Osmotic Dehydration Of Apples Research Articles

Influence of temperature and solute concentration during osmotic dehydration of apple (Malus domestica) cubes on the stability of probiotics

Currently, there is an upsurge in preference for the consumption of probiotic-rich foods. Besides their nutritive function, these compounds have demonstrated, in some instances, medicinal properties. The purpose of this study was to evaluate how temperature and sucrose concentration influenced the stability of probiotics (specifically Saccharomyces boulardii) during the osmotic dehydration of Granny Smith apple (Malus domestica) cubes. We prepared osmotic solutions with different sucrose concentrations (40, 50, and 60°Brix). We inoculated S. boulardii (250 mg each) into these solutions, followed by immersion of 1 cm-cubed apple cubes. We exposed these cubes to varying temperatures (37°C, 42°C, and 47°C) for a duration of 80 min. Various parameters were calculated, including the percentage of weight loss, percentage of solid gain, number of generations, and the doubling time. Results indicated that the apple cubes with more extreme dehydration were those treated at 50°Brix and 47°C exhibiting a weight loss of 40%. The treatment at 60°Brix and 42°C stood out, showing an increase of 350% of solid gain compared to other groups. Additionally, the highest number of generations of the strain occurred in the group treated at 50°Brix and 37°C, with a value of 9.32 ± 0.11 CFU/g and a doubling time of 7.50 ± 0.09 min. In conclusion, we deduced that under conditions of elevated temperatures and high solute concentrations, the S. boulardii strain might undergo inhibition and fail to develop adequately in the apple cubes subjected to osmotic dehydration.

Increase of mass transfer rates during osmotic dehydration of apples by application of moderate electric field

Abstract Osmotic dehydration (OD) is a drying process that consists in placing the food in contact with concentrated solutions of soluble solids to reduce its water activity. The use of moderate electric field (MEF) may promote increase of the mass transfer rates due to the non-thermal effects of electroporation and permeabilization of the cells. In this context, the objective of this study was to investigate the mass transfer process kinetics during apples OD assisted by MEF, evaluating the non-thermal effects of this emerging technology. The experiments were conducted with sucrose solutions (40, 50 and 60%, m/m) at 40 °C. Samples were submitted to electrical field strength (0, 5.5 and 11.0 Vcm−1), according to an experimental design. Results indicated that the application of MEF favoured water loss and solid gain. The effective mass diffusivities of water and solids increased as voltage applied increases. Moreover, MEF negatively influenced color and reducing capacity of the samples.

Modeling of solute transport inside plant tissue during osmotic dehydration of apple

The accumulation of solutes on the food surface has resulted in notable contradictions between data resulting from modeling and information observed experimentally. Hence, the mechanisms involved in the transport of solutes in the plant tissue during osmotic dehydration (OD) have not been well documented. The purpose of this study was to analyze solute concentration at different depths of osmotically dehydrated apple cylinder with the use of a conventional (sucrose) and a non-conventional (stevia) osmotic agent. Solute concentration was modeled by Fick's law in order to identify the thicknesses within the tissue where the solute is transferred under a diffusive mechanism. Samples were dehydrated in sucrose (30 and 50°Brix) and stevia (3 and 6% w/w) aqueous solutions. Samples were cut in five slices (0.5, 2, 4, 7, 10 mm in z direction) from the surface to the food center. Sample properties such as: water loss, solute gain, moisture content, solute concentration and effective diffusivity coefficients at different tissue depths and time periods of dehydration process were determined. Results showed the concentration of solutes was higher in the surface than the center for both osmotic solutions: stevia and sucrose. Fick model did not allow an adequate description of the experimental data in the area of solutes accumulation, suggesting that transfer of solutes on the tissue surface is governed by other transport mechanism different from diffusion. This result opens new ways for future research of the solutes transport within plant tissue. Under this approach, the surperficial impregnation of solutes at the surface and a diffusive phenomenon inside the sample center could be considered.

Osmotic dehydration of apple and pear slices: color and chemical characteristics

Abstract Osmotic dehydration is the pre-treatment method of preservation the fruits and vegetables to increase their shelf life. This method consists of immersing fruits and vegetables in concentrated solutions of salt or sugar. The effect of osmotic dehydration was investigated on the color and chemical characteristics of dehydrated fruits (apple and pear) in fructose osmotic solutions. Difference in CIE-LAB, chroma - C* and hue angle H* were performed with a Chroma Meter CR-400/410. Apple (Malus domestica ‘Jonathan’) and sweet autumn pear variety (Pyrus comunis) were osmotically dehydrated in three aqueous solution of fructose (40, 60 and 80%), during 3 h of process at temperatures of 20 °C, with fruit/osmotic agent ratio of 2:1. Water loss and solids gain showed significant differences depending on the concentration of the osmotic agent and process time. The use of highly concentrated osmotic solutions induced losses of phenolic content (TPC) and ascorbic acid in the sliced apples and pears. Fructose concentration and osmosis time induce significant increase of a* and b* colorimetric parameters but did not affect the lightness (L*) of pear slices.

Structural properties and solute transfer relationships during sucrose and stevia osmotic dehydration of apple

The objective of this research was determined the structural changes in plant tissue during osmotic dehydration (OD) of apple in stevia and sucrose aqueous solutions. Macro and microstructural properties at different thicknesses of the sample were determined. For the study of structural properties, samples were cut in five slices at different thicknesses (0.5, 2, 4, 7, 10 mm in z direction) from the surface to the sample center. Anhydrous real density, volume and microscopy images in sample slices were determined and its relationship with the transfer of water and solutes inside the tissue were analyzed. Anhydrous real density in food considering the solids density in the sample was determined. Volume change as a function of moisture migration in the sample was evaluated. Apple samples were immersed into sucrose (30 and 50° Brix) and stevia (3 and 6%) osmotic solutions at 30 °C and 50 °C. The results showed an increase in the anhydrous real density in the area of greater loss of moisture and greater accumulation of solutes within the food. The volume increased in the thicknesses of the center of the sample where the moisture concentration was highest. The greatest alterations of the plant cell structure in the surface of the sample were observed.

The impact of using polyols as osmotic agents on mass exchange during osmotic dehydration and their content in osmodehydrated and dried apples

The purpose of this study was to evaluate the possibility of using polyols (erythritol, xylitol, and maltitol) as alternatives to sucrose commonly used for osmotic dehydration (OD) of apples and to determine their content in osmotically dehydrated and dried fruit. For comparison, apples were also dehydrated in a sucrose solution. The content of sugars (sucrose, fructose, and glucose) was determined as well. Osmotic dehydration was examined at a temperature of 40 °C in time ranges between 15 and 360 min, and also 1440 min. The polyol solutions were equally or significantly more effective in the OD of apples compared to the sucrose solution. Regardless of the type of osmotic solution, the water loss of apples was from 2 to 10 times greater than solid gain. The color of fruit dehydrated in sucrose and xylitol solutions was characterized by the smallest total color difference (7.9–10.5) compared with the fresh apple tissue. Osmotic dehydration of apples in polyol solutions resulted in the transfer of these substances to fruit tissue. Erythritol was the most effective osmotic agent. The use of polyols for the OD of fruit at the pretreatment stage and the appropriate drying method can be used to create products with high qualities among others due to the lack of added sugars. The use of hybrid drying after the osmotic treatment is a good alternative to the freeze-drying process.

Experimental investigation of effective factors of pulsed electric field in osmotic dehydration of apple

The effects of various factors of the pulsed electric field (PEF) as an apple osmotic dehydration (OD) preprocess by using response surface methodology (RSM) are investigated and optimized in this paper. Electric field strength, pulse numbers and pulse duration were considered as PEF pretreatment effective factors in constant osmotic dehydration conditions such as concentration and temperature. After 4 h of osmosis, the results indicate decrease in amounts of water loss (WL) and solid gain (SG) by increasing field strength from 1 to 2 kV/cm and decreasing pulse duration from 0.5 to 0.02 s, respectively. The effect of increasing the pulse numbers from 8 to 16 give rise to the increase in amounts of water loss and solid gain at first and then by increasing to 24 pulses, the decrease in these amount has been evident. The ratio of water loss to solid gain (WL/SG) and response surface methodology (RSM) were used for optimization effects of PEF factors on the OD process. In optimal values of electric field strength, pulse numbers and pulse duration, the WL/SG ratio provided highest reduction sample mass.

Development of apple chips technology

For develop of apple chips technology without chemical preservation osmotic dehydration in cherry or apple juice concentrates or fructooligosaccharide solutions and convection drying were used. Studies included the effect of dehydration on the mass transfer in apples and the quality of the final product. The temperature, type of osmotic solution and its concentration were changeable. The fruit were tested on mass transfer indicators, stability (water activity), texture (breaking test) and nutritional value (polyphenol content, acidity). Sensory evaluation was also performed. On this basis, the verification of all options was made and the most acceptable samples were selected. Concentration of osmotic solutions at 25°Brix limited solids gain in apples. Under these conditions, the phenomenon of osmosis caused 8–10 times greater water loss than solids gain. Increasing the concentration of solutions up to 50°Brix had a significantly greater impact on mass exchange in apples, compared to increasing the temperature from 40 to 60 °C. Osmotic dehydration before drying did not significantly affect the water activity but increase of the temperature negatively affected on breaking force of the chips. Chips obtained by osmotic dehydration of apples in a cherry concentrate solution contained significantly more polyphenols, and were characterized by a higher acidity than the variants obtained by dehydration in concentrated apple juice. Furthermore, they were marked by red color which has been thought as part of the attractiveness of the product. The least sensory acceptable chips were prepared using osmotic pre-treatment in cherry concentrated juice solution with the addition of fructooligosaccharide.

Description of osmotic dehydration of apple using two-dimensional diffusion models considering shrinkage and variations in process parameters

ABSTRACTThe main purpose of this paper is to study osmotic dehydration of apple in water and sucrose solutions. The kinetics of water quantity and solid gain are described by two mathematical models using numerical solutions of the two-dimensional diffusion equation in Cartesian coordinates with boundary condition of third kind. For the first model, both the process parameters and the product dimensions have been considered constant. For the second model these quantities have been taken as variable. The numerical solutions have been obtained via the finite volume method with fully implicit formulation. Process parameter estimation, using experimental data, was obtained by an optimizer based on the inverse method. The third-kind boundary condition was shown to be appropriate in view of the fact that the resistances to mass flows on the product surface are not at all negligible. The temperature and concentration of the osmotic solution used in the experiments influenced significantly the kinetics of solid uptake and water quantity as well as the values of estimated parameters. Mathematical model which considers the variations in the process parameters and the product shrinkage presents good physical consistency and well describes the mass migrations.

Osmotic Dehydration of Apples Under Reduced Pressure Conditions

Abstract The aim of the study was to determine the effect of reduced pressure on the osmotic dehydration of apples. Tests were performed under vacuum of 8 kPa, 67 kPa, 80 kPa and under the atmospheric pressure (100 kPa). The samples were dehydrated in a sucrose solution with a concentration of 30°Bx, 50°Bx and 70°Bx. It has been shown that the effect of low pressure application depends significantly to the concentration of the osmotic solution. It has been found that the overall weight change significantly depend on the concentration of the solution, and after 3 hours of dehydration at a pressure of 80 kPa at solutions of 30°Bx, 50°Bx and 70°Bx total weight loss increased by 65%, 12% and 25% respectively, when compared to samples dehydrated at atmospheric pressure. From the studied variants of reduced pressure, the pressure of 80 kPa seems to be the optimal one, as evidenced by the lowest values of weight gain to water loss ratios for apples dehydrated in solutions of 50°Bx and 70°Bx.

Simulation of mass transfer during osmotic dehydration of apple: a power law approximation method

In this study, unsteady one-dimensional mass transfer during osmotic dehydration of apple was modeled using an approximate mathematical model. The mathematical model has been developed based on a power law profile approximation for moisture and solute concentrations in the spatial direction. The proposed model was validated by the experimental water loss and solute gain data, obtained from osmotic dehydration of infinite slab and cylindrical shape samples of apple in sucrose solutions (30, 40 and 50 % w/w), at different temperatures (30, 40 and 50 °C). The proposed model’s predictions were also compared with the exact analytical and also a parabolic approximation model’s predictions. The values of mean relative errors respect to the experimental data were estimated between 4.5 and 8.1 %, 6.5 and 10.2 %, and 15.0 and 19.1 %, for exact analytical, power law and parabolic approximation methods, respectively. Although the parabolic approximation leads to simpler relations, the power law approximation method results in higher accuracy of average concentrations over the whole domain of dehydration time. Considering both simplicity and precision of the mathematical models, the power law model for short dehydration times and the simplified exact analytical model for long dehydration times could be used for explanation of the variations of the average water loss and solute gain in the whole domain of dimensionless times.

Correction of moisture and sucrose effective diffusivities for shrinkage during osmotic dehydration of apple in sucrose solution

Shrinkage, moisture and sucrose effective diffusivities were correlated for infinite slab shape samples of apple during osmotic dehydration in sucrose solution. Experiments were carried out in the sucrose solutions of different concentrations (30%, 40% and 50%) and temperatures (30°C, 40°C and 50°C). The two parameter model, developed by Azuara et al. (1992), was used to predict water loss and solid gain at equilibrium condition. Moisture and sucrose diffusivities were estimated by fitting the experimental moisture loss and solid gain data to the modified form of Fick's second law of diffusion, considering the shrinkage of the apples during osmotic dehydration. Results showed that the volume of the samples decreased linearly with water loss (WL) and weight reduction (WR). For above conditions of osmotic dehydration, effective diffusivities without considering the shrinkage were found to be in the range of 1.36×10−10 m2/s–2.00×10−10 m2/s, and those with considering the shrinkage were in the range of 0.87×10−10 m2/s–1.27×10−10 m2/s. The values of the effective diffusivities estimated by considering the shrinkage were smaller than those without considering this phenomenon.

Modeling of Water Loss during Osmotic Dehydration of Apple Cubes in Sugar Beet Molasses

Application of the Peleg model was investigated for predicting water loss (WL) during osmotic dehydration of apples in sugar beet molasses at different concentrations (40–80 °Bx) and temperatures (45–65C). Analyses of variance was used in order to find significant effects of temperature, dry matter content of solution and time on WL. All analyzed variables showed statistically significant influence on WL at α = 0.05 (F > Fα). The strongest impact on WL has dry matter content in molasses while the weakest has a temperature. High values of coefficient of determination, obtained for Peleg's constants k1 and k2, indicate that Peleg's model satisfactory fit experimental data. By defining the dependence of Peleg's constants on temperature and dry matter content, new mathematical model for WL was developed. High values of coefficient of determination (R2 = 0.933) and low standard deviation (SD = 0.043) show that new model describes well the experimental data. Practical Applications Osmotic dehydration is the method appropriated to reduce postharvest losses of fruits, and a common process for producing dried fruits, which can be directly consumed as snacks or used as an ingredient in cakes, pastries, yoghurts and many others food products. This study intends to investigate the effects of concentration, osmotic solution temperature and immersion duration on the kinetics of mass transfer. With Peleg's equation as initial model, we developed good and simplified mathematical model water loss (WL), during osmotic dehydration of apples in sugar beet molasses. With the model, the prediction of WL for apple cubes, under conditions stated above, could be very simple and fast.

Modeling of Mass Transfer during Osmotic Dehydration of Apple Using an Enhanced Lumped Model

In this study, an improved lumped model has been developed for transient one-dimensional mass transfer inside a solid material during osmotic dehydration using a polynomial approximation method. The proposed model was validated by experimental water loss and solid gain data obtained from osmotic dehydration of infinite slab and infinite cylindrical-shaped samples of apple in sucrose solution. Experiments were conducted at nine combinations of three solution concentrations (30%, 40%, and 50% w/w) and three temperatures (30°C, 40°C, and 50°C). The two-parameter model, developed by Azuara et al., was used to predict water loss and solid gain at equilibrium condition and moisture and sucrose diffusivities were estimated by fitting the experimental moisture loss and solid gain data to the Fick's second law of diffusion. The predicted values of average water loss and solid gain by polynomial approximation method fit approximately well to the experimental data and also to the predicted values by the exact analytical method. The values of mean relative errors for the polynomial approximation method with respect to the experimental data were estimated between 15.0 and 19.1%. Also, the related mean relative errors for exact analytical method were between 4.5 and 8.1%.

Application of Peleg model to study mass transfer during osmotic dehydration of apple in sugar beet molasses

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 (SG), during OD in 40-80% sugar beet molasses solutions, at 45, 55 and 65?C. High regression coefficients obtained for Peleg constants (R2>0.975) indicate good fit to the experimental data. The Peleg rate constant varied from 0.144 to 0.785 (g/g i.s.w.) and from 2.006 to 4.436 (g/g i.s.w.) for WL and SG, respectively. The Peleg capacity constant varied from 1.142 to 1.553 (h g/g i.s.w.) and from 8.254 to 11.930 (h g/g i.s.w.) for WL and SG, respectively. The equilibrium WL? and SG? were estimated using the Peleg model. In addition, the activation energy (Ea) for WL and SG was determined from the relationship between the Peleg rate constant and Arrhenius equation.

Osmotic dehydration of apples in sugar/salt solutions: Concentration profiles and effective diffusion coefficients

Apples ( Fuji variety) were treated in aqueous sucrose (50% w/w) and salt (NaCl, 10% w/w) solutions for 2, 4 and 8 h (27 °C). Concentration profiles were determined as a function of the distance, considering the unidirectional and normal diffusion to the exposed face of the immersed fruit. The density, water, sugar and salt contents were determined for each piece of apple. A mathematical model was fitted to the experimental data for the water, sucrose and salt contents. A numerical method of finite differences allowed for the calculation of the effective diffusion coefficients as a function of concentration, using the material coordinates to consider tissue shrinkage. The coefficients were obtained by simultaneously integrating the three differential equations (for water, sucrose and salt). The behavior of the apple cellular tissue was also studied using light microscopy techniques to obtain images of the osmotically treated pieces.

Effect of Temperature and Cultivar on Polyphenol Retention and Mass Transfer during Osmotic Dehydration of Apples

Several cultivars of apples (Malus domestica) were chosen for their variable concentrations and compositions in phenolic compounds. Cubed samples (1 cm3) were subjected to osmotic dehydration, and the effect of temperature was studied at 45 and 60 degrees C. Water loss, sucrose impregnation, and the evolution of some natural components of the product were followed to quantify mass transfer. Ascorbic acid and polyphenols were quantified by HPLC for several osmotic dehydration times and regardless of the quantity of impregnated sugar. Changes in antioxidant components differed as a function of the nature of molecules. Their concentrations decreased in line with temperature, and few differences were observed between cultivars. Processing at a lower temperature (45 degrees C) caused a total loss in ascorbic acid but allowed the retention of between 74 and 85% of initial polyphenols, depending on the cultivar. Cultivars containing highly polymerized procyanidins (such as Guillevic) experienced less loss. Hydroxycinnamic acids and monomeric catechins displayed the most marked changes. Leaching with water into the soaking solution was the principal mechanism retained to explain these losses.

Mass transfer during osmotic dehydration of apples

Osmotic dehydration processes are widely applied to obtain high quality intermediate moisture food. The study of dehydration kinetics and mass transfer mechanisms is very important for understanding and controlling the osmotic dehydration process. The internal changes and kinetics of both moisture change and mobility during osmotic dehydration of apples is reported. The effective diffusion coefficient of water was not constant during the dehydration treatment. Initially the effective diffusion coefficient calculated using a Fickian-based model was 2 ∗ 10 −10 m 2/s and increased to 5 ∗ 10 −10 m 2/s during treatment. Moreover, results showed the existence of an osmotic dehydration front that moves from the surface to the core of apple samples. It was not possible to explain the osmotic treatment process using only diffusion-based mechanisms. All layers of cells appear to be involved in the moisture transport process at the same time.

Assessment of Osmotic Process in Combination with Coating on Effective Diffusivities during Drying of Apple Slices

The effect of carboxymethyl cellulose (CMC) coating on the mass exchanges during the osmotic dehydration of apples and its effect on the quality of final product were studied. Coating semi-rings of apple with CMC solution (1%) was found to prevent solute uptake and to reduce salt diffusion coefficient from 4.35 × 10−10 m2/s to 2.86 × 10−10 m2/s. However, coating did not significantly affect the diffusivity of water. The effective diffusivity of salt and consequently solids gain were found to be depended on the concentration of CMC solution in the range of 0–1%. Increasing the concentration of CMC further from 1% had no effect on the mass exchanges during the osmotic process. Maximum performance ratio, defined as water loss/solids gain, and the lowest solids diffusion was observed for coated samples (with 1% CMC solution) treated with an osmotic solution containing glucose syrup (50%) and NaCl (2%).

Application of the Guggenheim, Anderson and De Boer model to correlate water activity and moisture content during osmotic dehydration of apples

Water activity and moisture content are the most valuable characteristics for assessing the stability of dried foods. The aim of this work was to evaluate if a desorption isotherm model could be used to describe the relationship between the water activity and moisture content in the product during osmotic dehydration. This model can lead to a better understanding of how water activity of a product can be reduced during osmotic dehydration. The Guggenheim, Anderson and De Boer (GAB) model was chosen because it has been proven to best fit the desorption and adsorption of foods over a large range of water activities. The studied material was apple pieces, and the osmotic medium with a water activity of 0.939 was prepared with sucrose. The osmotic dehydration process was studied by collecting moisture content and water activity data at different temperatures and times. The model was shown to fit well the experimental points at temperatures 25, 45 and 55 °C. At 65 °C, however, the model is satisfactory if a w is below 0.970 but not above. The effect of temperature can be expressed on the C-parameter of the GAB model.