Evaluation of Factors Influencing Microwave Osmotic Dehydration of Apples Under Continuous Flow Medium Spray (MWODS) Conditions

Microwave osmotic dehydration under continuous flow medium spray (MWODS) conditions is an innovative concept with high potential for enhancing moisture loss as well as improving product quality. Quantification of mass transfer kinetics under different processing conditions is important for managing and optimizing the osmotic dehydration process. A response surface methodology was used for evaluating and quantifying the moisture loss and solids gain kinetics of apples during the MWODS process. Experiments were designed according to a central composite rotatable design with all independent variables included at five levels (sucrose concentration, 33.3–66.8°Brix; medium temperature, 33.3–66.8 °C; medium flow rate, 2,120–3,480 ml/min; and medium contact time, 5–55 min). The process responses were moisture loss (ML), solids gain (SG), and weight reduction (WR) and were related to process variables using second-order polynomial regression models. The lack of fit was not significant (p?>?0.05) for any of the developed models. For ML, SG, and WR, the medium contact time was the most significant factor during the MWODS process followed by medium temperature and sucrose concentration. The effect of medium flow rate was only significant with moisture loss and weight reduction. The quantity of ML, SG, or WR achieved over a 30 min treatment time was chosen as the drying rate. These rates were shown to be responsive to the osmotic treatments increasing with sucrose concentration, medium flow rate, and medium temperature.     

Optimisation of osmotic dehydration process of carrot cubes in mixtures of sucrose and sodium chloride solutions

In the optimisation of the osmotic dehydration process of the carrot cubes in mixtures of sucrose and sodium chloride by response surface methodology, using face-centred central composite design (CCF), it was shown that the independent process variables for osmotic dehydration process were osmotic solution concentrations (5–15% w/v sodium chloride in 50 °Brix sucrose syrup), temperature (35–55 °C) and process duration (120–240 min). Statistical analysis of results showed that the linear terms of all the process variables have a significant effect on all the responses. The optimum osmotic dehydration process conditions for maximum water loss, minimum solute gain, maximum retention of colour, and sensory score were: 50 °Brix + 15% w/v sodium chloride solution, 54.8 °C solution temperature and 120 min process duration.     

Osmotic concentration of potato.

A study was conducted to determine what conditions define the equilibrium state between potato and osmosis solution for an osmosis concentration process. It was shown that at equilibrium, there is an equality of water activity and soluble solids concentration in the potato and in the osmosis solution. Rinsing the surface of the potato after osmotic concentration was shown to significantly reduce solids gain and soluble solids concentration in the potato, thus resulting in a sizeable increase in the potato water activity.
When water loss, solids gain, change of water activity and economics are considered, the optimal conditions for an equilibrium osmosis with sucrose would use a 50% solution at a solution/solids ratio of 4. Uptake of solids during sucrose-based osmosis results in 75% of the soluble solids in the equilibrated potato coming from the osmosis solution. A comparison of various osmosis solutions at a 60% total solids level shows that mixed sucrose-salt solutions give a greater decrease of water activity than the pure sucrose solution, even though the mass transport data are similar, this undoubtedly being due to the uptake of salt.
A model has been developed for calculation of osmosis mass transport data and water activity for osmotic concentration to equilibrium in sucrose solutions for the concentration range 10–70% and solutionlsolids range of 1–10. The mass transport data can be calculated with an average error < 4%. Water activity can also be predicted with good accuracy for the range of parameters normal for osmosis concentration processes. The proposed model was also able to predict osmosis mass transport data and water activity data for short, non-equilibrium osmosis times.     

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.     

Kinetics of osmotic dehydration of red bell peppers as influenced by pulsed electric field pretreatment

This study was aimed at relating diffusion rates during osmotic dehydration of red bell peppers in two different osmotic solutions (sucrose/sodium chloride, 21.86 and 2.02 g/100 g respectively, and sucrose, 50°Brix at 30 °C) to the extent of membrane permeabilisation induced by pulsed electric field (PEF) using varying field strength of 1, 1.5 and 2 kV/cm with a constant pulse number of 20 at a pulse duration of 400±50 μs. The development of pores with time within the membrane after PEF was monitored, changes in sample weight and composition in the product liquid phase were analysed. The initiation of pore formation and pore growth within the cell membrane after PEF was found to be time dependent and not an instantaneous process. A fractional ruptured membrane area, F_p=0.003% was detected after about 20 s of application of 2 pulses at 2 kV/cm (320 J/kg energy input per pulse and approx. 0.2 °C temperature change) and this increased to 0.0166% within 300 min. Osmotic dehydration of bell peppers was highest at the beginning of the process. The application of PEF resulted in enhanced rate of transfers as indicated by an increase of 11–25% in water loss and 2–5% in solids gain as compared to the untreated samples in the two osmotic solutions. Conditions of PEF that induced an average fractional ruptured area of 0.008%, 5 min after PEF treatment were found adequate to markedly improve diffusion kinetics during the osmotic dehydration under atmospheric pressure conditions.     

Effect of Ultrasound-Assisted Osmotic Dehydration as a Pretreatment on Deep Fat Frying of Potatoes

The objective of this study was to investigate the possibility of using ultrasound-assisted osmotic dehydration (UAOD) as a pretreatment prior to frying and to study its effects on the quality of fried potatoes. The quality parameters, moisture content, oil uptake, color, texture, and microstructure of fried potatoes, were chosen. Quality of fried potatoes treated with UAOD was also compared with the ones treated with osmotic dehydration (OD). Potato slabs (40 × 40 × 7 mm) were pretreated with different osmotic solutions (15 % sodium chloride and 15 % sodium chloride/50 % sucrose solutions) at different temperatures (25, 45, and 65 °C) with and without ultrasonic waves for different treatment times. The pretreatment conditions which are OD for 90 min and UAOD for 30 min using 15 % sodium chloride/50 % sucrose solution were applied prior to frying at 170 °C for 2, 4, and 6 min. UAOD reduced the oil content of fried potatoes by 12.5 % (db) as compared to untreated fried potatoes at the end of frying. There was no significant difference between OD and UAOD in reduction of oil uptake in fried potatoes. However, UAOD was found to have the advantage of improving the color of French fries. In addition, it shortened the pretreatment time of OD by about 67 %. Cell structure of fried potato was damaged in the presence of pretreatments of OD and UAOD.     

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.     

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).     

KINETICS OF OSMOTIC DEHYDRATION OF MANGO

The effects of sucrose syrup concentration (40–70 g/100‐g solution) and temperature (40–90C) on water loss and sucrose uptake by mango mesocarp slices during osmotic dehydration were investigated. The effective diffusivities for mass transfer were determined using the slope method based on the Fickian diffusion model. Water loss and sucrose uptake were proportional to the square root of osmotic contact time, implying that the process is Fickian. The specific mass transfer rate constants and effective diffusivities (D_e), derived from Fick's unsteady‐state diffusion equation, increased with temperature and sucrose syrup concentration. D_e values for water loss and sucrose uptake, which ranged between 2.59 × 10^?6 to 5.12 × 10^?6 m²/h and 1.70 × 10^?6 to 4.14 × 10^?6 m²/h, respectively, were related to absolute temperature using an Arrhenius‐type relationship. The activation energies, which fell in the range previously reported for diffusion‐controlled processes, increased with sucrose syrup concentration and varied from 9.74 to15.16 KJ/mol.     

Pulsed Vacuum Osmotic Dehydration of Beetroot,Carrot and Eggplant Slices: Effect of Vacuum Pressure on the Quality Parameters

Pulsed vacuum osmotic dehydration (PVOD) is a widely used technique for reducing moisture content and water activity in biological products. This study aimed to analyze the effect of vacuum application (VA) on PVOD of beetroot, carrot, and eggplant slices, with respect to chemical (moisture, water activity, specific pigments, polyphenols, and sodium content), optical (color), mechanical (shrinkage, maximum stress, and elasticity), and structural (microstructure) properties. PVOD was conducted at three different vacuum pressures (0, 40, and 80 kPa, for 10 min), during a total process time of 300 min. Osmotic processing was performed at 35 °C by using a ternary osmotic solution [40% sucrose +?10% sodium chloride (w/w)]. Eggplant and carrot samples were more sensitive to VA, compared to beetroot. This was related to their porous and less compact structure. In general, VA reduced the moisture content and water activity and preserved the carotenoid content. VA caused loss of betalain and phenolic acid, favored sodium uptake, and induced significant changes in the optical, mechanical, and structural properties, compared to the osmotic processing conducted at atmospheric pressure.     

蓝莓渗透脱水的研究

在不同的渗透温度 ( 4 5～ 65℃ )条件下 ,高果糖浆和蔗糖的有效水分扩散率 (Dm)分别为( 4 90 60～ 5 2 3 66)× 1 0 - 10 m2 /s和 ( 3 5 5 1 8～ 4 0 1 0 9)× 1 0 - 10 m2 /s,有效固形扩散率 (Ds)分别为( 2 7740～ 3 691 5 )× 1 0 - 10 m2 /s和 ( 1 3 1 63～ 2 691 5 )× 1 0 - 10 m2 /s的规律。在渗透脱水处理过程中Dm 和Ds 随处理温度升高而增加。经高果糖浆 ( 70°Brix)渗透脱水的蓝莓的平均体积比随温度升高而稍微下降。其相对密度随温度的升高也略有增加     

ARTIFICIAL CELL STUDIES IN SIMULATED APPLE AND POTATO STARCH CELL COMPLEX DURING OSMOTIC DEHYDRATION

ABSTRACT

Visking tubing was employed as an artificial cell system to investigate the behavior of water in simulated apple and potato starch cell complex during osmotic dehydration. The study involved a factorial experimental design at three levels of temperature (32.2, 40 and 55C) and five levels of solute concentration solutions (four sucrose concentrations: 40, 50, 60 and 70%; one sodium chloride concentration: 0.5%). A time period of 0–3 h was implemented with 30‐min sampling period for every treatment. Three phases of a sharp decrease in the initial weight of the visking tubing in the first 30 min were observed for all temperatures and solute concentrations. In all the treatments, there was an incremental increase in water loss with increased temperature and sucrose and salt concentrations. Water loss was higher for simulated apple and 1% potato starch solutions compared with 15% potato starch solution. Starch in the visking tubing competed for the removal of water during osmotic dehydration. The amount of starch contributed to the differences in the rate of water loss in the visking tubing.

PRACTICAL APPLICATIONS

In order to better understand the behavior of water in simulated apple and potato starch cell complex during osmotic dehydration of plant materials, the Visking tubing was used as an artificial cell in simulating biological membranes. Simulated apple and potato starch was studied as representatives of cellulosic and starchy plant materials, respectively. Notably, there was antagonistic effect between starch and salt solutions, starch and sugar solutions similar to sugar and salt solutions as a result of differences in their molecular weights. This study is industrial applicable to achieve efficient osmotic dehydration processes for plant materials that are cellulosic or starchy in nature.     

Low Temperature Growth of Type E Clostridium botulinum Spores. 2. Effects of Solutes and Incubation Temperature

SUMMARY— The inhibition of outgrowth of spores of Clostridium botulinum Type E by the addition of different concentrations of various solutes to a trypticase-peptone-sucrose-yeast extract medium (TPSY) was studied at different incubation temperatures. Solutes added to TPSY medium were sodium chloride (NaCl), sodium formate (NaCOOH), potassium chloride (KCI), sucrose and glucose. Incubation was at 30, 21.1, 15.6, 10 and 7.2°C, and growth was confirmed by mouse toxin assay. The effect of the solutes on the equilibrium relative humidities (ERHI of the various media was measured using the graphical interpolation method and expressed as water activity (a_w). The possibility of an osmotic effect was also investigated. The molar (M) concentrations and osmotic pressures of the different solutes were calculated and related to the approximate inhibitory concentrations of 5.0% NaCl (a_w 0.975), 6.0% KCI (a_w 0.974), 5.5% NeCOOH (a_w 0.9711, 38.5% sucrose (a_w 0.976) and 22.5%. glucose (a_w 0.970).
The inhibitory salt concentrations were approximately 0.80 M and produced osmotic pressures of about 36.0 atmospheres. The approximate osmotic pressure of the inhibitory 1.12 and 1.24 M sucrose and glucose solutions were 25.08 and 27.97 atmospheres respectively.
Growth response decreased as the incubation temperature decreased as measured by delayed outgrowth times and in decreased amount of cellular material produced by the Type E strains tested.     

MASS TRANSFER IN PLANT MATERIALS IN CONTACT WITH AQUEOUS SOLUTIONS of ETHANOL and SODIUM CHLORIDE: EQUILIBRIUM DATA

A process for osmotic dehydration of plant materials using aqueous solutions of ethanol and sodium chloride is described. Equilibrium data for blanched and unblanched carrots in contact with binary aqueous solutions of ethanol and sodium chloride are presented. Based on the equality of activities of the solutes in carrots and the external solution a successful representation of equilibrium has been obtained in terms of the measurable practical variables such as the total solids in the material at full turgor, solute concentration in the bath and the temperature of contacting.     

Osmotic dehydration of pomegranate seeds: mass transfer kinetics and differential scanning calorimetry characterization

Osmotic dehydration of pomegranate seeds was carried out at different temperatures (30, 40, 50 °C) in a 55°Brix solution of sucrose, glucose, and mixture sucrose & glucose (50:50, w/w). The most significant changes of water loss and solids gain took place during the first 20 min of dewatering. During this period, seeds water loss was estimated to 46% in sucrose, 37% in glucose and 41% in mix glucose/sucrose solution. The increase of temperature favoured the increase of water loss, weight reduction, solids gain and effective diffusivity. Differential scanning calorimetry data provided complementary information on the mobility changes of water and solute in osmodehydrated pomegranate seeds. The ratio between % frozen water and % unfreezable water decreased from 5 to 0.5 during the process. That involving the presence of very tightly bound water to the sample, which is very difficult to eliminate with this process. It also appeared that glass transition temperature depends on the types of sugar.     

A PRELIMINARY STUDY OF W/O/W EMULSIONS WITH A VIEW TO POSSIBLE FOOD APPLICATIONS

A study was made of the influence of various additives on the stability and low shear viscosity of water-in-olive oil-in-water emulsions. The additives were glucose, sucrose, acetic acid, citric acid, ascorbic acid, sodium chloride and sodium acetate, Glucose and sucrose increased viscosity for some time until a constant value was reached. With the other additives an initial increase in viscosity was followed by a decrease and a corresponding decrease in stability. These observations are explained in terms of the osmotic pressure gradient between the inner and outer water compartments, and the effect of additives on the physical state of the emulsifier films adsorbed at the interfaces between the two water compartments and the oil phase.     

APPLICATION OF RESPONSE SURFACE METHODOLOGY FOR THE OSMOTIC DEHYDRATION OF CARROTS

Osmotic dehydrations of carrot cubes in sodium chloride salt solutions at different solution concentrations, temperatures and process durations were analyzed for water loss and solute gain. The osmotically pretreated carrot cubes were further dehydrated in a cabinet dryer at 65C and were then rehydrated in water at ambient temperature for 8–10 h and analyzed for rehydration ratio, color and overall acceptability of the rehydrated product. The process was optimized for maximum water loss, rehydration ratio and overall acceptability of rehydrated product, and for minimum solute gain and shrinkage of rehydrated product by response surface methodology. The optimum conditions of various process parameters were 11% salt concentration, 30C osmotic solution temperature and process duration of 120 min.     

OSMOTIC DEHYDRATION OF APPLES BY IMMERSION IN CONCENTRATED SUCROSE/MALTODEXTRIN SOLUTIONS

The effect of sucrose:maltodextrin (S:M100) ratios on solids gain (SG) and water loss (WL) was investigated during the osmotic dehydration of apple disks. Concentrated solutions were prepared at 40C with 100:0, 90:10, 70:30, 50:50, 30:70 and 10:90 ratios of (S:M100). The highest score in sensory evaluation was achieved with 90:10 ratio of (S:M100). Three stages of osmotic dehydration can be observed by plotting the shrinkage of apple disks vs the moisture content. The result is that a higher maltodextrin concentration favors volume loss and enhances water loss, increasing the duration of stage 2 osmotic dehydration.     

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.     

Dielectric spectroscopy of osmotic solutions and osmotically dehydrated tomato products

Complex permittivity is the physical property that describes the interaction between matter and an electromagnetic field. This property is related to the structural and physico-chemical properties such as water and soluble solids content or water activity of the material.

The complex permittivity of different aqueous solutions, fresh and osmotically dehydrated cherry tomatoes was measured and related to the products’ composition. Results showed that fruits osmotically dehydrated with sucrose solutions reached the lowest loss factors but the maximum penetration depth (D_p). On the other hand, fruits immersed in binary salt solutions showed the inverse tendency. For products impregnated with ternary solutions an intermediate behaviour was observed. Calcium lactate addition had no significant effects on complex permittivity at 2.45 GHz, but its presence increased the effective loss factor at low frequency.

The dielectric properties of fruits and vegetables can be modified by controlling osmotic process variables (time, temperature, pressure and osmotic solution composition) in order to improve their further drying with microwaves.