Correlation of Water Activity Data in Whole Tomato Concentrates

It is shown that water activity (a_w) data in whole tomato concentrates of varying total solids content may be well correlated using a simple equation derived from knowledge of the a_w lowering behavior of nonelectrolytes. The proposed equation has practical value because it allows a_w, prediction in tomato concentrates (in the a_w range of most practical interest) from measurement of the °Brix value.     

A New Model for Describing the Water Sorption Isotherm of Foods

This work investigated the applicability in the food area of a new sorption equation recently developed by Ferro Fontán et al. (1982). The equation may be written, 1n (γ/a_w) =α (m)^-r, where, γ, α and r are parameters to be determined, m is the moisture content, and a_w is water activity. It was found that the three parameter equation is able to describe the water sorption isotherm of 18 different foods in an extensive range of a_w (up to about 0.95) with only 2–4% error (average) in the predicted moisture contents. Foods examined comprised, among other, oilseeds, starchy foods, and proteins.     

Kinetics of Water Uptake by Food Powders

The water uptake by several food materials that included animal and vegetable proteins and starch materials was studied. The amount q of water taken up by a sample powder during time t was described by the equation q = Qt/(B + t), where Q is the total water uptake of equilibrium and B is the time required to sorb Q/2. The rate of water uptake was proportional to the square of the amount of water that must still be absorbed to reach equilibrium. A specific rate constant for the process was calculated as (BQ)^?1.     

Effect of Heat Treatment on Sorption Isotherms and Solubility of Flour and Protein Isolates from Bean Phaseolus vulgaris

The effect of heating at 50, 70 or 90°C and low moisture contents on water sorption behavior (above about 0.65 water activity) and nitrogen solubility of bean flour and protein isolates, was investigated. The results suggested that relative water sorption changes, in the range studied, may not be the most adequate indicators of nitrogen solubility changes in “dry”/“moist” heated protein products. This is so because heated samples may undergo very important changes in nitrogen solubility while having experienced relatively little modifications in water sorption capacity.