Effect of the solute on the development of compositional profiles in osmotic dehydrated apple slices

Apple (cv. Granny Smith) slices, 30-mm thick, were osmotically dehydrated for 9 h at 30 °C using glucose, sucrose and trehalose solutions with the same water activity (a_w = 0.96). After OD treatment, water and solute content were analysed in 1.5-mm thick serial disks of the apple slices to determine the effect of osmotic dehydration on the compositional profiles. Diffusional and “Advancing Disturbance Front” (ADF) models were applied to the experimental data, both showing a good fit. Changes in the compositional profiles of osmotically dehydrated slices were also analysed throughout storage time. For this purpose, the 30-mm thick dehydrated slices were kept at 10 °C for 7 days in hermetic plastic bags and compositional profiles were analysed after 1, 2, 3 and 7 days and modelled using Fermi's equation. Throughout storage, the profiles became flatter due to the counter-current migration of water and solutes associated to the concentration gradients. Mass transfer rate during dehydration was faster when sucrose or glucose was used, but trehalose implied an increase in the mass transfer resistance of the tissue. This behaviour was also observed in the mass transfer processes during storage. This effect was attributed to the changes induced by trehalose in the permeability of cell membranes through component interactions.     

Preserving Melons by Osmotic Dehydration in a Ternary System Followed by Air-Drying

In this study, the effect of different osmotic solution concentrations (20–60% w/w of sucrose with 10% w/w NaCl salt), fruit to solution ratios (1:9–1:3), immersion times (0.5–4 h), and temperatures (15–55°C) on the mass transfer kinetics during osmotic dehydration of melons (Curcumis melo L.) in ternary solution namely sucrose–salt–water followed by air-drying were investigated. The effective diffusion coefficients for sucrose and water during osmotic dehydration were determined, assuming osmotic dehydration to be governed by Fickian diffusion. The estimated parameters allowed optimizing the system to reduce total processing time. The optimum treatments were with 50% sucrose and 10% NaCl salt concentration, fruit to solution ratio of 1:4 for 1 h at 45°C. Samples non-treated and pre-treated in optimized conditions were dried in a hot-air dryer at 60°C until equilibrium was achieved after 2.5 h. Pre-treatment reduced the air-drying period in up to 6.8 h.     

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.     

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.     

Adsorption isotherm and heat of sorption of fresh- and osmo-oven dried plantain slices

Firm ripe plantain was transversely cut into 10-mm slices and osmotically pretreated in 52 °, 60 ° and 68 °B sucrose solutions, for 12 h at 25 °C. Fresh- and osmosed plantain slices were air-dried in a cross flow forced draught oven at 60 °C for 72 h. Adsorption isotherms of the products were determined at 20 °C and 40 °C, using a gravimetric-static method. Adsorption data were fitted into eight isotherm models. Isosteric heat of sorption was calculated using the Clausius-Clapeyron equation. Adsorption isotherms of fresh- and osmo-oven dried plantain slices followed type I (J-shaped) isotherms, characteristic of high sugar products. Inversion of 20 C and 40 C isotherms occurred between a_w 0.65 and 0.70. Among the models tested, the Guggenhein Anderson deBoer (GAB) gave the best fit. Isosteric heat of sorption increased with decreasing moisture contents. Negative isosteric heat of sorption occurred at high moisture content. Moreover, isosteric heat of sorption increased with increase in sucrose solution concentration during the osmotic dehydration prior to oven drying.     

Electronic Nose to Detect Strawberry Aroma Changes During Osmotic Dehydration

ABSTRACT:  An electronic nose was used to detect the aroma evolution of strawberry fruits, cultivar "Camarosa," during the osmotic dehydration in sorbitol and sucrose solutions. Strawberry slices were subjected to osmotic dehydration at 30 °C for 1, 2, 4, and 6 h using either 60% sucrose or 60% sorbitol solutions. Volatile compounds of fresh and processed strawberry slices were analyzed by electronic nose and gas chromatography. Electronic nose was able to reveal changes in the aroma profile during processing and permitted differentiation between dehydrated strawberry samples obtained by different osmotic treatments. The electronic nose has the advantage of being simple, rapid, and nondestructive. Such characteristics and the promising results of this work suggested that this device could be a useful and innovative tool to monitor strawberry aroma changes during osmotic dehydration, providing real-time information about the effects of processing conditions and allowing the optimization of technological parameters.     

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.     

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.     

Process conditions effect on the quality of banana osmotically dehydrated

Banana is greatly perishable and does not resist freezing, hence dehydration is the preservation technique of choice. This paper deals with the effect of process conditions on both the dehydration kinetics and the final quality of banana osmotically dehydrated. Banana slices (5 mm thick, 23 mm diameter) were osmotically dehydrated for 4 h, following a 3² full factorial design (temperature (30, 40, and 50 °C), sucrose concentration (45, 55 and 65% w/w)) with experiments in triplicate. The kinetics of dehydration efficiency (DE) and mass loss (DM) and the quality of osmotic dehydrated banana, was analysed through the measurement of colour, final volume (V/V⁰) and shape changes (SF).Both temperature and sucrose concentration in the osmotic solution had a significant effect on DE but had no significant effect on DM. Peleg’s equation fitted well the data for DM and DE during OD. Sucrose concentration and temperature, had no significant effect on DM after 4 h OD or at the equilibrium mass loss (DM^e) (p > 0.05), however, temperature had a significant effect on the initial rate of DM (p < 0.05). Sucrose concentration and temperature, had no significant effect on the colour parameters (L, Chroma and Hue), but showed a significant effect on V/V⁰ and SF, with temperature having a more extensive negative impact on V/V⁰ and SF than sucrose concentration. Process temperature (low temperature, e.g., 30 °C) has to be carefully selected in order to reach a compromise between OD rate and an appropriate final product quality. The reduction in the kinetics caused by low temperature could be compensated by using highly concentrated sucrose solutions (as much as 65%), which would favour the compositional changes with a lesser impact on the product quality.     

Effects of electrical pretreatment conditions on osmotic dehydration of apple slices: Experimental investigation and simulation

Electrical pretreatments at 9 different conditions consisting of the combination of 3 different voltage gradients (20, 27, and 32 V/cm) and 3 different application times (10, 20, and 30 s) were applied on apple slices. Apple slices were osmotically dehydrated in 50% sucrose solution at 40 °C until their total dry matter content (TDM) reached to 40%. The effect of pretreatment conditions on the change of water loss and solid gain during osmotic dehydration was investigated, and effective diffusion coefficients were determined. The time needed to reach up to 40% TDM content was predicted by using the numeric solution of unsteady state mass transfer equations and diffusion coefficients via MATLAB code written. The electrical pretreatments reduced the osmotic dehydration time by in the range of 26–64%. The final water and solid distributions of apple slices were simulated in ANSYS. Modeling and simulation results were in good agreement with experimental data (p < 0.05).Industrial relevanceSince the electrical pretreatment both shortens the osmotic dehydration time and increases the water removed per unit energy used, its application prior to osmotic dehydration processes in the commercial productions will be economical. The proposed modeling and simulation approach for assessment of the effects of electrical pretreatments on osmotic dehydration characteristics may provide valuable information on the scaling up of these conditions in the industrial scale systems.     

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.     

Influence of sugar composition on water sorption isotherms and on glass transition in apricots

Desorption isotherms of fresh and osmotically treated (70%, 30 °C) apricots have been measured at 30, 45 and 60 °C by the static gravimetric method. A differential scanning calorimeter was used to determine the T_g of samples equilibrated with several water activities. The osmotic pretreatment affected the shape of the desorption isotherms because of biopolymer binding at low activities values and dissolution of sucrose at high activities values. At 45 °C, isotherms of fresh and sucrose impregnated apricots are identical. At 60 °C, sucrose impregnation depressed water activity, while at 30 °C the opposite effect is observed. Evolution of moisture content at the first saturation layer expresses these effects of sucrose impregnation and temperature. Peleg model fitted the best experimental desorption isotherms of the fresh and osmotically treated apricots (0.990 ? r² ? 0.999, 0.005 ? S ? 0.045). A strong plasticizing effect of water on the T_g was found, with a great reduction in this value with increase in water activity.     

Effect of osmotic dehydration on the quality of air-dried Porphyra

Osmosis with a solution of NaCl and sucrose to depress the water activity (a_w) to 0.970 and the pH to 3.0 was assayed as a pretreatment to air-drying of red seaweeds (Porphyra columbina Montagne). Air-drying was performed at 30°C and 14% relative humidity. Process characteristics, color, flow pattern and rehydration ability of the milled product, were evaluated to determine the usefulness of osmosis. The a_w attained after 2 h of drying was similar for both osmosed and nonosmosed Porphyra and higher than monolayer water activity for both products. Consequently, no additional benefits concerning stability during storage were observed, after applying osmosis. Moreover, severe changes in color occurred. Powder flowability evaluated through the measurement of compressibility and cohesiveness decreased with pretreatment, which also determined a more plastic behavior. In summary, osmotic dehydration as a pretreatment for air-dried seaweeds did not seem to improve the final product quality.     

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.     

Application of High Hydrostatic Pressure as a Pretreatment for Osmotic Dehydration of Banana Slices (Musa cavendishii) Finish-Dried by Dehumidified Air Drying

The process variables high hydrostatic pressure (HHP; 100–500 MPa), sucrose concentration (30–70 °Brix), immersion time (5–9 h) and immersion temperature (30–70 °C) were optimised to yield maximum water loss (WL), minimum solid gain (SG), minimum water activity (a _w) and minimum browning index (BI) during osmotic dehydration (OD) of banana slices (Musa cavendishii) pretreated by HHP using response surface methodology. The pressure-treated samples showed significantly higher WL and SG during OD (p?<?0.05), which was attributed to the rupture of cell wall with applied pressure, making the cells more permeable, also evident from the scanning electron micrographs of the banana tissue. The optimised operating conditions were: HHP of 200 MPa for a dwell time of 5 min at room temperature (26 °C), sucrose concentration of 60 °Brix, immersion time of 5 h and immersion temperature of 40 °C. A study of the concentration profiles during OD revealed no appreciable increase in SG and WL after 4 h; hence, immersion time was reduced to 4 h. The optimised product developed was dried to a moisture content of 15 % (wet basis) in a dehumidified air dryer at an air temperature of 40, 55 and 70 °C with a fixed air velocity of 3.8 m/s and relative humidity maintained at 20 %. The final dried product was analyzed for total soluble solids content, BI and a _w. A drying temperature of 55 °C was found to give superior quality OD banana slices in terms of reduced bulk, improved flavour, decreased a _w (<0.60), and reduced dehydration time and energy using HHP as a pretreatment.     

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.     

Dehydrofreezing of pineapple

Dehydrofreezing technique involves one step of partial dehydration before freezing, in order to diminish the tissue damage by removing part of water from vegetable tissue prior to freezing. The objective of the present study was to evaluate the effect of osmotic dehydration and hot air-drying, applied previous to the freezing process, on the end quality of pineapple slices. Quality loss was quantified through drip loss, ascorbic acid content and mechanical properties changes of tissue. Freezing was carried out in a conventional air-blast tunnel at −31.5 ± 2 °C. Mechanical properties of fresh and dehydrated fruit, with and without the later process of freezing, were evaluated through compression tests. Ascorbic acid content was quantified by liquid chromatography. Osmotic dehydration and hot air-drying have the beneficial effect of reducing the time necessary for pineapple samples freezing. The freezing–thawing process affects the values of pineapple samples mechanical properties. Ascorbic acid losses were somewhat greater during the osmotic dehydration than with air dehydration.     

The potential role of isothermal calorimetry in studies of the stability of fresh-cut fruits

Attention is drawn to the feasibility of using high sensitivity isothermal heat conduction calorimetry to study metabolic responses of differently processed and stored fresh-cut fruit. The heat production of endogenous (tissue metabolism during 12 h of analysis at 10 °C for kiwifruit and strawberry) and exogenous (microbial growth during 18 d of analysis at 10 °C for cantaloupe) biological processes was investigated.Osmotic dehydration of fresh kiwifruit in sucrose solution (61.5 g/L) at different treatment times (30, 60 and 180 min), resulted in metabolic heat production decrease, confirming the progressive cell death induced by osmotic dehydration.Analysis on strawberry slices under two atmospheric conditions (air and innovative modified atmosphere) seemed to confirm the inhibitory effect of N₂O on metabolic activity.Cantaloupe samples immersed in three different syrups (SS: sucrose syrup (20 °Brix); SS₁: SS + 0.5 g/L ascorbic acid + 0.5 g/L citric acid; SS₂: SS₁ + 0.1 g/L potassium sorbate) showed a stability increase when additives with antimicrobial properties were included.Our findings confirm that isothermal calorimetry provides a versatile and high sensitive tool for conducting fundamental metabolic studies on the effect of different processing operations on the quality and shelf life of fresh-cut fruit and vegetables.     

Osmotic dehydration of Aloe vera (Aloe barbadensis Miller)

Aloe vera possess immunomodulatory, anti-inflammatory, antibacteria effects and wound and burn healing properties, but it is a very unstable product due to its high water content. Osmotic dehydration can be used to obtain stable products from aloe. In this work the effect of osmotic dehydration (OD) on Aloe vera (Aloe barbadensis Miller) leaves was studied. Peeled and unpeeled Aloe vera slices (15 × 50 mm), were immersed in sucrose solutions at 35, 50 and 65 °Brix at 25 and 40 °C. Moisture, effective diffusion coefficients and mass fluxes (water loss, solids gained and weight reduction) were determined. Osmotic dehydration experiments were conducted at atmospheric pressure. The best conditions for the OD of Aloe slices with the highest effect on diffusivity were obtained using a temperature of 40 °C for peeled samples. The analysis of the effect of temperature on mass transfer kinetics showed that unpeeled samples were more effected than peeled samples.     

EFFECT OF CaCl2 AND CONVECTIVE-OSMOTIC DRYING ON TEXTURE AND PREFERENCE OF APPLE

Conventional air‐drying combined with osmotic dehydration was researched as a potential method for drying apple cubes of superior quality. Samples were pretreated with CaCl₂ at different temperatures and times. Pretreated apple cubes were dehydrated in a tray dryer. Then, osmotic dehydration with sucrose solutions was carried out. The curves for osmotic dehydration showed that the gain of solids was higher when 40% of water was removed by convective drying while the loss of weight was lower at the same level of dehydration at 65°Brix. Texture measurements indicated that the temperature of pretreatment affected the hardness and cohesiveness. Hardness values were higher at 40C, while cohesiveness values were lower at the same temperature. The CaCl₂ at a given temperature did not have a significant effect on texture. Sensory evaluation showed that samples pretreated at 25C and osmotically dried at 50°Brix had the higher preference by the judges.