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Component interactions in the sucrose-starch-water system were investigated. Starch, sucrose, a mechanical starch:sucrose mixture and four powders obtained by freeze drying dilute aqueous mixtures were equilibrated to a, ranging from 0.33-0.93. Both raw and gelatinized starch were included. Sucrose-starch interaction was determined by measuring the reduction in water sorption as compared to theoretical. Only the freezedried mixtures showed interaction. Interacted sucrose, calculated as the sucrose that did not bind water, (1) decreased from a maximum at 0.86 a, to zero at 0.936 a,, and (2) rose sharply with increasing sucrose-starch ratio to a maximum at a ratio of 0.4 and decreased to zero with further increase in ratio to 1.5. More sucrose interacted with gelatinized than raw starch.

The objective of this work was to determine the processing conditions responsible for suspension stability of Illinois soybean beverage and to elucidate the role of lipid in this stability. Stability was determined by visual and objective means after 5 days quiescent storage at 1°C. Pressure and temperature of first and second homogenization, formulation, lipid component and accelerated settling were studied. Homogenization pressure must be such that the sum of the two pressures must be at least 5000 psi and the minimum temperature of one of the two homogenizations must be 82°C. Free and, especially, bound lipid are necessary for stability. The hypothesis that stability is promoted by formation of a lipid-protein complex was further demonstrated by centrifugation and film formation studies. Formulation plays a minor role in stability.

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Sorption isotherm dz ta are obtained by instrumental determination of water activity at a known moisture content or determination of moisture content after equilibration against a saturated salt solution. The latter method is t impler and the salt solutions are primary standards. However, the equilibration takes a long time, one to ten weeks, depending upon focd composition. Thus, the objective of this work was to devise a method that retains the saturated salt solution but accelerates the rate of equilibration. In an equilibration environment between a food product and a saturated salt slurry, the driving force is the difference in vapor pressure; therefore the faster the vapor space reaches equilibrium with the saturated salt slurry, the quicker the maximum driving force for water absorption will be applied to the sampll:. It was felt that a reduction in the size of the usual large desiccate r to a single sample size would provide the necessary area to volume ratio. The vessel chosen was a small plastic chamber (65 mm/5:; mm). In this chamber, the surface area to vapor volume ratio was 0.3101 as compared to 0.0335 for the standard desiccator. The sample was contained in a standard aluminum weighing tray modified by removing a 44 mm diameter circular section from the bottom. This was replaced with a 47 mm diameter circle of Whatman 140. 1 quantitative filter paper to support the sample and at the srme time allow transmission of moisture. This would allow water inolecules to travel in a straight line and thus the shortest distance between the saturated salt slurry and the sample. This small vessel with a single sample supported on a filter paper wilI be referred to :IS a Proximity Equilibration Cell (PEC). Using this technique, it wa; found that a 2/mm deep sample of corn starch required only 6 da;rs for complete equilibration, as compared to 21 days for the conventional desiccator. Thus, the PEC satisfied the objective by reducing time by 70%. In making comparisons with the same salts in conventional and the PEC, it was noted that the end point was higher in the latter. Evidently, absorption in case of the conventional llesiccator was so slow at the end that no weight gain could be detected in 24 hr but equilibrium had not yet been attained. In contrasl, the PEC equilibrated so rapidly that it allowed a closer evaluation o i true equilibrium. INTRODUCTIONTHE MOISTURI: SORPTION isotherm relates moisture content of material to its water activity (a,) at a given temperature. In ord,:r to obtain a given point, a sample is equilibrated agair st a solution of constant and known a,,, and its moisture I:ontent determined. The primary standard for a, equilibration is a saturated salt solution; the National Bureau of Standards (Greenspan, 1977) published a list of 28 salts coverirlg the a, range 0.03-0.98.The apparatus used for this equilibration is a large desiccator that holds I he standard solution in place of desiccant; a number of disltes holding the material rest on a support some distance ab ave. the solution. It ...