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Rennet whey protein concentrates have excellent nutritional properties, but their use in fluid food systems is impaired by the poor heat stability of the protein. Heating whey protein concentrated solutions at neutral pH caused up to 70% losses in solubility. In the absence of added calcium, protein coagulation occurred. near the iso-electric zone whereas in the presence of .03 M calcium chloride, similar protein coagulation occurred in the whole pH range (pH 2 to pH 12). Tryptic hydrolysis of the protein increased the heat stability of whey protein concentrates considerably.

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Use of soy protein in a complex fluid food model containing carbohydrate, fat, minerals and 8-10% protein was investigated. Soy protein at this concentration yielded a product that gelified upon heating. Gelation was inhibited if the protein was previously hydrolyzed utilizing food grade proteases. Removal of the high-molecular weight fraction of the hydrolysate by precipitation with calcium further helped to decrease viscosity. Bitterness was reduced without affecting viscosity, through elimination of small peptides and free amino acids by ultrafiltration. Stable and long shelf-life samples of the model could be manufactured if the proteolytic process was carefully controlled in order to avoid losing the stabilization of the emulsion by the soy protein. Nutritional value of the hydrolysate was higher than that of the isolate used.

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