Modeling and Optimization of Microwave Osmotic Dehydration of Apple Cylinders Under Continuous-Flow Spray Mode Processing Conditions

The objective of this study was to model and optimize the mass transfer behavior during microwave osmotic dehydration of apple cylinders under continuous-flow spray mode processing conditions. Data needed for the model development and optimization were obtained using a central composite rotatable experimental design involving sucrose concentration (33.3–66.8°B), temperature (33.3–66.8 °C), flow rate (2,120–3,480 ml/min), and contact times (5–55 min); and the response variables were moisture loss, solids gain, and weight loss. Mass transfer kinetics was evaluated based on the empirical Azuara model and the conventional diffusion model. Diffusivities of both moisture loss (D _m) and solids gain (D _s) obtained from the diffusion model were related to sucrose concentration, temperature, and flow rate. Optimization was evaluated using a desirability function model which could be used with several imposed constraints. The optimum conditions obtained depended on the imposed constraints. A set of constraints involving maximizing moisture loss and weight reduction while keeping the solids gain below 3.5% gave the following optimal conditions: a 30-min osmotic treatment at 65°B, 60 °C, and 2,800 ml/min flow rate yielding a moisture loss of 40.9%, weight reduction of 37.7%, with a solids gain of 3.32%.     

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.     

Kinetics Modeling of Mass Transfer Using Peleg’s Equation During Osmotic Dehydration of Seedless Guava (<Emphasis Type="Italic">Psidium guajava</Emphasis> L.): Effect of Process Parameters

Peleg’s equation was used to study the effect of process parameters on kinetics of mass transfer in terms of solids gain and water loss during osmotic dehydration using 30–50% (w/w) sucrose solution at 30, 40 and 50 °C. The experimental data were successfully fitted employing Peleg’s equation with the coefficient of determination (R ²) higher than 0.88, the root mean square error, and the mean relative percentage deviation modulus (E) of less than 0.003% and 6.40% for all treatments, respectively. In all cases, initial mass transfer rate parameter (K ₁) decreased significantly (p < 0.05) as the solution concentration and solution temperature increased suggesting a corresponding increase in the initial mass transfer rate. Initial mass transfer rate followed an Arrhenius relationship which showed that solids gain had the highest temperature sensitivity (E _a = 21.93–33.84 kJ mol⁻¹) during osmotic dehydration. Equilibrium mass transfer parameter (K ₂) decreased significantly (p < 0.05) as solution concentration increased demonstrating that the equilibrium solid and water contents increased with increase in solution concentration. The equilibrium solid and water contents were also estimated adequately using Peleg’s equation (R ² > 0.78). The results of this work allow estimating the kinetics of mass transfer during osmotic dehydration in order to obtain products with determined solid and water contents.     

Acceleration of mass transfer rates in osmotic dehydration of elephant foot yam (Amorphophallus paeoniifolius) applying pulsed-microwave-vacuum

The elephant foot yam slices were processed with combined pulsed-microwave-vacuum osmotic drying. Osmotic dehydration at ambient (28 °C and 45% RH) was carried out using different levels of sucrose concentration (30, 40, 50 and 60% w/w), salt concentration (5, 7.5, 10 and 12.5% w/w) and dehydration time (10, 20, 30, 50, 70, 90 and 120 min). During the osmotic dehydration, pulsed microwave vacuum (15 kPa pressure, 1 W/g power density and 1.853 pulsating ratio) was maintained for 2 min over the sample and solution to enhance the mass transfer. For this purpose, the osmotic dehydration experiments were conducted in the microwave-vacuum cavity. Azuara model predicted the moisture loss and solid gain by elephant foot yam slices during osmosis. It was observed that both the moisture loss and the solid gain increased with increasing concentration of the osmotic solution. The optimum conditions found in the process were 40% w/w sucrose concentration, 6% w/w salt concentration and 70 min osmotic dehydration time, resulting in to 42.80% moisture loss (initial weight) and 14.65% solid gain (initial weight). Further, samples were dried using microwave vacuum dryer up to moisture content of 5–6% d.b. by varying microwave power density (2, 4, 6 and 8 W/g) and pulsating ratio (1.312, 1.625, 1.983 and 2.250). Page model was fitted to the data to study the microwave vacuum drying kinetics. The microwave vacuum drying at 1.625 pulsating ratio with microwave power density 4 W/g yielded a product with the highest overall acceptability score. Guggenheim, Anderson and deBoer (GAB) model was used in the study of the sorption behavior of dehydrated elephant foot yam and shelf life prediction.Industrial relevanceThe production of elephant foot yam in India and South East Asia is comparatively higher than other vegetables. Although, it is nutritious product and good source of energy, food industries are not interested to process elephant foot yam using a time consuming traditional osmotic dehydration process followed by hot air drying. Therefore, present research work was undertaken from industry suggestion to develop accelerated osmotic dehydration process for elephant foot yam using novel pulsed-microwave-vacuum combination followed by finish drying by microwave-vacuum. This research has been carried out to decrease industrial processing time, energy consumption and improving quality of the product. Industry will start adopting this new hybrid process of drying elephant foot yam on large scale.     

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.     

Response surface optimisation of osmotic dehydration of Chinese ginger (Zingiber officinale Roscoe) slices

Response surface methodology (RSM) of Box–Behnken design with 27 experimental runs and the desirability function method were used in the osmotic dehydration process of Chinese ginger (Zingiber officinale Roscoe) slices in ternary solution of water, sucrose and sodium chloride for maximising water loss (WL), rehydration ratio (RR) and total phenolic content (TPC) and minimising solute gain (SG) and hunter colour change (HCC) of dehydrated product. The results indicated that the optimum operating conditions were found to be process duration of 102 min, solution temperature of 30 °C, solution concentration of 50 Brix sucrose + 7.31% sodium chloride and solution to food ratio of 8:1 (w/w). Under this condition, the WL, SG and TPC were 58.8% (wb), 12.56% (wb) and 1.46% (db), while its RR and HCC were 1.59 and 6.55, respectively. The immersion time was the most significant variable for WL, HCC, SG and RR, and for TPC it was temperature (P < 0.05).     

Blanching of Strawberries by Ohmic Heating: Effects on the Kinetics of Mass Transfer during Osmotic Dehydration

The effect of blanching by ohmic heating (OH) on the kinetics of osmotic dehydration of strawberries was studied. Ohmic heating parameters obtained at two temperatures (65 and 85 °C). The osmotic dehydration (OD) parameters are the temperature (26 and 37 °C) and the sucrose in osmotic solution (30–70 °B). An approximate solution of Fick’s law for unsteady state mass transfer in spherical configuration has been used to calculate the effective diffusion coefficients of water and sucrose. Results show that ohmic heating increases drastically the mass transfer and the effective diffusion rates. After 4 h of OD (without OH) in a sucrose solution (at 37 °C and 70 °B), the dry matter of the untreated strawberry halves was 20.3%; while it reached 68% when OD was combined with blanching by OH at 85 °C for 3-min. Ohmic blanching permits the effective damage of cells by combination of electrical and thermal effects. That result has an important enhancement of water and sugar transfers during osmotic dehydration of strawberries.     

Image analysis of osmotically dehydrated fruits: melons dehydration in a ternary system

Osmotic dehydration represents a technological alternative to reduce post-harvest losses of fruits. In this work, the osmotic dehydration of a ternary system (water/sugar/salt) was investigated for melon (Curcumis melo L.) dehydration using image analysis. Three kinds of sugars were used to formulate the osmotic solutions: sucrose, glucose and manitol. The process of osmotic dehydration was studied and the effects of the ternary osmotic system on the fruit shrinkage were investigated using image analysis technique. The experimental study allowed estimating the process parameters of the osmotic dehydration. The results showed the advantage of using high sugar and salt concentrations for the osmotic solution, mild temperatures, and the use of the osmotic treatment to reduce the total processing time to dry the fruit. Image analysis enabled to show how far the solid penetrates inside the fruit and to estimate the shrinkage factor of the fruit during the osmotic dehydration.     

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.     

Effects of chitosan coating on mass transfer during osmotic dehydration of papaya

The aim of this work was to evaluate the influence of chitosan coatings in the osmotic dehydration of scalded cut papaya var. Red Maradol in two ripening stages (green and ripped). Papaya cubic cuts (1 cm³) were divided into three groups depending on the treatments: without chitosan coatings; with chitosan coatings at 1% (w/v) in lactic acid 1% (v/v) and Tween 80 at 0.1% (v/v); and with chitosan coatings at 1% (w/v) in lactic acid 1% (v/v), Tween 80 at 0.1% (v/v) and oleic acid at 2% (v/v). The study of dehydration kinetics and mass transfer was carried out with osmotic solution of sucrose (40°Brix) in a ratio fruit/solution of 1:60, and weight reduction, water loss and solids gain were measured. Chitosan coatings improved the efficiency of osmotic dehydration process in both ripening stages, increasing the water loss and decreasing the solids gain.     

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.     

OSMOTIC DEHYDRATION OF STRAWBERRIES IN A BATCH RECIRCULATION SYSTEM

Physical and chemical characteristics of two cultivars of strawberries during osmotic dehydration in sucrose and glucose solutions were investigated. Temperature was found to have a significant effect on the water and sugars (glucose, fructose and sucrose) exchange between strawberry and the osmotic solution. Mass transfer was found not to be significantly different between cultivars. Glucose gain was found to be higher than sucrose for the strawberries osmotically dehydrated in glucose and sucrose solutions at the same mole fraction, respectively. Sugars other than the osmotic sugar were found to decrease in concentration during the osmotic process. The combination of 63% sucrose solution with 25C process temperature for 2 h was able to remove more than 40% of moisture and load less than 0.1% of sucrose in the strawberries.     

COMPOSITIONAL CHANGES OF STRAWBERRY DUE TO DEHYDRATION, COLD STORAGE AND FREEZING–THAWING PROCESSES

Strawberry is an excellent source of food ingredients, although compositional changes might occur in improperly controlled processing, affecting product quality. In this article, changes in sugar composition (glucose, fructose and sucrose), citric acid, water and total soluble content, as induced by partial dehydration and freezing–thawing processes, were analyzed in strawberries (var. Camarosa). Osmotic dehydration (OD) with 65 °Brix sucrose solution, air drying (AD) at 45C, or combined treatments (OD–AD) were applied to reduce strawberries’ water content to 70–85%. Fresh and dehydrated samples were frozen (?40C, 24 h) and stored (?18C, 30 and 180 days). All samples processed by OD and OD–AD showed a significant sugar gain, and depending on the dehydration treatment, total or partial sucrose hydrolysis was observed. Dehydration treatments caused small losses of citric acid. During the freezing–thawing process, drip loss and enzymatic action also cause changes in sugar concentration, especially in OD‐treated samples.     

Optimization of osmotic dehydration of tomatoes in a ternary system followed by air-drying

Osmotic dehydration and air drying technology represent a technique that can reduce post-harvest loss of fruits and vegetables. In this work the influence of osmotic solution composition (water/sugar/salt) and temperature on the osmotic dehydration of tomatoes (Lycopersicum esculentum) were examined. Tomatoes with and without skin were studied. The process of osmotic dehydration followed by air-drying was studied and modeled, so it could be optimized aiming the reduction of total processing time. The results showed the advantage of two different processes for the tomatoes with skin and without skin. Tomatoes without skin are processed faster using air-drying without submitting the fruit to osmotic dehydration. Whereas, the tomatoes with skin dry faster when submitted to an osmotic solution consisting of 35% of sucrose and 5% of salt at 60 °C prior to air-drying.     

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.     

Artificial neural network modeling of mass transfer during osmotic dehydration of kaffir lime peel

Mass transfer of kaffir lime peel during osmotic dehydration was investigated in this paper. Processing factors were solute concentrations, process temperatures, and immersion time. The results showed that increasing solute concentration and process temperature resulted in a higher reduction in moisture contents of kaffir lime peel and increase in water loss and solid gain rates. Analysis of variance showed significant effects (P < 0.05) of all processing factors except process temperatures for water loss. Multilayer feedforward neural network (MFNN) was proposed to predict percentages of water loss and solid gain of kaffir lime peel during osmotic dehydration based on three processing factors as inputs. The best network with the lowest average mean squared error (MSE) of 0.0066 and the highest average regression coefficient (r²) of 0.9725 from normalized training and validating data sets was composed of one hidden layer with five hidden neurons and used Levenberg–Marquardt algorithm as a training algorithm. A simulation test showed good generalization of the successfully trained MFNN model with the average MSE of 6.5813 and 5.9340, and average r² of 0.9745 and 0.9632, respectively, for water loss and solid gain. Compared with multiple linear regression models, MFNN was found to be more suitable for predicting water loss and solid gain during the OD process of kaffir lime peel.     

Optimisation of vacuum pulse osmotic dehydration of blanched pumpkin

Pulsed vacuum osmotic dehydration (PVOD) is an efficient process for obtaining semi‐dehydrated food. The effects of temperature (30–50°C), solute concentration (NaCl 0–15 kg per 100 kg solution, sucrose, 15–35 kg per 100 kg solution) and vacuum pulse application (50–150 mbar and 5–15 min) on water loss (WL), solid gain (SG), water activity (a_w) and total colour difference (?E) of previously blanched pumpkin slices were assessed through Plackett–Burman experimental design. Temperature was not statistically significant in the process. Later, with the aid of a central composite design (CCD), it was found that concentration of sucrose and NaCl was influent on the WL, SG, a_w and ?E, and the pressure and time of application of vacuum were influent on WL and SG. The optimal conditions of process were stabilised with the desirable function, and the simulated data were similar from the experimental ones.     

Time domain nuclear magnetic resonance to monitor mass transfer mechanisms in apple tissue promoted by osmotic dehydration combined with pulsed electric fields

Pulsed electric field (PEF) technology is gaining momentum as a pre-treatment to enhance mass transfer of vegetable tissues obtained by further processing. In this study PEF pre-treatment increased osmotic dehydration (OD) effectiveness, in terms of water loss and solid gain in apples, as a function of electric field strength and number of pulses. Mass transfer was particularly high when average electric fields of 250 and 400 V cm^-1 were applied. Time domain nuclear magnetic resonance (TD-NMR), with the use of a contrast agent, clarified structural changes that drive mass transfer. Treatments at 100 V cm^-1 redistributed water between vacuole, cytoplasm and extracellular space, while at 250 and 400 V cm^-1 the membrane breakages caused the loss of cellular compartmentalization. Two non-destructive and fast acquirable parameters, the longest measured relaxation time (T₂) and water self diffusion coefficient (D_w), allowed the separate and accurate observation of PEF treatment and osmotic dehydration effects.Industrial relevanceThe developed non-destructive method, here described, allows the measure of the effects of PEF treatment on apple tissue which can be exploited to have reliable control of the process within minutes. Since mass transfer parameters depend on subcellular water redistribution, the present work provides a tool to boost the development and optimization of agri-food processes on fresh vegetable tissues.     

Effect of osmotic dehydration on dielectric properties,microwave vacuum drying kinetics and quality of mangosteen

Mangosteen (Garcinia mangostana Linn.) with and without osmotic dehydration (OD) in sucrose solution was dried by microwave vacuum drying at 1200, 1440 and 1680 W. Because of water loss (49.12–49.98 g 100 g^?1) and solid gain (9.31–11.62 g 100 g^?1) during OD, dielectric constant, loss factor and loss tangent of mangosteen were significantly increased (P ≤ 0.05) to 24.82–25.12, 11.52–14.18 and 0.47–0.50, respectively. With the decreased initial moisture content and the modified dielectric properties, drying time of osmotically dehydrated mangosteen was shorter than that of mangosteen without OD. Moreover, an increase in microwave power enhanced drying kinetics. With OD, Tg of dried mangosteen was increased from ?7.01, ?3.00 to 11.11–25.96 °C. Hardness and lightness (seedless part) were significantly increased (P ≤ 0.05). Structure of dried seedless mangosteen was well protected, resulting in the improved rehydration ability (P ≤ 0.05). Nonetheless, rehydration ability of the mangosteen containing seed was not improved (P > 0.05).     

Multi-Objective Optimization of Osmotic–Ultrasonic Pretreatments and Hot-Air Drying of Quince Using Response Surface Methodology

In this study, application of a multi-objective optimization technique based on response surface methodology has been presented. Quince slices were dehydrated using osmotic dehydration with sucrose solutions at different concentration (40 and 60 Brix), processing time (1, 1.5, and 2 h), and ultrasonication time (0, 15, and 30 min) were the factors investigated with respect to water loss, solid gain, and weight reduction. Response surface methodology was used to determine the optimum processing conditions that yield maximum water loss and weight reduction and minimum solid gain during osmotic dehydration of quinces. Dehydrated quince slices at optimized osmo-ultrasound condition were then subjected to air-drying at 60 and 80 °C. Rehydration ratio, shrinkage, and moisture content of dried samples were regarded as responses to the non-thermal and air-drying conditions. Multi-objective optimization led to obtaining the best condition for production of dried quince slices with lowest moisture content, and shrinkage.