MASS TRANSFER IN BANANA CHIPS DURING OSMOTIC DEHYDRATION

The effects of temperature ( 50, 60 and 70 °C ), sucrose concentration ( 50, 60 and 70° Brix ) and pH ( 6,7 and 8 ) on the mass transfer during osmotic dehydration of banana chips were studied. Fitting a diffusion model gave apparent diffusivity values varied from 2.77 to 2.66 × 10^-9 m² s^-1 and depending on temperature and sucrose concentration but not on pH changes. The effct of syrup/product volume ratio on the mass transfer kinetics was also investigated.     

TEMPERATURE AND CONCENTRATION EFFECTS OF OSMOTIC MEDIA ON OD PROFILES OF SWEET POTATO CUBES

A study was conducted to evaluate the effects of temperature and sucrose osmotic solution concentrations on osmotic dehydration profiles of sweet potato (Ipomea batata) cubes (3.5 cm sides). Two temperatures (26 and 50°C) and three concentrations (30:100, 50:100 and 70:100 w/w) were studied for various exposition times, up to 168 hours. Main influence was observed at higher temperature (50°C) due the fact that water loss (WL) and solids gains (SG) are faster and more intense. At 26°C no appreciable change in solids concentration was observed at distances deeper than 0.5 cm from the cubes surfaces even at 168 hours. At 50°C all the layers are affected even at shorter times (8 hours).     

Optimization of Osmotic Dehydration of Kiwifruit

Mass transfer rates were quantitatively investigated during osmotic dehydration of kiwifruit slices using response surface methodology with the sucrose concentration (20-80%, w/w), temperature of sucrose solution (15-75°C), osmotic time (60-420 min), and slice thickness (2-10 mm) as the independent process variables. Quadratic regression equations are obtained to describe the effects of independent process variables on the water loss (WL), sucrose gain (SG), and ascorbic acid loss (AAL). It was found that all factors had significant effect on the WL during osmotic dehydration of kiwifruit. Effects of temperature, time, and slice thickness were more pronounced on SG than the effect of concentration of sucrose solution. The osmotic solution temperature was the most significant factor affecting the AAL, followed by slice thickness and duration of treatment. The optimal conditions for osmotic dehydration were: 60% sucrose concentration, 30-40°C osmotic temperature, 150 min osmotic time, and 8 mm slice thickness.     

Control of Polyphenol Oxidase Activity in Banana Slices During Osmotic Dehydration

The purpose of this study was to determine the effect of sodium metabisulfite and 4-hexylresorcinol on polyphenol oxidase (PPO) activity change in banana slices during osmotic dehydration in sucrose syrup.

From a previous study only three osmotic dehydration conditions were selected as the most adequate due to color change but also where PPO residual activity was still present after osmotic drying: T1 (60°Bx, 50°C, pH 6), T2 (60°Bx, 60°C, pH 8), and T3 (70°Bx, 50°C, pH 8). The level of sodium metabisulfite was varied from 100 to 1000 ppm and 4-hexylresorcinol from 10 to 100 ppm. The inner and outer parts of the banana slice were used for PPO activity determination at 302 nm with 4 methyl-catechol as a substrate.

During osmotic dehydration of a banana slice, PPO activity tended to decrease and residual enzymatic activity was still detected. Sodium metabisulfite concentration up to 200 ppm and 4-hexylresorcinol up to 50 ppm had no effect on PPO residual activity after 4 h of osmotic dehydration. Depending on the process conditions, a higher concentration of additives than these were necessary to control PPO activity during osmotic dehydration of banana slices.     

EQUILIBRIUM CONCENTRATION AND WATER AND SUCROSE DIFFUSIVITY IN OSMOTIC DEHYDRATION OF PINEAPPLE SLABS

The weight and water loss of 6 mm thick pineapple slabs (one of a six part of slice) were analyzed during osmotic dehydration in sucrose solution at different temperatures (50, 60 and 70°C), sucrose concentrations (50, 60 and 70°Bx) and pH's (6, 7 and 8), in 3³ experimental design. These results were fitted to a modified Azuara equation to obtain water and sucrose diffusivity results at equilibrium condition. Mean result of water diffusivity was 1.717 × 10^-5 cm²/s and sucrose diffusivity varied from 2.0 to 4.6 × 10^-5 cm²/s. The results of water loss at equilibrium in pineapple slabs varied between 0.6 to 0.67 g/g of initial sample weight. The results of sucrose gain at equilibrium varied between 0.15 and 0.21 g/g of initial sample weight. The results from mathematical modeling were compared to experimental results with r² = 0.94.     

MASS TRANSFER IN BANANA CHIPS DURING OSMOTIC DEHYDRATION

ABSTRACT

The effects of temperature ( 50, 60 and 70 °C ), sucrose concentration ( 50, 60 and 70° Brix ) and pH ( 6,7 and 8 ) on the mass transfer during osmotic dehydration of banana chips were studied. Fitting a diffusion model gave apparent diffusivity values varied from 2.77 to 2.66 × 10^?9 m² s^?1 and depending on temperature and sucrose concentration but not on pH changes. The effct of syrup/product volume ratio on the mass transfer kinetics was also investigated.     

Optimization of Osmo-convective Dehydration Process for the Development of Honey-ginger Candy Using Response Surface Methodology

Osmotic dehydration of ginger with honey is an interesting alternative for the development of confectionary-based functional food with extended shelf life. Response surface methodology (RSM) was used to investigate the effects of process variables on solid gain, water loss, and overall acceptability of honey-ginger candy. The process variables included blanching time (6–10 min), osmotic solution temperature (30–50°C), immersion time (90–150 min), and convective drying temperature (50–70°C). The honey to ginger ratio was 4:1 (w/w) during all the experiments. Ginger cubes were blanched before osmotic dehydration to increase the permeability of the outer cellular layer of tissue. After osmotic concentration of ginger with honey, convective dehydration was done to final moisture content of 3–5% (w.b.) to make it a shelf-stable product. Finally, osmo-convectively dried ginger was coated with sucrose for candy preparation. The optimum osmo-convective process conditions for maximum solid gain, water loss, and overall acceptability of honey-ginger candy were 7.07 min blanching time, 50°C solution temperature, 150 min immersion time, and 60°C convective drying temperature.     

EFFECT OF OSMOTIC AGENT ON OSMOTIC DEHYDRATION OF FRUITS

Mass transfer phenomena were investigated during osmotic dehydration of apple, banana and kiwi in glucose and sucrose osmotic solution. A complete set of experiments was performed for a wide range of temperature, sample size, speed of agitation, osmotic agent concentration and immersion time. An empirical model, based on a first order kinetic equation, was fitted satisfactorily to experimental data. Furthermore, the effect of solute molecular weight on mass transfer phenomena during the osmotic treatment was evaluated. The results showed that low molecular weight solute (glucose) leads to higher water loss and solids uptake than high molecular weight solute (sucrose), of osmodehydrated fruits under the same solution concentration.     

Kinetic Aspects, Texture, and Color Evaluation of Some Tropical Fruits during Osmotic Dehydration

Osmotic dehydration of some tropical fruits like guava, melon, and papaya using sucrose and maltose solutions is presented in this article. The influence of sugar type and concentration, process temperature, and calcium salt addition on osmotic solution was investigated. Water loss and sugar gain up to 6 h of processing were evaluated and the effect of osmotic dehydration on fruit quality parameters like color and texture was analyzed. All studied variables affected the osmotic process kinetics, while for quality parameters the influence of sugar type or solution concentration and temperature was dependent on fruit and process conditions.     

EFFECT OF OSMOTIC AGENT ON OSMOTIC DEHYDRATION OF FRUITS

ABSTRACT

Mass transfer phenomena were investigated during osmotic dehydration of apple, banana and kiwi in glucose and sucrose osmotic solution. A complete set of experiments was performed for a wide range of temperature, sample size, speed of agitation, osmotic agent concentration and immersion time. An empirical model, based on a first order kinetic equation, was fitted satisfactorily to experimental data. Furthermore, the effect of solute molecular weight on mass transfer phenomena during the osmotic treatment was evaluated. The results showed that low molecular weight solute (glucose) leads to higher water loss and solids uptake than high molecular weight solute (sucrose), of osmodehydrated fruits under the same solution concentration.     

TEMPERATURE AND CONCENTRATION EFFECTS OF OSMOTIC MEDIA ON OD PROFILES OF SWEET POTATO CUBES

A study was conducted to evaluate the effects of temperature and sucrose osmotic solution concentrations on osmotic dehydration profiles of sweet potato (Ipomea batata) cubes (3.5 cm sides). Two temperatures (26 and 50°C) and three concentrations (30:100, 50:100 and 70:100 w/w) were studied for various exposition times, up to 168 hours. Main influence was observed at higher temperature (50°C) due the fact that water loss (WL) and solids gains (SG) are faster and more intense. At 26°C no appreciable change in solids concentration was observed at distances deeper than 0.5 cm from the cubes surfaces even at 168 hours. At 50°C all the layers are affected even at shorter times (8 hours).     

Effect of Blanching by Ohmic Heating on the Osmotic Dehydration Behavior of Apple Cubes

The effect of blanching by ohmic heating (OH) on the damage to apple tissues and subsequent osmotic dehydration kinetics was investigated. Apple cubes were heated ohmically to various blanching scales. Heating temperature and duration were, respectively, 60–95 ± 2°C and 0–6 min. After cooling, the treated samples were put into sucrose solutions (70 °B) for the osmotic dehydration (OD). The equilibrium state of osmotic dehydration was estimated using the Azuara model. Ohmic heating leads, even for short treatments, to significant changes in the cellular structure of apples and to the enhancement of mass transfer during osmotic dehydration.     

Thin Layer Drying Models for Osmotically Pre-dried Young Coconut

Thin layer convection drying was performed on osmotically pre-dried young coconut, strips, both thin and thick. A drying air temperature range of 50-70°C and an airflow of 0.25 m s^-1 was used to dry samples soaked in three sugar solution concentrations (40, 50, and 60°B) during the osmotic drying phase, with the convection drying alone serving as control. An analysis of variance (ANOVA) revealed that sugar concentration and thickness significantly affected osmotic drying rates as shown by their final moisture contents. While the drying air temperature and slab thickness significantly affected the average drying rate and the sugar concentration was an insignificant factor during convective drying phase. Effective diffusivity of water during hot air drying varied from 1.71 to 5.51 × 10^-10 m²s^-1 over the temperature range investigated, with energy of activation equal to 1173.0 kJ/kg. Three mathematical models available in the literature were fitted to the experimental data, with the Page model giving better predictions than the single or double term exponential model. The temperature dependence of the diffusivity coefficients was satisfactorily described by a simple Arrhenius type relationship.     

POLYPHENOL OXIDASE ACTIVITY IN BANANA CHIPS DURING OSMOTIC DEHYDRATION

Various treatments were used to determine polyphenol oxidase activity changes during osmotic dehydration of banana slices. A temperature of 35 °C and 5.0 pH were used as the most adequate conditions for polyphenol oxidase activity determination when 4-methyl catechol was used as a substrate. Enzyme activity change was determined in the central and edge region of fruit. The central part of the banana slice showed 2.4 times higher activity than in the edge region. A difference in the kinetics of enzyme activity decrease also occurred during four hours of drying. When the drying was carried out at 70 °C, the enzyme was completely inactivated after 60-90 minutes of specific osmotic treatments. After four hours of osmotic drying at 50 and 60 °C, polyphenol oxidase activity was still present; the residual activity varied from 1.3 to 15 %.     

Osmotic Dehydration of Apple Cylinders: III. Continuous Medium Flow Microwave Heating Conditions

Continuous flow osmotic drying permits a better exchange of moisture and solids between the food particle and osmotic solution than the batch process. Osmotic drying has been well studied by several researchers mostly in the batch mode. Microwave heating has been traditionally recognized to provide rapid heating conditions. Its role in the finish drying of food products has also been recognized. In this study, the effects of process temperature, solution concentration on moisture loss (ML), solids gain (SG), and mass transport coefficients (k_m and k_s) were evaluated and compared under microwave, assisted osmotic dehydration (MWOD) versus continuous flow osmotic dehydration (CFOD). Apple cylinders (2 cm diameter, 2 cm height) were subjected to continuous flow osmotic solution at different concentrations (30, 40, 50, and 60°Brix sucrose) and temperatures (40, 50, and 60°C). Similar treatments were also given with samples subjected to microwave heating. Results obtained showed that solids gain by the samples was always lower when carried out under microwave heating, while the moisture loss was increased. The greater moisture loss strongly counteracted solids gain in MWOD and thus the overall ratio of ML/SG was higher in MWOD than in CFOD.     

OPTIMIZATION OF THE OSMOTIC DEHYDRATION OF MANGO (MANGIFERA INDICA L.) SLICES

Fresh mango (Mangifera indica) slices were osmotically dehydrated using four treatment variables: treatment time, temperature, sugar concentration and slice thickness. Treatment times for 2, 4 and 6 mm slice thickness were 3, 5 and 7 h at temperatures of 20, 30 and 40°C and sugar concentrations of 40, 50 and 60% (w/w). The responses variables tested were weight reduction (WR), sugar gain (SG), final moisture content (M_f) and overall product acceptability (OA). A fractional factorial design (3 level-4 parameter) with 27 runs was used as the experimental design.

A Response Surface Methodology (RSM) was performed to analyze and predict the optimum conditions of the mango osmotic dehydration process. All treatment variables significantly affected WR, while SG and M_f were significantly affected only by thickness. On the other hand, none of the variables showed no significant effect on the OA.

The optimum conditions were determined with the following response limiting values: at least 30% WR, at least 8% in SG, M_f of not exceeding 70% were based on previous studies and panel evaluation results. The optimum conditions generated were: treatment time of 6 h, temperature of 35°C, sugar concentration of 65% (w/w) for 5 mm slice thickness. Results of validation tests were fairly acceptable since the Coefficient of Variation (CV) of the responses were less than 15% except for sugar gain with a 26.5% CV.     

INFLUENCE OF SOLUTE TEMPERATURE AND CONCENTRATION ON THE COMBINED OSMOTIC AND AIR DRYING

The effect of solute concentration (15-45 % sugars) and temperature (10-40 °C) on the osmotic dehydration of apple was investigated. Cylindrical samples of apple were immersed in glucose or sucrose solutions and the water loss, the volume of solids and the porosity were measured as a function of time. Water loss was proportional to the square root of time, while the volume of solids decreased and the porosity increased with time. Sugar gain and water loss decreased the compression stress of the apple samples. Osmotic pre-treatment reduced the shrinkage and the porosity of apple solids during air-drying, compared to the no-treated samples. The results of this investigation are useful in the design of efficient osmotic dehydration processes, and in the evaluation of texture of dehydration of products.     

Mathematical Equations to Predict Mass Fluxes and Compositional Changes During Osmotic Dehydration of Cherry Tomato Halves

Cherry tomato halves (L. esculentum var. Cerasiforme cv. Cocktail) were dehydrated by immersion in binary solutions of salt or sugar and ternary salt-sugar solutions at 30, 40, and 50°C. Compositional changes (moisture, sugar, and salt content) as well as mass fluxes were controlled at different process times. The influence of temperature and osmotic agents (salt, sucrose, and the combination of them) on mass transfer phenomena was studied, and the experimental results were modeled in order to establish a set of equations that would facilitate the prediction not only of final product composition, which is related to its quality and its stability, but also the mass fluxes involved in the process associated to the yield of the process.     

果蔬渗透脱水过程动力学研究

结合植物组织结构与流体传输过程机理建立了渗透脱水过程的一维质量传递数学模型。模型以植物细胞为传输过程的基本单元，考虑了各组分在细胞内、细胞外、通过细胞膜及胞间连丝的质量扩散，和由于体积收缩而导致的集流传输。以土豆为实验物料，在40℃恒温条件下，采用40％（质量百分比）的蔗糖溶液作为渗透液，进行渗透脱水实验，得到的实验结果与模拟结果十分接近，验证了模型的有效性。通过数值模拟可详细描述渗透脱水过程中土豆细胞内外水和蔗糖的质量浓度分布。并就能源与生产效率方面对“渗透-干燥”与“无预处理干燥”过程作了比较。     

Influence of osmotic dehydration process parameters on the quality of candied pumpkins

The influence of osmotic dehydration process parameters on the efficiency of water loss and sucrose gain of pumpkins and the influence on the quality of the final product are essential for production of superior quality candied pumpkins. Mass transfer kinetics during osmotic dehydration of pumpkins were modelled by assuming Fickian diffusion of sucrose and water in unsteady state conditions, which described very well the experimental results for water loss and sugar gain. Water and sucrose effective diffusion coefficients increase significantly with temperature. Temperature and sucrose concentration had a significant influence on both water and sugar diffusion, increasing as the solution temperature increased. Significant increase in the effective water diffusivity and decrease in the sucrose effective diffusivity was observed when the sucrose solution concentration increased from 40 °Brix to 50 and 60 °Brix. From 50 to 60 °Brix, no difference in the effective diffusivities was observed. Candied pumpkins with higher sucrose content have a higher breaking stress, less breaking strain and lower work to fracture. Moreover, the product becomes harder and less elastic with increasing sucrose content, resulting in more brittle products, which seems to be related with reinforcement of the pumpkin cell wall matrix.