Ultrasound-Assisted Osmotic Treatment of Model Food Impregnated with Pomegranate Peel Phenolic Compounds: Mass Transfer,Texture, and Phenolic Evaluations

Food impregnation with nutraceutical components due to the health beneficial property is of great importance for food processing industry. In this study, osmotic dehydration was used to impregnate model food with phenolics extracted from pomegranate peel. Intermittent acoustic treatment was applied to enhance mass transfer. This process was carried out at three sucrose concentrations of 40, 50, and 60% and two levels of power ultrasound, 50 and 100% in an experimental setup, which was equipped with a pump circulating osmotic solution frequently. Results showed that increase in sucrose concentration resulted in an increase in the amounts of water loss and solutes gain. Additionally, application of higher power ultrasound led to higher values of water loss and solid gain. Mass transfer modeling using Azuara model predicts water loss and solid gain values at equilibrium. Results revealed the good correlation of experimental values with the model (due to the R² values greater than 0.94). The microstructure of samples was investigated using scanning electron microscopy (SEM). Images revealed pores and cavities made by ultrasound waves as the result of spongy effects. Texture profile analysis (TPA) was applied for the determination of hardness, springiness, and gumminess of the samples. Results also showed significant effects of the sucrose concentration and ultrasound power on textural properties. Measurements of total phenolic content and antiradical activity, which were carried out by a colorimetric method and antiradical scavenging assay, EC50, respectively indicated that osmotic dehydration is a possible way for uptaking phenolic compounds of pomegranate peel presented in osmotic solution into food matrices.     

Mass transfer modelling in ultrasound assisted osmotic dehydration of kiwi fruit

In this study, the effect of ultrasonic pre-treatment on osmotic dehydration of kiwi slices was investigated. Kiwi fruit slices were subjected to ultrasonic pre-treatment in a sonication water bath at a frequency of 25 kHz for 20 min. Osmotic dehydration of ultrasonic pre-treated samples were conducted for a period of 300 min in 60 Brix sucrose solution. The kinetics of moisture loss and solute gain during osmotic dehydration were predicted by fitting the experimental data with Azuara's model and Weibull's model. The effects of ultrasound application on water loss, sugar gain, effective moisture diffusivity and solute diffusivity of the samples were analysed. The osmotic dehydration process showed a rapid initial water loss followed by a progressive decrease in the rates in the later stages. From the Azuara's model, the predicted equilibrium water loss value for ultrasound pre-treated sample was 58.4% (wb) at 60°C that was nearly 16% higher than the samples treated under atmospheric conditions. Fitting of Weibull model showed that the ultrasound pre-treated and untreated samples had shape parameter (β_w) ranging between 0.570–0.616 and 0.677–0.723 respectively. The lower values of shape parameter indicated that sonication caused accelerated water loss resulting faster dehydration rate. Results indicated that the effective moisture diffusivity and solute diffusivity was enhanced in ultrasonic pre-treated samples. The effective moisture diffusivity during osmotic dehydration of ultrasonic pre-treated samples was ranged between 5.460×10⁻¹⁰–7.300×10⁻¹⁰ m²/s and solute diffusivity was varied between 2.925×10⁻¹⁰–3.511×10⁻¹⁰ m²/s within the temperature range 25–60 °C. The enhanced moisture and solute diffusivity in ultrasound pre-treated kiwi slices was due to cell disruption and formation of microscopic channels.     

Effect of Power Ultrasound and Pulsed Vacuum Treatments on the Dehydration Kinetics,Distribution, and Status of Water in Osmotically Dehydrated Strawberry: a Combined NMR and DSC Study

The effect of power ultrasound and pulsed vacuum (PV) treatments on the dehydration kinetics and the status of water during osmotic dehydration of strawberries was investigated. Low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) were used to determine the spatial distribution and status of water within the cellular and intercellular spaces. Differential scanning calorimetry (DSC) was used to determine the freezing point depression and the amount of frozen water. Osmotic treatment was performed by immersing the samples in 25 and 50 % (w/w) sucrose solutions at 40 °C for 3 h. Water loss and solid gain of strawberry samples were measured and the data were fitted by Peleg’s model. The Peleg’s model fitted the experimental water loss and solid gain kinetics data well (R ²?>?0.98). At a given sucrose concentration, the highest water loss and the highest decrease in firmness occurred while using ultrasound treatment, while the highest solid gain and the highest firmness values were achieved by pulsed vacuum treatment. LF-NMR signals were able to quantify the effect of water-osmotic solute exchange on the cell compartments (vacuole, cytoplasm plus intercellular space, and cell wall). The LF-NMR data showed that the relative space occupied by the vacuole decreased and the relative space occupied by the cytoplasm and intercellular space were increased due to these osmotic treatments. MRI results indicated that a bright “water strip” appeared in the periphery of all the osmotically dehydrated samples. DSC results showed that the decrease in water content and the increase in the osmotic solutes depressed the initial freezing point and the freezable water content in osmotically dehydrated strawberry.     

Osmotic Dehydration of Nectarines: Influence of the Operating Conditions and Determination of the Effective Diffusion Coefficients

The aim of the present work is to study the kinetics of osmotic dehydration of Caldesi nectarines (Prunus persica var. nectarina) evaluating the effect of osmotic solution concentration, type of solute, temperature, fruit/solute ratio and process time on moisture content, water loss, soluble solids content and solids gain. The process analysis was carried out experimentally and numerically through the mathematical modelling of mass transfer. Hypertonic solutions of glucose syrup and sorbitol (40 and 60 % w/w) were used for dehydration, during 2 h of process at temperatures of 25 and 40 °C, with fruit/osmotic agent ratio of 1:4 and 1:10. Water loss and solids gain showed significant differences depending on the type and concentration of the osmotic agent, process time and fruit/solution ratio. The concentration interacted significantly with all variables; in addition, there was an interaction between the type of osmotic agent and the relationship between fruit and the osmotic agent. The effective diffusion coefficients were obtained from the analytical solution of Fick’s second law applied to flat-plate geometry and by solving the mass transfer microscopic balances by finite element method, taking into account the real geometry of the nectarine pieces. The values obtained from Fick’s law varied between 1.27?×?10^?10 and 1.37?×?10^?08?m²?s^?1 for water and from 1.14?×?10^?10 to 1.08?×?10^?08?m²?s^?1 for soluble solids, while the values calculated by finite elements method ranges were between 0.70?×?10^?09 and 4.80?×?10^?09?m²?s^?1 for water and between 0.26?×?10^?09 and 1.70?×?10^?09?m²?s^?1 for soluble solids. The diffusion coefficients values obtained from the numerical solution are consistent with those published in literature.     

Osmotic dehydration process for low temperature blanched pumpkin

This study investigated the influence of stepwise blanching over the kinetics of osmotic dehydration process and over the physical characteristics of pumpkin (Cucurbita moschata). The 2³ factorial design and response surface methodology was used to optimize the blanching process. The independent variables for blanching were temperature, blanching time and holding time. These independent variables showed different effects on the two studied answers: texture and color. The kinetics of osmotic dehydration were investigated using 50% and 65% sucrose solutions, using samples previously blanched by both stepwise and conventional means. The diffusivity values for the water and sucrose were similar for the two components, showing greater gains of solute than loss of water in many samples. Blanching affected the color of the pumpkin, whereas osmotic dehydration did not change it significantly. The impregnation process maintained or even increased the tissue firmness when compared to the blanched samples.     

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.     

超声波强化紫薯渗透脱水工艺

分别以蔗糖质量分数、渗透温度、渗透时间和超声波功率为单因素,研究其对紫薯超声波渗透脱水的脱水率和固形物增加率的影响。以各因素为自变量,以脱水率和固形物增加率为因变量,对紫薯渗透脱水进行响应面工艺研究,得出最优工艺参数。结果表明：影响脱水率和固形物增加率的主次顺序均为渗透时间＞渗透温度＞糖液质量分数＞超声波功率;响应面优化最优工艺参数为糖液质量分数56.29%、渗透液温度65℃、渗透时间2.46h、超声波功率142.33W。结合实际操作,响应面优化的最优工艺调整为糖液质量分数56%、渗透液温度65℃、渗透时间2.5h、超声波功率140W,经验证,此条件下脱水率为40.79%,固形物增加率为8.33%。     

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 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.     

Rehydration kinetics and soluble solids lixiviation of candied mango fruit as affected by sucrose concentration

Rehydration behaviour of candied mango samples was studied. The influence of candy process conditions and rehydrating medium on the rehydration kinetics was studied. In this sense, water gain, solute loss and compositional changes in the fruit liquid phase were fitted using Peleg’s model. Mango cubes were candied using two osmotic dehydration steps (applying vacuum impregnation in the first) plus air drying at 35 °C till 80% or 90% soluble solids was obtained. Four combinations of sucrose solutions (^°Bx) was used in the osmotic steps: 25–65, 45–45, 45–65 and 65–65. Rehydration process were carried out at 10 °C for 8 h on sucrose solutions (0, 10, 20 and 30^°Bx). Candied samples using 45^°Bx sucrose in the two osmotic steps showed the highest solute retention at equilibrium. A higher drying level of candied fruit also implied the greatest solute retention.     

Enrichment of Banana with <Emphasis Type="Italic">Lactobacillus rhamnosus</Emphasis> Using Double Emulsion and Osmotic Dehydration

The aim of this study was to use the process of osmotic dehydration to enrich banana slices with Lactobacillus rhamnosus encapsulated in a double emulsion. The effect of a pulsed vacuum and the concentration of the osmotic solution on the impregnation of the microorganism and on mass transfer during osmotic dehydration of the fruit were assessed. The kinetics of the water loss (WL), solid gain (SG) and water activity (a_w) were obtained using an aqueous solution with 40, 50 and 60% sucrose with emulsion and a vacuum pulse of 50 mbar for 10 and 20 min at the beginning of the osmotic process. The high concentrations of sucrose in the osmotic solution, combined with the application of a pulsed vacuum, produced an increase in the rates of WL and SG of the osmodehydrated banana, as well as a reduction of its a_w. L. rhamnosus survived at levels above 10⁷ CFU/g in the hypertonic solution and in the osmodehydrated bananas. Scanning electron microscopy (SEM) showed that the encapsulated probiotic adheres to the banana’s surface, which demonstrates that double emulsions can be used to impregnate probiotics in vegetal tissues.     

Study of the Pseudo-equilibrium During Osmotic Dehydration of Apples and Its Effect on the Estimation of Water and Sucrose Effective Diffusivity Coefficients

The study of the equilibrium is needed not only for modeling of the osmotic process as a unit operation but also for a better understanding of the mass transfer mechanisms involved in this kind of systems. A true equilibrium state usually takes very long time to achieve; therefore, a pseudo-equilibrium state is often employed. Experimental pseudo-equilibrium states for water loss and solid gain during the osmotic dehydration of apple slices (5?×?50?×?50?mm³) at different osmotic syrup concentrations (30%, 40%, 50%, and 60% (w/w) of sucrose) were evaluated. Four empirical mathematical methods (Slopes, Azuara, Zugarramurdi and Lupín, and Equal concentration) were used in order to calculate the pseudo-equilibrium values obtained and then to compare them against to the experimental ones. Additionally, the effective diffusion coefficients for water and sucrose were calculated by using those pseudo-equilibrium values. Experimental pseudo-equilibrium values increased with concentration of the osmotic syrup, ranged between 24% and 56% for water loss and 11% and 28% for solid gain; the predicted pseudo-equilibrium values followed the same trend. The decreasing order of accuracy for pseudo-equilibrium values and effective diffusion coefficients, among the methodologies evaluated, was Equal concentration method > Azuara method > Slopes method > Zugarramurdi and Lupín method. Although the Equal concentration method has no theoretical accuracy, it is independent of the kinetic data presenting a higher advantage over the other three mathematical methods evaluated.     

Comparison of sucrose and fructo-oligosaccharides as osmotic agents in apple

Fructo-oligosaccharides and sucrose were compared as osmotic agents in the osmotic dehydration of apple cv. Idared. Dehydration process of apple cubes (10  10  10 mm) was performed to determine the weight reduction (WR), moisture content (MC), water loss (WL) and solid gain (SG) over a range of osmotic solutions (40–60% w/v), temperature (40–60 °C) and processing time (20–40 min) The effective diffusion coefficient of water and solute was calculated assuming the processes to be governed by Fick's unsteady state diffusion. The effective diffusion coefficients were found to be of the order of 10^− 9 m² s^− 1 and were effected by the type of solute significantly. The WR, MC, WL and SG were predicted as weighted linear combinations of temperature, concentration of solute and time of OD.

Industrial relevance

The use of fructo-oligosaccharides (FOS) in different fruit based products is an efficient way to enrich human diet with functional component, because of the well-known health benefits of FOS. The osmotic behaviour of fructo-oligosaccharides were studied and compared to the conventional used sucrose. In view of the changes of different osmotics regarding to unit parameters of osmotic dehydration the results give possibility to industrial technology planning of products containing FOS, which are available for consumption in every season of the year and are favourable also in processed form e.g. muesli, dairy products.     

Optimisation of osmotic dehydration of carrot cubes in sucrose-salt solutions using response surface methodology

Osmotic dehydration of carrot cubes in ternary solution of water, sucrose and sodium chloride at different solution concentrations, temperatures and process durations were analysed for water loss and solute gain during osmotic dehydration. The osmotically pre-treated carrot cubes were further dehydrated in a cabinet dryer at 65 °C and were then rehydrated in water at ambient temperature of water for 10–12 h and were analysed for rehydration ratio, shrinkage and overall acceptability after rehydration. The process was optimised for maximum water loss, rehydration ratio and overall acceptability of the rehydrated product, and for minimum solute gain and shrinkage of rehydrated product by response surface methodology. The optimum conditions of various process parameters are 50°B+10% w/v aqueous sodium chloride concentration, 46.5 °C solution temperature and 180 min process duration.     

Effect of pulsed-vacuum and ohmic heating on the osmodehydration kinetics, physical properties and microstructure of apples (cv. Granny Smith)

The influence of pulsed vacuum (PVOD) and ohmic heating (OH) on the osmotic dehydration (OD) kinetics and structure of apples was evaluated. Apple cubes (1 cm³) were immersed in a 65 ºBrix sucrose solution at 30, 40 and 50 °C for 300 min. The PVOD treatment was conducted at 5 kPa for 5 min, and the OH treatment was conducted at 100 V (electric field of 13 V/cm). The water loss, solid gain, a_w, color and firmness were measured, and the microstructure was analyzed using electronic microscopy. The largest water loss was observed with the OD/OH treatment at 50 °C. The greatest amount of solute uptake and smallest firmness loss were obtained with the PVOD/OH treatment at 50 °C. Color differences were associated with the loss of clarity and corresponded to the transparency gain. OH treatments led to changes in the microstructure, cell walls and tissues of the apples due to the electroporation effect, which explained the increase of mass transference.

Industrial relevance

The aim of this research was to determine the response of apple samples to osmotic dehydration using combined treatments of pulsed vacuum and ohmic heating. Two different technologies, vacuum and ohmic heating at mild temperatures, were used to determine and observe the mass transfer kinetics and microstructure of osmodehydrated apples. In several ohmic heating treatments, the time reduction reached 50% as compared to conventional heating. The increases of temperature, vacuum application and electroporation effect promoted the gain of osmotic solution into the tissue pores, thus reaching equilibrium in the sample with less water loss. Among the investigated conditions, the PVOD/OH treatment at mild temperatures was the best minimal processing method to preserve the fresh-like properties of the apples.     

Developments in osmotic dehydration technique for the preservation of fruits and vegetables

In recent years much attention has been focused on maintaining the freshness of fruits and vegetables by immersion of cellular materials containing water in an osmotic solution. It results in the development of intermediate moisture products having lower water activity, which is imparted by solute gain and water loss. During the process, chemical, physical and biological activities, which deteriorate the foods, are lowered considerably; hence extends the shelf life of food products. In this process moisture is withdrawn from the product at ambient temperature by diffusion, so phase change has been avoided. Besides, it helps to improve the nutritional and sensory attributes of food products and is less energy intensive process as compared to other drying techniques. Osmotic dehydration is influenced by various factors such as osmotic agent, time and temperature, solute concentration, solution to sample ratio, agitation and geometry of the materials. Recently, osmotic dehydration has been combined with several other methods namely, pulsed high electric field, high hydrostatic pressure, ultrasound, centrifugal force, vacuum and gamma irradiation. These techniques have been employed during or after osmotic treatment to enhance osmotic dehydration performance by increasing the cell membrane permeability and mass transfer rate. These combined operations reduce the drying time, minimizing further energy costs. In this study, various segments of osmotic dehydration techniques and its application in food processing as well as recent advances in osmotic dehydration have been reviewed.Industrial relevanceThe osmotic dehydration technique is gaining popularity as a mean of obtaining minimally processed food. This review paper deals with the kinetics and mechanisms of osmotic dehydration technique for the preservation of fruits and vegetables. The various factors effecting osmotic mass transfer rate in food have been reviewed. In this paper, the combined effect of osmotic dehydration and several other innovative techniques (pulsed high electric field, high hydrostatic pressure, ultrasound, centrifugal force, vacuum and gamma irradiation) on the quality and shelf life of fruits and vegetables have been reviewed. These techniques have been employed during or after osmotic treatment to enhance osmotic dehydration performance by increasing the cell membrane permeability. These combined operations reduce the drying time, minimizing further energy costs as well as improving the quality of fruits and vegetables during storage.     

OPTIMIZATION OF OSMOTIC DEHYDRATION PROCESS OF CARROT CUBES IN SUCROSE SOLUTION

ABSTRACT

For optimization of the osmotic dehydration process of carrot cubes in sucrose solution by response surface methodology (RSM), the experiments were conducted according to face‐centered central composite design. The independent process variables for the osmotic dehydration process were osmotic solution concentrations (45–55°Brix), temperature (35–55C) and process durations (120–240 min). Statistical analysis of results showed that all the process variables had a significant effect on all the responses at 5% level of significance (P < 0.05). The osmotic dehydration process was optimized by RSM for maximum water loss, rehydration ratio, retention of color, sensory score and minimum solute gain. The optimum process conditions were 52.5°Brix sucrose syrup concentration, 49C osmotic solution temperature and 150‐min process duration.

PRACTICAL APPLICATIONS

The process of osmotic dehydration can be used for the preparation of shelf‐stable products for the purpose of use during off‐season. The quality of preosmosed carrots is much superior to the product dehydrated with the convectional method of convective dehydration. The osmotically dehydrated carrots can be used for cooking as vegetables after rehydration or can be added directly into soups, stews or casseroles before cooking. If the product is blanched before osmotic dehydration, the process can be used successfully for the preparation of carrot candy.     

Osmotic Dehydration Kinetics of Pomegranate Seeds Using Date Juice as an Immersion Solution Base

Pomegranate seeds were osmodehydrated using date juice added with sucrose (final °Brix, 55) as immersion solution. The kinetics of osmotic dehydration showed that the most significant changes of mass transfer took place during the first 20 min of the process, regardless of date juice varieties. During this time, seed water loss and solid gain were estimated to be ∼39% and ∼6%, respectively. After 20 min of the process, the percentage of water loss and solid gain varied slightly and ranged on average close to ∼40% and ∼9%, respectively. During osmotic dehydration, there was a leaching of natural solutes from seeds into the solution, which is quantitatively not negligible, and might have an important impact on the sensorial and nutritional value of seeds and date juices. Both scanning electron microscopy and texture (compression) analysis revealed that osmotic dehydration process induced modifications of seed texture and cell structure. Sucrose was found to be the essential element which influences the texture of seed and the viscosity of date juice. Additionally, natural sugar present in date juice permits substituting 35% of the total quantity of sucrose added to the osmotic solution.     

莴笋渗透脱水有效扩散系数研究

以葡萄糖溶液浓度(10%～40%)和温度(35～65℃)为影响因素,研究了莴笋渗透脱水的动力学过程。分别使用Azuara模型和Fick第二扩散定律计算出了平衡时刻的失水率、固形物增加率以及相应的水分和固形物有效扩散系数。设计了均匀实验,通过曲面拟合的方法得到了水分、固形物有效扩散系数与因素的回归方程。结果表明:失水率随着葡萄糖溶液浓度增加而增大,但随着温度的升高而降低;固形物增加率随着溶液浓度和温度的增加而增加。Azuara模型可用来预测失水率和固形物增加率,通过曲面拟合得到的有效扩散系数回归方程拟合性较高。有效扩散系数反映了失水率和固形物增加率达到平衡时刻的快慢程度。