Simplified method for the prediction of water activity in binary aqueous solutions

This work describes the application of a simplified method to predict the water activity ( a _w) of binary aqueous solutions in a range of concentrations relevant to intermediate moisture foods. The water activity as a function of molality for several solutes (electrolytes and non-electrolytes) is described by the equation, a _w, = 1 − K m , where K is a constant and m is the molality. Values of K are reported for fifteen non-electrolytes and eight electrolytes. The accuracy of water activity prediction by this method satisfies the actual needs in food research.     

Kinematic viscosity and water activity of aqueous solutions of glycerol and sodium chloride

During osmotic dehydration, a removal of water from foodstuffs is achieved with a decrease in the water activity of the food sample. This dehydration process involves the utilization of highly concentrated solutions with one or several solutes that increase considerably the viscosity of the liquid phase. This property is fundamental in the studies of mass and momentum transfer processes. Glycerol and sodium chloride are studied as systems employed in this type of process due to the advantages for the final dehydrated product. Kinematic viscosities of binary and ternary aqueous solutions of these solutes were measured at various concentrations (from 0 to up 5.0 mol kg^–1) and temperatures (from 20 up to 50 °C). Water activities for each indicated solution at 25 °C are also reported. Experimental data for both physical properties were simultaneously correlated with concentration and temperature for binary and ternary solutions with a suitable accuracy. Additionally, relationships between kinematic viscosities and water activities were established.     

Prediction of Lactose Crystals Present in Supersaturated Lactose and Whey Solutions by Measuring the Water Activity

Linear models based on water activity measurement were developed to predict the crystalline fraction of lactose present in the supersaturated crystal-solution mixture of lactose and whey. By this method, it was possible to measure the crystalline fraction in the mixture even if the sample is opaque or coloured, which would be difficult to measure by the conventional refractometric method. To calculate the fraction of lactose crystallized, the differential water activity of the crystallized mixture and non-crystalline supersaturated solution needs to be determined. For the pure lactose, the predictive linear equation was Δ?L = 1874.4 Δ?a_w, whereas for whey it was Δ?L = 1155.2 Δ a_w, where Δ L is the amount of α-lactose monohydrate crystals (g 100g^?1 water) that is in the crystallized solution, and Δ a_w is the differential water activity after and prior to crystallization. Other equations such as Raoult's. Norrish, and Money-Born were also tested to predict the water activity of supersaturated solutions of lactose or whey.     

Determination and correlation of the water activity of unsaturated, supersaturated and saturated trehalose solutions

The water activity (a_w) of unsaturated and supersaturated trehalose solutions (and some sucrose solutions) was determined using a dew point hygrometer, and correlated using an equation originally proposed by Norrish [1966. An equation for the activity coefficients and equilibrium relative humidities of water in confectionery syrups. Journal of Food Technology, 1,25] for predicting water activity in binary non-electrolyte solutions. The a_w lowering behaviour of trehalose was found to be almost identical to that of sucrose solutions at same concentrations; however, due to the lower solubility of trehalose the a_w of their saturated solutions is higher than that of sucrose ones. The a_w of saturated trehalose solutions at 20, 25, 30, 35 and 40 °C was also determined and found to be between 0.953 and 0.928. These values agreed well with predictions made using a_w data for trehalose solutions calculated at the solubility concentration at the various temperatures.     

Mass transfer properties of osmotic solutions. I. Water activity and osmotic pressure

Abstract

In this review paper data on water activity, solute activity and osmotic pressure of”; binary and multi‐component osmotic solutions are provided. The Characteristics of the osmotic solutions are needed for the optimization of mass transfer during osmotic process, and for the improvement of final product quality. The vant Hoff equation and Gibbs Duhem theorem are commonly used to estimate osmotic pressure and solute activity. Water activities can be easily estimated through experimental determination of the freezing point depression. The possibilities of the group contribution models such as the Analytical Solution of Groups (ASOG) approach are also explored. The future needs especially in the case of multicomponent solutions consisting of electrolyte and non‐electrolyte mixtures are pointed out.     

Mass transfer properties of osmotic solutions. II. Diffusivities

Abstract

Mass transport properties of osmotic solutions are important in controlling osmotic dehydration process. In the first paper of the series “Mass Transfer Properties of Osmotic Solutions”;, data of water activities, osmotic pressure, osmosities or osmolalities and solute activities are presented. In the present paper, the literature data on diffusivities of both binary and multi‐component osmotic solutions are presented. Some aspects of measurement methodology and mass transfer modeling are also discussed.     

Estimation of crystalline phase present in the glucose crystal–solution mixture by water activity measurement

The amount of crystalline fraction present in monohydrate glucose crystal–solution mixture up to 110% crystal in relation to solution (crystal:solution=110:100) was determined by water activity measurement. It was found that the water activity had a strong linear correlation (R²=0.994) with the amount of glucose present above saturation. Difference in the water activities of the crystal–solution mixture (a_w1) and the supersaturated solution (a_w2) by re-dissolving the crystalline fraction allowed calculation of the amount of crystalline phase present (ΔG) in the mixture by an equation ΔG=846.97(a_w1−a_w2). Other methods such as Raoult's, Norrish and Money–Born equations were also tested for the prediction of water activity of supersaturated glucose solution.     

Literature Review on Linear Regression Equations for Relating Water Activity to Moisture Content in Floral Honeys: Development of a Weighted Average Equation

A literature review on several existing linear regression equations for correlating water activity (a _w) and refractometric moisture content in floral honeys was performed in order to provide a weighted average regression equation. For this purpose, a meta-analysis of the literature linear equations was made which takes into account the number of data points as well as the precision involved in the different literature studies. The weighted average linear regression equation is a general linear relationship to calculate the honey water activity on the basis of the honey moisture content. It was obtained from comparing and combining the results of ten independent studies involving 638 observations and including honeys from Argentina, Colombia, Spain, Germany, Czech Republic, China, México, Cuba, Brazil, El Salvador, India, and Vietnam. It was also found that the proposed equation describes satisfactorily the water activity of concentrated (and supersaturated) glucose/fructose solutions, which would confirm that these sugars are the main determinants of water activity in honey.     

Increasing calcium solubility from whey mineral residues by combining gluconate and δ-gluconolactone

Insoluble milk mineral residues from whey processing, dominated by hydroxyapatite and calcium hydrogen phosphate, dissolved isothermally in aqueous gluconate/δ-gluconolactone, spontaneously forming solutions supersaturated in both calcium hydrogen phosphate and calcium gluconate. Calcium concentration of maximally supersaturated solutions was proportional to gluconate concentration, indicating gluconate assisted dissolution, while gluconolactone increased calcium available for dissolution and supersaturation. Precipitation of calcium gluconate, rather than of calcium hydrogen phosphate, was critical for supersaturation robustness. For calcium gluconate ionic product:solubility product of calcium gluconate ratios <12, the supersaturated solutions had a lag phase for precipitation of several weeks, which increased to several months by addition of solid calcium saccharate prior to dissolution of the mineral residues. Such supersaturated solutions with up to 7 g calcium L⁻¹, corresponding to a factor of supersaturation of >100 times compared with equilibrium calcium hydrogen phosphate solubility, may be exploited for increasing calcium availability of whey mineral based functional foods.     

Kinematic Viscosity of Ternary Aqueous Solutions of Ethanol and Sucrose

A capillary viscosimeter was used to measure the kinematic viscosity data of aqueous solutions of ethanol and sucrose at several temperatures (from 20 up to 45°C) and concentrations (from 5% up to 95.11% w/w ethanol concentration with variable sucrose concentrations as a function of its solubility). Two models were proposed for fitting the experimental data (one for water/ethanol and another for water/ethanol/sucrose solutions). These models were based in pre-existing equations like Redlich-Kister and Torok-Rard-Miller (for dependency on concentration), and also Vogel-Fulcher-Tamman (for dependency on temperature). The estimated values by these two models gave low deviations from the experimental data for binary and ternary mixtures.     

Water Mobility and Crystallization Action of Lactose-water Systems by Oxygen-17 and Carbon-13 NMR

Systems ranging in concentration from 10-60g lactose/100g water were investigated by fully proton decoupled ¹⁷O and fully proton decoupled ¹³C Nuclear Magnetic Resonance (NMR). The relation between ¹⁷O NMR transverse relaxation rate measurements and lactose concentration showed water mobility decreased linearly with increasing lactose concentration up to 25g lactose/100g water and decreased rapidly and nonlinearly above that level. Water mobility was used to monitor lactose crystallization in supersaturated solutions with time. The 13 C NMR showed no significant differences in chemical shifts of carbon atom peaks in lactose molecules during crystallization. However, depending on the method of sample preparation, mutarotation could be observed.     

A Corrected Ross Equation

A simple method for integrating and extending the binary form of the Gibbs-Duhem equation for routine application in food technology is given. The integrated equation was used to show that considerable solute-solute interaction occurs in mixed solutions which, when corrected for in the Ross equation, results in a revised equation whose predictions of the a_w of mixed solutions more closely agree with measured values. The revised equation indicates that one can obtain accurate estimates of the a_w of a mixed solution by combining estimated water activities with estimated interactions based on the number and concentrations of the solution components.     

近红外光谱在小尾寒羊羊肉水分预测中的应用

以南疆小尾寒羊鲜羊肉的含水量为研究对象,首先采集鲜羊肉的光谱数据和水分含量信息;然后分别采用小波变换、多元散射校正以及二者结合的方法预处理数据;最后使用偏最小二乘法对3种方法预处理过的光谱数据建立羊肉水分含量的预测模型,共制备134个样本,根据留一法选择110个样本作为训练集,剩余的24个样本作为预测集.结果表明,采用...     

Use of analytical solutions of groups (ASOG) contribution method to predict water activity in solutions of sugars, polyols and urea

ASOG (Analytical Solutions of Groups) group contribution method was used to predict water activities in solutions of carbohydrates, polyalcohols and urea. Water activities for the systems water-fructose, water-fructose-urea and water-glucose-urea at 25°C were measured with an electric hygrometer. A set of new ASOG groups was considered and their interaction parameters calculated by numerical non-linear regression of published and measured experimental data. a_w Values predicted by the proposed method agree with experimental data within 0.1–0.9%.     

Prediction of NaCl,nitrate and nitrite contents in minced meat by using a voltammetric electronic tongue and an impedimetric sensor

A method for predicting levels of sodium chloride, sodium nitrite and potassium nitrate in minced meat by using a combination of two different electrochemical methods; namely an electronic tongue (ET) based on pulse voltammetry and electrochemical impedance spectroscopy measurements is proposed here. The measurements with the voltammetric ET were carried out on both saline solutions (brines) and minced meat, whereas the impedimetric sensor was used only in minced meat. The addition of the salts was performed following an experimental design in which a system of three compounds/three levels was established. Multivariate analysis including Cross validation and Partial Least Square (PLS) techniques were applied for data management and prediction models building. A very good prediction of the concentration of chloride was achieved, whereas the prediction for the concentration of nitrate and nitrite can be considered as moderate.     

The effect of sugars on the diffusion of water in starch gels: a pulsed field gradient NMR study

The self-diffusion coefficient of water was measured in starch–sugar–water systems of various compositions. The starch was either waxy maize or potato starch and the sugar was either sucrose or xylose. The diffusion results obtained from sugar solutions (i.e. with a zero polymer concentration) suggested that a free water behaviour should only be expected after a bilayer coverage of the sugar molecule. The presence of sugars was found to decrease considerably the translational mobility of water in starch gels. This reduction was proportional to the sugar concentration in the system but showed little dependence on the type of sugar. An attempt was made to relate the self-diffusion coefficients of water in starch–sugar–water gels to those obtained for the individual binary systems (starch–water and sugar–water). A prediction based on the additive effects of sugar and starch only corresponded with experimental results in dilute systems.     

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.     

SORPTION ISOTHERMS OF TURKISH DELIGHT

Moisture sorption isotherms of Turkish delight were determined using the gravimetric static method of saturated salt solutions at 10, 20 and 30C. Isotherms were found to be of type III, typical of high sugar foods. The effect of temperature on moisture content was not significant (P>0.05). The sorption isotherms exhibited hysteresis at low water activities (a_w < 0.5). At higher water activities the moisture content increased sharply as the temperature was increased, resulting in crossing of the isotherm curves at 0.65 water activity. Six models namely the BET, the GAB, the Halsey, the Henderson, the Chung & Pfost and the Iglesias & Chirife were evaluated to determine the best fit for the experimental data. The GAB and the Iglesias & Chirife models fitted well the data of Turkish delight in the temperature and water activity range investigated. However, the GAB model was not appropriate for the estimation of monolayer value. The Clausius-Clapeyron equation was used to examine the isosteric heats of sorption.     

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%.     

The solubility of limonin,the bitter principle of orange juice

Limonin analyses were made on solutions obtained by equilibrating water at pH 6.3 and pH 3.2 with limonin at temperatures ranging from 0 to 100°C. The results indicated that the increase in the limonin assay with increasing temperature was due to the effect of heat on both the direct solubilisation of limonin and the hydrolysis of limonin to the related hydroxyacid. On storing these solutions at 25°C for several months, the assays from the acidified solutions fell to about the solubility of limonin in unheated solutions equilibrated at 25°C, but the four-fold higher analyses recorded for the neutral solutions indicated that they still contained considerable amounts of the hydroxyacid due to the maintenance of the lactone-hydroxyacid equilibrium. Although sugars and pectins had no detectable effect on the solubilisation of limonin at 25°C, they markedly increased the amount of limonin passing into solution on heating. In addition, they affected both the position of the equilibrium in these solutions on cooling and the rate at which the equilibrium was reached. Moreover, the equilibrium in supersaturated solutions of limonin and its rate of establishment also depended on the methods used for their preparation. These findings are discussed in relation to studies on bitterness in orange juice.