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.     

VACUUM OSMOTIC DEHYDRATION OF FRUITS

Vacuum osmotic dehydration leads a special behaviour of mass transfer in fruit-sugar soluion system.Vacuum treatments intensify the capillary flow function and increase water transfer ratio.but have no significant influence on sugar uptake.Fruits such as pineapples which have higher porosity are more suitable to be treated under vacuum during the osmotic dehydration.     

VACUUM OSMOTIC DEHYDRATION OF FRUITS

ABSTRACT

Vacuum osmotic dehydration leads a special behaviour of mass transfer in fruit-sugar soluion system.Vacuum treatments intensify the capillary flow function and increase water transfer ratio.but have no significant influence on sugar uptake.Fruits such as pineapples which have higher porosity are more suitable to be treated under vacuum during the osmotic dehydration.     

EFFECT OF PROTEOLYTIC ENZYMES ON COLOR CHANGES IN BANANA CHIPS DURING OSMOTIC DEHYDRATION

ABSTRACT

The effect of papain and microbial Multifect P -- 3000 on color parameter changes: L, hue and chroma in banana slices (border and central part) during four hours of osmotic dehydration were studied. These enzymes did not control color changes in banana slices and were not found on the surface of dehydrated chips. Neither papain nor Multifect P -- 3000 should be used during osmotic dehydration to control browning in banana chips.     

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.     

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.     

EFFECT OF EDTA ON COLOR DURING OSMOTIC DEHYDRATION OF BANANA SLICES

Five conditions of the osmo-dehydration process of banana slices, which in our previous study underwent the most adequate color parameters changes were used with the presence of EDTA added to the syrup solutions at five concentrations of 0.01, 0.05, 0.1, 0.5 and 1% w/w. EDTA presence did not change the tendency of polyphenol activity decrease during osmotic drying as well as has not effect on chroma, hue and total color difference changes. EDTA presence had an effect on L value decrease in the inner and outer part of the slice, and did not depend to osmotic dehydration conditions. It is highly recommended to use EDTA during osmotic dehydration of some fruits that would undergo undesirable darkening.     

EFFECT OF CHITIN ON COLOR DURING OSMOTIC DEHYDRATION OF BANANA SLICES

ABSTRACT

Five conditions of the osmo-dehydration process of banana slices, which in our previous study underwent the most adequate color parameter changes. L, hue and chroma values were studied with the presence of chitin added to the syrup solutions at the concentration of 0.05, 0.1 and 0.5% w/w. After four hours of osmo-dehydration, color space results of L, a and b as well as polyphenol oxidase activity were measured. Color space results were used to calculate hue and chroma and total color difference changes. Chitin presence did not change the tendency of polyphenol activity decreased during osmotic drying as well as has not effect on chroma, hue and total color difference changes. Chitin presence had an effect on L value decrease in the inner and outer part of the slice, and these changes did not depend to osmotic dehydration conditions. It is highly recommended to use chitin during osmotic dehydration of some fruits that would undergo undesirable darkening.     

EFFECT OF OSMOTIC DEHYDRATION ON VISCOELASTIC PROPERTIES OF APPLE AND BANANA

The rheological behavior of osmotically dehydrated apple and banana was examined under uniaxial compression and relaxation tests of cylindrical specimens. Compression and relaxation tests were performed, following air drying of osmotically pre-treated samples, at various moisture contents ranging from 0.1 to 1.5 kg/kg dry basis. The maximum stress and the corresponding strain were correlated to the moisture content using simple mathematical equations. It was shown that both parameters increase as water was removed and their values are significantly higher than the corresponding values for untreated air dried samples. The effect of moisture content on compressive behavior of osmotically dried materials was introduced through its effect on the four model parameters: the maximum stress (σ_max) the maximum strain (ε_max), the elastic parameter (E) and the viscoelastic exponent (p). The stress relaxation data of osmotically treated samples were modeled using a two-term Maxwell model. It was shown that osmotic pre-treatment increased the remaining force and it decreased the relaxation time of dehydrated samples. The osmotic dehydration and therefore the sugar gain tend to increase the viscous nature of fruits and decrease their elasticity for both materials, causing plasticity of the structure.     

EFFECT OF CHITIN ON COLOR DURING OSMOTIC DEHYDRATION OF BANANA SLICES

Five conditions of the osmo-dehydration process of banana slices, which in our previous study underwent the most adequate color parameter changes. L, hue and chroma values were studied with the presence of chitin added to the syrup solutions at the concentration of 0.05, 0.1 and 0.5% w/w. After four hours of osmo-dehydration, color space results of L, a and b as well as polyphenol oxidase activity were measured. Color space results were used to calculate hue and chroma and total color difference changes. Chitin presence did not change the tendency of polyphenol activity decreased during osmotic drying as well as has not effect on chroma, hue and total color difference changes. Chitin presence had an effect on L value decrease in the inner and outer part of the slice, and these changes did not depend to osmotic dehydration conditions. It is highly recommended to use chitin during osmotic dehydration of some fruits that would undergo undesirable darkening.     

EFFECT OF OSMOTIC DEHYDRATION ON VISCOELASTIC PROPERTIES OF APPLE AND BANANA

ABSTRACT

The rheological behavior of osmotically dehydrated apple and banana was examined under uniaxial compression and relaxation tests of cylindrical specimens. Compression and relaxation tests were performed, following air drying of osmotically pre-treated samples, at various moisture contents ranging from 0.1 to 1.5 kg/kg dry basis. The maximum stress and the corresponding strain were correlated to the moisture content using simple mathematical equations. It was shown that both parameters increase as water was removed and their values are significantly higher than the corresponding values for untreated air dried samples. The effect of moisture content on compressive behavior of osmotically dried materials was introduced through its effect on the four model parameters: the maximum stress (σ_max) the maximum strain (?_max), the elastic parameter (E) and the viscoelastic exponent (p). The stress relaxation data of osmotically treated samples were modeled using a two-term Maxwell model. It was shown that osmotic pre-treatment increased the remaining force and it decreased the relaxation time of dehydrated samples. The osmotic dehydration and therefore the sugar gain tend to increase the viscous nature of fruits and decrease their elasticity for both materials, causing plasticity of the structure.     

EFFECT OF EDTA ON COLOR DURING OSMOTIC DEHYDRATION OF BANANA SLICES

ABSTRACT

Five conditions of the osmo-dehydration process of banana slices, which in our previous study underwent the most adequate color parameters changes were used with the presence of EDTA added to the syrup solutions at five concentrations of 0.01, 0.05, 0.1, 0.5 and 1% w/w. EDTA presence did not change the tendency of polyphenol activity decrease during osmotic drying as well as has not effect on chroma, hue and total color difference changes. EDTA presence had an effect on L value decrease in the inner and outer part of the slice, and did not depend to osmotic dehydration conditions. It is highly recommended to use EDTA during osmotic dehydration of some fruits that would undergo undesirable darkening.     

EFFECT OF OSMOTIC DEHYDRATION ON COLOR AND SORPTION CHARACTERISTICS OF APPLE AND BANANA

Color and sorption characteristics of osmotically treated and air dried apple and banana were studied during air drying at 70^°C. The color parameters: Lightness (L), Redness (a) and Yellowness (b) were studied, using a Hunter Lab chromatometer. A first order kinetic model was fitted to the experimental data adequately for color parameters, while sorption data for treated and air dried products were fitted to the GAB model. Untreated fruits showed an extensive browning which was monitored by a significant drop of the lightness (L) and an increase of redness (a) and yellowness (b). Osmotically pretreated samples did not brown as much as the untreated samples and the lightness L decreased only slightly while a, b increased slightly. Osmotic pretreatment resulted in a shift in sorption isotherm for both fruits. Osmotic dehydration prevented color damages and decreased the sorption capacity of dehydrated products.     

EFFECT OF OSMOTIC DEHYDRATION ON COLOR AND SORPTION CHARACTERISTICS OF APPLE AND BANANA

ABSTRACT

Color and sorption characteristics of osmotically treated and air dried apple and banana were studied during air drying at 70^°C. The color parameters: Lightness (L), Redness (a) and Yellowness (b) were studied, using a Hunter Lab chromatometer. A first order kinetic model was fitted to the experimental data adequately for color parameters, while sorption data for treated and air dried products were fitted to the GAB model. Untreated fruits showed an extensive browning which was monitored by a significant drop of the lightness (L) and an increase of redness (a) and yellowness (b). Osmotically pretreated samples did not brown as much as the untreated samples and the lightness L decreased only slightly while a, b increased slightly. Osmotic pretreatment resulted in a shift in sorption isotherm for both fruits. Osmotic dehydration prevented color damages and decreased the sorption capacity of dehydrated products.     

OSMOTIC DEHYDRATION OF PINEAPPLE

The effects of sugar type, sugar concentration, immersion time and temperature on the mass transfer of osmotic dehydration were studied using pie shape slices (7 mm thick with its center cork thrown away) of fresh pineapple (Queen variety, 90% maturity). The dehydration process was performed using two type of sugar as an osmotic agent (glucose and sucrose), three levels of sugar concentration (50, 60, and 70%), three levels of temperature (30, 50, and 70 °C), and three levels of immersion time (3, 6, and 9 hours). Following the osmotic dehydration process, the pineapple was dried at 70 °C for 48 hours. The mass transfer was then calculated and analyzed statistically. Sugar type, concentration, temperature, and length of immersion, have a significant effect on the mass transfer of osmotically dehydrated pineapple. The highest mass transfer of pineapple was found by using sucrose at the concentration of 70%, temperature 50 °C and 9 hours of immersion time.     

POLYPHENOL OXIDASE ACTIVITY IN BANANA CHIPS DURING OSMOTIC DEHYDRATION

ABSTRACT

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 %.     

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 KINETICS OF BLUEBERRIES

Abstract

The kinetics of moisture loss and solids gain during osmotic dehydration of blueberries under different conditions of temperature (37°C - 60°C), concentration of the sucrose solution (47°Brix - 70°Brix) and contact time between fruit and sucrose solution (0.5 h - 5.5 h) were studied, and modeled based on Fick's law of unsteady state diffusion. The study showed that all factors influenced moisture loss and solids gain (p<0.001), both generally increasing with temperature (T) and sucrose concentration (C). Based on the diffusion model, the calculated effective moisture diffusivity (D_m) ranged from 1.98 × 10^?10 to 5.10 × 10^?10 m²/s and the effective solids diffusivity (D_s) ranged from 2.54 × 10^?11 to 2.22 × 10^?10 m²/s. Both D_m and D_s showed increasing trends with temperature and sucrose concentration, and could be modeled as quadratic functions of T and C.     

INFLUENCE OF OSMOTIC DEHYDRATION ON TEXTURE AND PECTIC COMPOSITION OF KIWIFRUIT SLICES

ABSTRACT

In order to optimize the osmotic dehydration process as a pre-treatment to freezing, chemical and structural characteristics of the raw fruit have to be studied together with their influence on the solid liquid exchanges and on the quality of the end products

Textural properties of fruits are intimately associated with the cellular structure and pectic composition. So the influence of osmodehydration on the modification of texture and water-soluble, oxalate-soluble and residual protopectin in kiwifruit slices was studied. To determine the optimum firmness level of the raw kiwifruit, the fruits were processed at three instrumentically measured texture levels: firm, medium and soft. Chemical and physical analyses showed that the biggest difference among the three groups of fresh kiwifruit was the protopectin content which was correlated directly with texture. No relationships were found between texture changes and pectic composition during osmodehydration, the slight firmness increase probably being produced by the soluble solids concentration.     

INFLUENCE OF OSMOTIC DEHYDRATION ON TEXTURE AND PECTIC COMPOSITION OF KIWIFRUIT SLICES

In order to optimize the osmotic dehydration process as a pre-treatment to freezing, chemical and structural characteristics of the raw fruit have to be studied together with their influence on the solid liquid exchanges and on the quality of the end products

Textural properties of fruits are intimately associated with the cellular structure and pectic composition. So the influence of osmodehydration on the modification of texture and water-soluble, oxalate-soluble and residual protopectin in kiwifruit slices was studied. To determine the optimum firmness level of the raw kiwifruit, the fruits were processed at three instrumentically measured texture levels: firm, medium and soft. Chemical and physical analyses showed that the biggest difference among the three groups of fresh kiwifruit was the protopectin content which was correlated directly with texture. No relationships were found between texture changes and pectic composition during osmodehydration, the slight firmness increase probably being produced by the soluble solids concentration.