Water Activity – Concentration Models for Solutions of Sugars, Salts and Acids

Abstract

A semi-empirical model of water activity changes due to solute concentrations increase in solutions of electrolytes and nonelectrolytes was developed based on an extension of Raoult's law. Comparisons between predicted and observed a, data for a variety of sugars, salts and acids indicated the proposed model fitted the a,,, data with accuracy to ~0.001 a, up to 4-14 molalities depending upon the solutes. Percent weight concentrations of some solutes for various a,,, values at 25°C were presented for practical applications. INTRODUCTIONIT HAS BEEN RECOGNIZED that both water activity (a,,,) and pH are important indices in the control of food stability and in the formulation of intermediate moisture foods (Rockland and Beuchat, 1987;Rockland and Stewart, 1981). The a, values are between 0 and 1, and the desired accuracy of a,,, measurements and prediction is in the range of + 0.01 a, (Troller and Christian, 1978).Various sugars, salts and acids may be added to adjust the a,,, and pH in food product development. Some of those compounds are also solute components in cellular food materials. The removal of water by drying, evaporation, freezing, and membrane concentration will result in increased solute concentration in the final food products. Therefore, a knowledge of a, in concentrated solutions is important in food process development and in a better understanding of how food components interact with water in food systems.The objectives of this paper were: (1) to develop a model

Development of a validated model to describe the individual and combined water activity depressing effects of water soluble salt, sugar and fat replacers

“…Most of the empirical models found in literature utilize the linear relationship between a w and molality (moles/kg solvent) (Favetto and Chirife, 1985;Chen, 1989;Roa and Tapia, 1998) or mole fraction (Ross, 1975;Ferro Fontan et al, 1981). This implies that the molecular weight must be well defined for one to use these models.…”

“…To date several studies and both empirical and mechanistic models have been developed to relate a w with the concentration of aqueous binary solutions (Ross, 1975;Chirife et al, 1980;Favetto and Chirife, 1985;Chen, 1989;Caurie, 1986;Norrish, 1966) or aqueous multi-component mixtures of various solutes including simple salt and sugar replacers (Ross, 1975;Chuang and Toledo, 1976;Ferro Fontan et al, 1981;Roa and Tapia, 1998;Velezmoro et al, 2000;Caurie, 2005). Reviews on the several approaches that have been made to correlate a w in aqueous solutions (electrolytic and non-electrolytic) and food are given by Cazier and Gekus (2001).…”

Effect of naturally occurring antimicrobials and chemical preservatives on the growth of Aspergillus Parasiticus

“…It was observed that the organism grew well in PDA plates formulated with KCl media. The PDA systems were prepared with 1.2% of KCl as prescribed by Chen (1989) to achieve 0.99 a w , and the media was autoclaved, cooled and acidified with 0.1 N HCl to adjust the pH to the desired level. The sterilized agar solutions were aseptically divided and required quantity of every antimicrobial agent was added and thoroughly mixed before being poured into sterile glass Petri plates.…”

Predicting the initial freezing point and water activity of meat products from composition data

“…The water activity of a non-ideal sodium chloride solution a w;NaCl , follows from the fundamental Pitzer equation, for which Chen (1989) gives a convenient, but accurate approximation:…”

“…Hence, we have extended existing models of freezing point predictions with the relationship for the non-ideal contribution of NaCl to the water activity. This relationship is the approximation of Chen (1989) of the more fundamental Pitzer equation, which predicts the water activity of concentrated NaCl solutions.…”