Mass transfer phenomena during osmotic dehydration of apple II. Frozen plant tissue

In Part 1, mass transfer phenomena during osmotic dehydration of fresh apple tissue were qualitatively interpreted in terms of simultaneous osmotic and diffusive effects. This second part gives results obtained with frozen apple tissue, using the same experimental procedures with response-surface methodology and microscopic analysis. Results indicated that transfers were only diffusive and confirmed that high molecular weight solutes were the most effective in forming a dense solute barrier layer at the surface of the product, thus enhancing the dewatering effect during soaking treatment in the concentrated solution.     

Mass transfer during osmotic dehydration of pineapple rings

The effect of temperature (30, 40 and 50°C) and sucrose concentration (50, 60 and 70°Brix) on the osmotic dehydration of commercial size pineapple rings were studied, at an initial ratio of 1:4 fruit:sucrose solution. The rate of water loss in the fruit varied with both osmotic solution concentration and temperature. A proposed model based on Crank's equation was fitted to the experimental data.     

Mass transfer kinetics during osmotic dehydration of pomegranate arils

The mass transfer kinetics during osmotic dehydration of pomegranate arils in osmotic solution of sucrose was studied to increase palatability and shelf life of arils. The freezing of the whole pomegranate at -18 °C was carried out prior to osmotic dehydration to increase the permeability of the outer cellular layer of the arils. The osmotic solution concentrations used were 40, 50, 60°Bx, osmotic solution temperatures were 35, 45, 55 °C. The fruit to solution ratio was kept 1:4 (w/w) during all the experiments and the process duration varied from 0 to 240 min. Azuara model and Peleg model were the best fitted as compared to other models for water loss and solute gain of pomegranate arils, respectively. Generalized Exponential Model had an excellent fit for water loss ratio and solute gain ratio of pomegranate arils. Effective moisture diffusivity of water as well as solute was estimated using the analytical solution of Fick's law of diffusion. For above conditions of osmotic dehydration, average effective diffusivity of water loss and solute gain varied from 2.718 × 10(-10) to 5.124 × 10(-10) m(2)/s and 1.471 × 10(-10) to 5.147 × 10(-10) m(2)/s, respectively. The final product was successfully utilized in some nutritional formulations such as ice cream and bakery products.     

Modelling of mass transfer during osmotic dehydration of apple tissue pre-treated by pulsed electric field

The osmotic dehydration mechanism of apple sample pre-treated by pulsed electric field (PEF) was investigated over a range of 44.5-65 ° Brix sucrose concentrations. Apple disks treated by PEF field of 0.90 kV/cm during a constant time were immersed in sucrose solution at ambient temperature with 3:1 syrup to apple ratio (w/w). Increase of the initial solute concentration and the PEF treatment resulted in acceleration of the osmotic dehydration (OD). The PEF-treated samples had a higher water loss (WL) and higher solid gain (SG) than the untreated samples. The osmotic dehydration kinetics was studied on the basis of two approaches: Fick's unsteady state diffusion equation and a two-exponential kinetic model. The coefficients of effective diffusion of water and solute were calculated. Their values were higher for samples pre-treated electrically. The effect of PEF was more pronounced for the WL comparatively to the SG. The two-exponential kinetic model permits evaluating of both convective and diffusion stages of OD. The PEF pre-treatment accelerates the kinetics of water and solute transfer during convective and diffusion stages of OD.     

Mass transfer modelling of the osmotic dehydration of some fruits

An empirical model was developed to predict the water loss and solid gain during osmotic dehydration of apple, banana and kiwi fruit. The model is based on a first-order kinetic equation, in which the rate constant is a function of the main process variables (speed of agitation, solute concentration, size of fruit and process temperature). This model was applied to a wide range of experimental data on the osmotic dehydration of apple, banana and kiwi fruit, and its parameters were estimated using non-linear regression analysis. The results showed that all of the above process variables have a significant effect on the mass transfer phenomena during osmotic dehydration.     

Mass transfer during the osmotic dehydration of West Indian cherry

The main purpose of this work was to study water loss, solids gain, and weight and moisture reduction during the osmotic dehydration process of the West Indian cherry (Malpighia punicifolia). The diffusion coefficient of West Indian cherry was estimated by the inverse method using average moisture contents. Osmotic dehydration was examined for 12 h in a 65°Brix solution at temperature of 27 °C, without agitation, using a fruit:solution mass ratio of 1:4, 1:10, and 1:15. The kinetics and internal changes occurring during the osmotic dehydration of West Indian cherry are reported. The product’s drying kinetics was simulated using the diffusion model, and two optimization methods, Levenberg–Marquardt and Differential Evolution algorithm, were used to predict the diffusion coefficient. The results indicated that the two optimization methods performed similarly in estimating the diffusion coefficient adequately. The average calculated diffusion coefficient was 1.663 × 10^?10 m²s^?1, which is consistent with values reported in the literature.     

Comparative behaviour of cellulosic and starchy plant materials during osmotic dehydration

Osmotic dehydration studies on two cellulosic plant materials—Golden Delicious and Cox apple—and two starchy plant materials—banana and potato—showed that the amount and rate of water loss occurred in the following descending order: Golden Delicious > Cox > potato > banana. Temperature, concentration and immersion time of samples in the osmotic solution played a significant effect on amount and rate of water loss in all commodities in a descending order as follows: 55 > 40 > 32.2 °C; 0.70 > 0.60 > 0.50 > 0.40 g kg^?1; and 30 > 60 > 90 > 120 min, respectively. A corresponding uptake of solids from the osmotic solution occurred, the rate been greatest over the first 30 min, before declining significantly thereafter. The diffusion coefficients for water loss (D_{eff, w}) measured by the method of slopes on the water loss rate curves conducted at 32.2, 40 and 55 °C for 0.40, 0.50, 0.60 and 0.70 g kg^?1 sucrose concentration solutions were higher for cellulosic plant materials than starchy plant materials. Significant variations occurred in efficiency index (WL/SG) between cellulosic and starchy plant materials. Copyright © 2007 Society of Chemical Industry     

莴笋渗透脱水传质研究及参数优化

以失水率(WLR)和固形物增加率(SGR)为实验指标,采用二次回归正交旋转设计,选取葡萄糖溶液浓度(10%～40%)、氯化钠溶液浓度(2%～5%)、温度(35～65℃)、切片厚度(3～7mm)和渗透时间(60～150min)为影响因素,研究这5因素对莴笋渗透脱水指标的影响。使用SPSS软件拟合出了指标的回归方程,并利用方差分析研究了各因素对指标的影响程度。结果表明:除氯化钠溶液浓度外,其他4因素对失水率有极显著影响,而5种因素对固形物增加率有极显著作用。由Matlab软件优化的莴笋渗透脱水回归方程各参数为:葡萄糖浓度32.5%,氯化钠浓度2%,温度35℃,厚度5mm,渗透时间139min。     

Mass transfer kinetics of pulsed vacuum osmotic dehydration of guavas

The effects of vacuum pulse and solution concentration on mass transfer of osmotically dehydrated guava slices were studied. Kinetics of weight reduction (WR), water loss (WL), solid gain (SG) and water activity (a_w) were obtained using sucrose solutions at 40, 50 and 60 °Brix and vacuum pulse of 100 mbar for 0, 10 and 15 min at the process beginning. Higher solution concentrations and the vacuum pulse application caused an increase on WL of osmotically dehydrated guavas and reduced the samples water activity. The SG was reduced by the increase on osmotic solution concentration and favored by vacuum application. Two different models of kinetics diffusion were tested to obtain diffusivity and to compare the accuracy of these models. The effective diffusivity estimated by the hydrodynamic model well reproduced the effects of process variables on mass transfer kinetics and showed a better agreement to the experimental data than the diffusional model.     

Mass transfer during osmotic dehydration of pineapple: considering Fickian diffusion in cubical configuration

Osmotic dehydration kinetics of pineapple cubes (15×15×15 mm³) was studied over a range of concentration (40-70°B) and temperature (30-50°C) of osmotic solution. The effective diffusion coefficients for water and solute diffusion were determined, considering pineapple as cubical configuration, assuming osmotic dehydration to be governed by Fickian diffusion. The effective diffusion coefficients for water as well as solute were empirically correlated with concentration and temperature of osmotic solution. A high degree of correlation was observed between predicted and experimental values of the effective diffusion coefficients of water (R²=0.99) as well as solute (R²=0.96).     

Mass transfer kinetics during osmotic dehydration of bananas (Musa sapientum,shum.)

Osmotic dehydration is used widely to partially remove water from plant tissues by immersion in a hypertonic solution. In this work, the influence of temperature (25–55 °C), sugar concentration (30–60%) and salt concentration (0–10%) of the osmotic solution was investigated during osmotic dehydration of banana (Musa sapientum, shum.). Mass transfer kinetics were modelled according to Peleg’s equation. Kinetic parameters were evaluated using response surface methodology. Peleg’s equation showed to be suitable for modelling the water removal and solute uptake. Initial rate of water loss and water concentration at equilibrium were influenced by linear factors of the three independent variables. Initial rate of sucrose uptake and sucrose uptake at equilibrium were affected by all factors and interactions. Initial rate of salt uptake and salt concentration at equilibrium showed a positive correlation with temperature and NaCl concentration and a negative correlation with sucrose concentration.     

Mass transfer properties of osmotic solutions. I. Water activity and osmotic pressure

Abstract

In this review paper data on water activity, solute activity and osmotic pressure of”; binary and multi‐component osmotic solutions are provided. The Characteristics of the osmotic solutions are needed for the optimization of mass transfer during osmotic process, and for the improvement of final product quality. The vant Hoff equation and Gibbs Duhem theorem are commonly used to estimate osmotic pressure and solute activity. Water activities can be easily estimated through experimental determination of the freezing point depression. The possibilities of the group contribution models such as the Analytical Solution of Groups (ASOG) approach are also explored. The future needs especially in the case of multicomponent solutions consisting of electrolyte and non‐electrolyte mixtures are pointed out.     

Nonlinear thermodynamic approach to analyze long time osmotic dehydration of parenchymatic apple tissue

Osmotic dehydration experiments of Granny Smith apple were carried out in order to model the operation by using a nonlinear irreversible thermodynamic approach. Samples were immersed into 65% (w/w) sucrose aqueous solution at 30 °C during 180, 360, 480, 720, 1463, 1577, 1722, 3375, 4320, 7200, 8540, 10,270 min. Some physical-chemical parameters were measured in fresh, treated and reposed (24 h at 30 °C) samples. The results allow identifying three differentiated steps in the osmotic operation process. At the beginning of the treatment, the cells were turgid and the wall-membrane system stored high level of mechanical energy. In this step, the highest velocity of shrinkage occurred. In the second step, the main driving force was diffusional, with important concentration profiles in the tissue; in this step, the deformation of the tissue reached the maximum shrinkage level of approximately 60%. It produces an important structural change in the tissue removing the concentration profiles and changing the mechanism driving forces. Last step shows internal relaxation of the tissue, increasing the mechanical transport behaviours.     

Application of microwaves dielectric spectroscopy for controlling long time osmotic dehydration of parenchymatic apple tissue

Dielectric spectroscopy studies have been performed on fresh and osmotically dehydrated Granny Smith apples. The osmotic treatment consisted on immerse the samples into 65% (w/w) sucrose aqueous solution at 30 °C during different exposure times lasted from 3 h to 16 days. Some physical-chemical parameters were measured in fresh, treated and reposed (24 h at 30 °C) samples. Dielectric spectra were measured in the frequency range from 500 MHz to 20 GHz by an Agilent 85070E Open-ended Coaxial Probe connected to an Agilent E8362B Vector Network Analyzer in the fresh, treated and reposed samples. It has been demonstrated that the dielectric properties are a good tool to control the surface water activity by using the loss factor at relaxation frequency. This relation of dielectric properties with the water activity allows controlling the shrinkage level and determines the moment when the driving forces change from diffusional to mechanical behaviors. This value corresponds to 12.25 ± 0.16 and represents a practical control value to decide if the final dehydrated samples shrink or swell. Moreover, the quantity of adsorbed water was estimated by the subtraction between the overall moisture and the water content in liquid phase estimated by using dielectric loss factor at relaxation frequency.     

Mass transfer kinetics and regressional‐desirability optimisation during osmotic dehydration of pumpkin,kiwi and pear

Mass transfer kinetics and optimisation of osmotic dehydration (OD) of fruits and vegetables with diverse structures were studied. Different concentrations of sucrose (20–60 °Brix) and process times (0–24 h) were used. Magee’s model was appropriate for predicting water loss (WL), while Azuara’s model fitted well solids gain (SG) data and represented more accurately the evolution of the complete process close to equilibrium. Polynomial equations for each kinetic variable [WL, SG and weight reduction (WR) – for pumpkin, kiwi and pear] using multiple linear regression were fitted for a selected range of experimental data (30–240 min, 20–60 °Brix). A complete solution algorithm for desirability function was coded in Matlab^® 7.2 (Mathworks, Natick, MA, USA) with the aim to optimise osmotic dehydration process in terms of WL, SG and WR; optimal conditions were found for each fruit. Besides, an optimal common zone was identified for OD corresponding to process time from 114 to 240 min and sucrose concentration from 54 to 60 °Brix.     

Impact of mass transport on microstructure of Granny Smith apple parenchyma during osmotic dehydration

The chemical components of foods are organized in microscopic structures that can modify mass transfer. The study of material penetration in foods can be made using X‐ray microanalysis. In order to study the microstructural behaviour when fruit was osmotically dehydrated, a glucose molecule modified with chloral (1,2‐O‐2′,2′,2′‐trichloroethylidene‐α‐D ‐glucofuranose) was used as an osmotic standard with chlorine detectable by energy‐dispersive X‐ray analysis. Parenchyma of Granny Smith apple is a simple tissue, so it was chosen as reference. The results show that both the apoplastic and symplastic routes played an active role in mass transfer. The osmotic agent penetrated both the symplast and apoplast well into the depths of the fruit, although greater deterioration of cells was observed near the surface. Copyright © 2003 Society of Chemical Industry     

Mass transfer kinetics and mathematical modelling of the osmotic dehydration of orange‐fleshed honeydew melon in corn syrup and sucrose solutions

A simple mathematical model to predict dehydration and impregnation process during osmotic dehydration of orange‐fleshed honeydew in sucrose and corn syrup solutions was proposed. Results showed low dispersion and a good fitting capability for WL and SG kinetics. Diffusivity values for WL ranged from 0.96 × 10^?10 to 2.22 × 10^?10 and 1.04 × 10^?10 to 3.10 × 10^?10 m² s^?1 in corn syrup and sucrose solutions, respectively. For SG, the obtained range was 0.72 × 10^?10 to 2.35 × 10^?10 and 0.71 × 10^?10 to 2.46 × 10^?10 m² s^?1 in corn syrup and sucrose solutions, respectively. The half‐life of dehydration rates (t_1/2) was from 30.9 to 71.2 min and from 19.4 to 57.5 min in corn syrup and sucrose solutions, respectively. Diffusivities values obtained according to the proposed model were close to the ones observed from diffusive model; t_1/2 was a promising criterion for the process time definition.     

Review characterization of edible films formulated with sodium alginate and low-methoxyl pectin in osmotic dehydration applications

The aim of this work was to evaluate the behaviour of two edible films (sodium alginate and low-methoxyl pectin) under different osmotic conditions (solutions: sucrose, glucose syrup and maltodextrin; concentrations: 40 °Brix and 60 °Brix; temperature 40 °C and processing times: 0.5, 1 and 2 h). From the experimental water loss and solid uptake kinetics, effective diffusion coefficients and the dehydration performance ratio were obtained. The microstructural characteristics of the osmodehydrated films were also analysed using pear as a food matrix. The results showed that films osmodehydrated with maltodextrin and glucose syrup solutions presented higher dehydration performance ratio values than those osmodehydrated with sucrose. A reduction in the thicknesses of edible coatings was observed. The best formulation was sodium alginate 2% and calcium lactate 5% according to the microstructural analysis and structural integrity for at least up to 16 h of osmotic dehydration.