An Equation for Modelling the Kinematic Viscosities of Binary and Ternary Solutions with Sugars and Sodium Chloride as a Function of Concentration and Temperature Experimental Data of Solutions with Lactose

An equation to model experimental data of kinematic viscosities of aqueous solutions commonly employed in osmotic dehydration is proposed in this article. The binary and ternary systems are constituted by water as solvent and by sugars (sucrose, glucose, and lactose) and glycerol with or without sodium chloride as solutes. Experimental data of kinematic viscosity of aqueous lactose solutions (with and without sodium chloride) are determined in this work. The range of concentration of all systems studied covers the typical experimental conditions of interest (from 0 to 5.0 mol kg^?1 for sodium chloride and 0 up to 0.5 mol kg^?1 for lactose) in this type of processes and temperature varied from 20 to 50°C. The parameters of the equation proposed for each system were optimized and the resulting expression adjusted experimental data with deviations less than 3.0%.     

Effect of stirring in the osmotic dehydration of chestnut using glycerol solutions

The use of osmotic dehydration like a previous step to drying process could be an interesting option in order to reduce costs or to preserve the characteristics of food material. This work studies the osmotic dehydration operation of chestnuts (Castanea sativa M.) with aqueous solutions of glycerol (25, 35, 45 and 60 g/100 g) and glycerol and salt (35 and 9.7 g/100 g, respectively), at different soaking times (1, 2, 4 and 8 h) at 20 °C. In order to evaluate the hydrodynamic effect of osmotic medium on the mass transfer rate, static and dynamic conditions have been tested (0, 40 and 110 rpm). The process was monitored employing several parameters related to moisture content and solid gain changes.Water loss rate using binary solutions increases with glycerol concentration and no dependency was detected with stirring level using glycerol concentration higher than 35 g/100 g. WL/SG ratio increases with glycerol concentration and linear behaviour between WL/SG and water activity of solution was established. NMC contents decrease with glycerol concentration up to 0.78 at 8 h of osmotic dehydration and NSC contents increase with glycerol concentration up to 1.12.WL kinetics using ternary solutions composed by glycerol and sodium chloride solutions were similar to the obtained with glycerol solutions at the same water activity range, but SG kinetics is improved by the acquisition of sodium chloride by the chestnut. In this way, the WL/SG ratio and NMC are lower.Model proposed by Peleg was satisfactorily employed to fit the experimental NMC and NSC data for both binary and ternary solutions considering that equilibrium value is no dependent on stirring level.     

Osmotic dehydration of the Indian fig (Opuntia ficus indica) with binary and ternary solutions

The objective of this work was to study osmotic dehydration (OD) of the Indian fig with two binary solutions (sucrose/water and glucose/water) and a ternary solution (sucrose/NaCl/water) according to a 2³ factorial design with independent variables: temperature (30–50 °C), immersion time (90–240 min) and concentration (40–60 °Brix). The dependent variables were water loss (WL), solid gain (SG) and dehydration efficiency index. The temperature had greater influence on the WL in the three hypertonic solutions studied; the concentration had greater influence on the SG in the three hypertonic solutions investigated and the best conditions for the OD of the Indian fig were in glucose solution at 40 °Brix, 40 °C and 165 min.     

Rheological modelling of binary and ternary systems of tragacanth, guar gum and methylcellulose in dilute range of concentration at different temperatures

Aqueous binary systems of tragacanth, guar and methylcellulose in dilute range of concentration up to 0.1% w/v were studied by means of capillary viscometry at 25.0, 35.0, 45.0 and 55.0 °C and were characterised through their intrinsic viscosities and the corresponding Huggins and Kraemer constants. The viscosity-average molecular weights were calculated and were according to previous reported data.Ternary dilute mixtures were studied as a function of polymer concentration and ratio. A model based on the kinematic viscosity was proposed for the ternary systems by means of the excess viscosity and corresponding parameters of interaction were determined. The model fitted satisfactorily the experimental data at the studied temperatures. Viscosity of the ternary systems increased with the intrinsic viscosity of the main polymer in mixture. The effect of the temperature (25-55 °C) in each obtained model is also discussed.     

Effect of Maltodextrin,Sodium Chloride,and Liquid Smoke on the Mass Transfer Kinetics and Storage Stability of Osmotically Dehydrated Beef Meat

Osmotic dehydration is a non-thermal process for water removal from foods. The aim of the present study was (i) to investigate the effect of binary (NaCl and water) and ternary (maltodextrin, NaCl, and water) osmotic solutions with or without 0.5% liquid smoke on moisture loss, solids gain, and salt content during osmotic dehydration of beef meat and (ii) to evaluate the microbiological and oxidative stability of the processed meat. Osmotic processing resulted in 8.01–13.15% water loss and 3.53–7.59% solids gain depending on the concentration of the osmotic medium. Liquid smoke did not affect mass transfer phenomena (P > 0.05), except for the treatment with 25% NaCl. The applied models for the estimation of the apparent coefficients demonstrated a good fit with experimental data. The simplified Fick’s equations produced the best results. Osmotic treatment with binary and ternary osmotic solutions reduced total aerobic viable microbial counts (P > 0.05) of meat during storage at 4 °C for 9 days. Liquid smoke did not affect microbial counts, but it was very effective in inhibiting lipid oxidation during storage. The results demonstrate that osmotic dehydration with the addition of liquid smoke could effectively increase the shelf life of beef meat by at least 2 days.     

The prediction of water activity of some supersaturated non-electrolyte aqueous binary solutions from ternary data

Binary data are required for prediction of the water activities of multicomponent aqueous solutions by various methods. At high concentrations, these methods would need binary data beyond the solubility limits of individual solutes. Such supersaturated data are usually lacking or very difficult to determine experimentally. The Zdanovskii–Stokes–Robinson equation, which has been shown to be a reliable and accurate method for predicting the water activity of complex solutions, may be applied in reverse to calculate the water activities of supersaturated binary solutions from ternary data. Hitherto unpublished supersaturated binary a _w data of mannitol, sucrose and urea obtained using this method as well as polynomials for their prediction are presented in this paper.     

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.     

Interaction between copper chloride and caffeine as seen by diffusion at 25 °C and 37 °C

A Taylor dispersion method is used to measure ternary mutual diffusion coefficients (D₁₁, D₂₂, D₁₂ and D₂₁) for aqueous solutions of CuCl₂ (1) + caffeine (2) + H₂O-(3) at 25 °C and 37 °C at carrier concentrations from (0.000 to 0.020 mol dm⁻³), for each solute, respectively. The results are compared with these obtained for the binary systems, that is, CuCl₂ (1) + H₂O (2) and caffeine (1) + H₂O (2), also reported here. From these data it is possible to make conclusions about the influence of the caffeine solutes in diffusion of copper chloride.     

Volatile profile of dehydrated cherry tomato: Influences of osmotic pre-treatment and microwave power

Vegetable flavour is a quality characteristic for consumer acceptability. Sun and air are traditionally used for drying tomatoes; however, the optimal combination of techniques such as osmotic dehydration or microwave-assisted air-drying could lead to high quality self-stable products. The aim of this paper was to study the influence of different process variables on the volatile profile of dehydrated cherry tomato halves. The analysed variables were: air-drying temperature (40 and 55 °C), microwave power (0 and 1 W/g) and previous osmotic dehydration with a 55 Brix binary sucrose solution at 30 °C for 120 min (OD1) or ternary solution of 27.5% sucrose + 10% NaCl (w/w) at 40 °C for 60 min (OD2). Twenty major volatile compounds were identified in fresh tomatoes. Among them, 2-isobutylthiazole and 6-methyl-5-hepten-2-one stand out as impact volatile compounds. Dehydration modified the volatile profile, mainly due to the changes induced in some typical fresh-like tomato compounds, but also due to the generation of five new compounds: 1-butanol, 2-methyl-2-butenal, 3-hydroxy-2-butanone, furfural, acetonitrile, related to Maillard reactions, and the catabolism of carotenoids and polyunsaturated fatty acids. Principal component analysis showed the possibility of obtaining dried cherry tomatoes with different volatile profiles, depending on drying conditions.     

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.     

Shrinkage, density, porosity and shape changes during dehydration of pumpkin (Cucurbita pepo L.) fruits

The aim of this work was to study the changes in volume, density, porosity and shape factors of pumpkin tissue during osmotic dehydration (OD) and air drying (AD). Pumpkin cylinders with length/diameter ratio of 5/3 were used. OD experiments were carried out with solutions of sucrose, sodium chloride and mixtures of both solutes at different temperatures. AD experiments were conducted at 70 °C. Volume of samples decreased linearly with weight reduction (WR). Bulk density varied in a restricted range (5-13%) during dehydration and for all the methods maximum values were found. Particle density increased during both processes. Porosity increased at advanced degrees of dehydration, showing a minimum value at the beginning of OD and AD. The proposed models to evaluate shrinkage, bulk and particle densities and porosity from WR were satisfactorily applied. Image analysis showed that shrinkage of samples during OD was isotropic. Pumpkin cylinders increased elongation and decreased roundness and compactness during osmotic dehydration.     

Numerical modelling of conjugate heat and mass transfer during hydrofluidisation food freezing in different water solutions

A novel method of hydrofluidisation food freezing is numerically investigated in this paper. This technique is based on freezing small food products in a liquid medium under highly turbulent flow conditions when the heat transfer coefficient is higher than 1 000 W⋅m⁻²⋅K⁻¹, which depends on the operating and flow conditions. A numerical model was developed to characterise the freezing process in terms of the heat transfer and diffusion of liquid solution components into the food product. The study investigates the freezing process of spherical samples in binary solutions of ethanol (30%) and glycerol (40%) and ternary solution of ethanol and glucose (15%/25%). The developed model was employed to determine the concentration of the liquid solution in food samples and to quantify the effect of sample size, heat transfer coefficient, solution temperature and concentration on the process. The food sample size varied from 5 to 30 mm, and the heat transfer coefficients varied from 1 000 to 4 000 W⋅ m⁻²⋅ K⁻¹. The results confirm that a freezing time of 15 min for 30 mm diameter samples or less than 1 min for 5 mm diameter samples can be achieved with the hydrofluidisation method. The solution uptake was influenced by the solution type, sample size and process parameters and varied from 8.9 to 35 g of solute per kg of product for ethanol-glucose and glycerol solutions, respectively. This paper quantifies the advantages and possible limitations of hydrofluidisation, which has not yet been entirely studied, especially in terms of the mass absorption of different solutes.     

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 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.     

Electronic nose to study postharvest dehydration of wine grapes

Montepulciano grapes were dehydrated at 10 and 20 °C, 45% RH and 1–1.5 m/s of air flow. Samplings were performed at 10%, 20%, 30%, and 40% of weight loss (wl). TSS (total solids content) increased up to 43° and 36° Brix at 20 and 10 °C, respectively, in 27 and 48 days. A straight regression line between M (kg water/kg dry matter) loss and days of dehydration with R² values, equal to 0.97, was found but an angular coefficient of −0.048 and −0.038, respectively at 20 and 10 °C indicated a different rate of weight loss. Volatiles compounds profile changed significantly with the temperature during the dehydration process. Anaerobic metabolites such as ethanol, acetaldehyde, and ethylacetate were much higher at 20 °C than at 10 °C and rose progressively, while at 10 °C, the significant rise was observed between 30% and 40% weight loss. Alcohols and esters prevailed at 20 °C while at 10 °C larger abundances of aldehydes and terpene alcohols are observed. PCA analysis of GC/MS confirmed the volatiles compounds separation between the samples held at 20 and 10 °C. A progressive evolution of the profile is observed for the samples held at 20 °C while those held at 10 °C show a change of volatiles compounds profile only at 40% wl. Loadings analysis show that aldehydes and terpenols are oriented towards the direction of 10 °C samples while alcohols and esters in that of 20 °C samples. The behaviours of GC/MS data were partially corroborated by the data of electronic nose. Electronic nose was able to follow the progressive change of aroma profile at 20 °C while at 10 °C grouped the responses obtained at 10%, 20%, 30% wl all together but at 40% wl, it discriminated the aroma response. This result opens a window on the potential use to monitor commercially the grape dehydration.     

Kinematic Viscosity of Aqueous Solutions of Ethanol and Glucose in the Range of Temperatures from 20 to 45°C

The purpose of this investigation was to determine, using a capillary viscosimeter, kinematic viscosity data of aqueous solutions of ethanol and glucose, at several temperatures (from 20 up to 45ºC) and concentrations. Glucose solubility strongly depended on ethanol concentration allowing the kinematic viscosity study (from 5% up to 45% w/w ethanol concentration with variable glucose concentrations as a function of its solubility). Kinematic viscosity modelling with solution concentration and temperature simultaneously, based on previous models for respective binary systems, was successfully carried out. The estimated values by this model give low average deviations (2.62%) from the experimental data. Glucose solubility (at 25ºC) in alcohol solutions and index of refraction (at 20ºC) of ternary solutions were also determined and empirical models are proposed in order to evaluate both physical properties with high (R² > 0.993 and >?0.991, respectively) accuracy.     

How to deal with visco-elastic properties of cellular tissues during osmotic dehydration

In this work, vacuum impregnated apple discs with different isotonic solutions (sucrose and trehalose) were equilibrated during osmotic dehydration (55°Brix glucose at 40 °C). Changes in sample composition (water and soluble solid contents), weight and volume are analysed. A mathematical model is proposed to describe and quantify the outflow of water from the protoplast as well as the visco-elastic behaviour of the cell. Good correspondence between simulated and measured data of non impregnated samples and samples impregnated with isotonic solutions of sucrose or trehalose during long term osmotic dehydration is obtained. Fitted values of the cell permeability correspond well with tabulated values. Furthermore, also the obtained values of the parameters describing the mechanical properties of the cell wall and Hectian strands seem to reflect the observed structural development of these structures for the different treated samples well.