodology. J. Food Eng. 65 (2004) Mišljenoviš, N., Koprivica, G., Leviš, Lj., Filipţev, B. and Kuljanin, T.: Osmotic dehydration of red cabbage in sugar beet molasses mass transfer kinetics. APTEFF 40 (2009) Marcotte, M., Toupin, C. J. and LeMaguer, M.: Mass transfer in cellular tissues. Part I: The mathematical model. J. Food Eng. 13 (1991)

9 11. Domeneghini Mercali, G., Ferreira Marczak, L. D., Tessaro, I. C., Zapata Norena, C. P.: Evaluation of water, sucrose and NaCl effective diffusivities during osmotic dehydration of banana (Musa sapientum, shum.). Food Sci. Technol - LEB 44 (2011) Hawkes, J. and Flink J. M.: Osmotic concentration of fruit slices prior to freeze dehydration. J. Food Process. Preserv. 2 (1978) Rastogi, N. K., Raghavarao, K. S. M. S., Niranjan, K., and Knorr, D.: Recent developments in osmotic dehydration: Methods to enhance mass transfer. Trends Food Sci. Tech. 13, 2 (2002) Ispir, A. and Togrul, I.: Osmotic dehydration of apricot: Kinetics and the effect of process parameters. Chem. Eng. Res. Des. 87 (2009) Peleg, M.: An empirical model for the description of moisture sorption curves. J. Food Sci. 53, 4 (1988) Palou, E., Lopez-Malo, A., Argaiz, A., and Welti, J.: Use of Pelegs equation to osmotic concentration of papaya. Dry. Technol. 12 (1994) Azoubel P. M. and Murr F. E. X.: Optimization of the osmotic dehydration of cashew apple (Anacardium occidentale L.) in sugar solutions. Food Sci. Technol. Int. 9 (2003) Lazarides, H. N., Katsanidis, E. and Nickolaidis, A.: Mass transfer kinetics during osmotic preconcentration aiming at minimal solid uptake. J. Food Eng, 25 (1995) Sereno, A.M., Moreira, R. and Martinez, E.: Mass transfer coefficients during osmotic dehydration of apple in single and combined aqueous solutions of sugar and salt. J. Food Eng. 47 (2001) Chenlo, F., Moreira, R., Fernandez-Herrer, C. and Vazquez, G.: Osmotic dehydration of chestnut with sucrose: Mass transfer processes and global kinetics modeling. J. Food Eng. 78 (2007) Ertekin, F. K., and Cakaloz, T.: Osmotic dehydration of peas: I. Influence of process variables on mass transfer. J. Food Process. Pres. 20 (1996) Corzo, O., and Bracho, N.: Application of Peleg s model to study mass transfer during osmotic dehydration of sardine sheets. J. Food Eng. 75 (2006) Ganjloo, A., Rahman, R. A., Bakar, J., Osman, A. and Bimakr, M.: Kinetics modeling of mass transfer using Peleg s equation during osmotic dehydration of seedless guava (Psidium guajava L.): Effect of process parameters. Food Bioprocess Technol. DOI /s

10 ПРИМЕНА ПЕЛЕГОВОГ МОДЕЛА У АНАЛИЗИ ПРЕНОСА МАСЕ ТОКОМ ОСМОТСКЕ ДЕХИДРАТАЦИЈЕ ЈАБУКЕ У МЕЛАСИ ШЕЋЕРНЕ РЕПЕ Невена М. Мишљеновић a, Гордана Б. Копривица a, Лато Л. Пезо б, Татјана А. Куљанин a, Мaрија И. Бодрожа Соларoв в и Бојана В. Филипчев в a Универзитет у Новом Саду, Технолошки факултет, Булевар цара Лазара 1, Нови Сад, Србија б Универзитет у Београду, Институт за општу и физичку хемију, Студентски трг 12-16, Београд, Србија в Универзитет у Новом Саду, Институт за прехрамбене технологије, Булевар цара Лазара 1, Нови Сад, Србија У раду је испитана могућност примене Пелеговог модела за описивање преноса масе током осмотске дехидратације јабуке у растворима меласе шећерне репе. Пренос масе је испитиван преко губитка воде (ВЛ) и прираштаја суве материје (СГ), током дехидратације у 40-80% растворима меласе шећерне репе, на температурама од 45, 55 и 65 ºC. Високе вредности регресионих коефицијената (R 2 >0,975) указују да Пелегова једначина адекватно описује експерименталне рeзултате. Пелегова константа брзине је варирала у опсегу од 0,144 до 0,785 (g/g п.у.) и од 2,006 до 4,436 (g/g п.у.) за ВЛ и СГ, респективно. Пелегова капацитативна константа је варирала у опсегу од 1,142 до 1,553 (h g/g п.у.) и од 8,254 до 11,930 (h g/g п.у.) за ВЛ и СГ, респективно. Равнотежне вредности за ВЛ и СГ су одрeђене преко Пелеговог модела. Поред тога, енергија активације за ВЛ и СГ је одређена преко Пелегове константе брзине и Аренијусове једначине. Кључне речи: Пелегов модел, осмотска дехидратација, меласа шећерне репе Received 31 August 2011 Accepted 7 November