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The abilities of picric, sulfosalicylic (SSA), tricbloroacetic (TCA), and tungstic acids to precipitate a partial hydrolysate of egg albumin and several proteins were examined. After precipitation of the hydrolysate with SSA, TCA, and tungstic acid respectively, it was found that 88%, 79%, and 69% of the nitrogen remained in solution. The average size of the peptides in the supernatants varied from 330 to 380 daltons. The ability to precipitate native proteins varied with the precipitant and the protein. Tungstic acid precipitated both bovine serum albumin and p-lactoglobulin completely at low concentration (0.5% final concentration, w/v). Bovine serum albumin was precipitated by 3% TCA or SSA but, p-lactoglobulin was not completely precipitated until the concentrations had been increased to 10% and 20%, respectively. Pretreating p-lactoglobulin with sodium dodecylsulfate increased the amount precipitated by SSA and TCA.

Black beans stored at 30" or 40°C and 80% relative humidity showed marked increases in firmness and decreases in in vitro digestibility of proteins. Changes in these properties were small when beans were stored at 5°C and 50% relative humidity. The adverse effects of poor storage conditions could be practically eliminated by soaking beans in salt solutions instead of water. The changes in firmness and digestibility were accompanied by changes in the detectable concentrations of tannins and phytates. Protein digestibility appears to be reduced by interactions between protein and tannins, especially high molecular weight tannins. Concentration of these tannins is affected by polyphenol oxidase activity. Firmness increased and protein digestibility decreased as the phytic acid content decreased.

Gelled plastein reaction products were prepared by treating concentrated peptic hydrolysates of egg albumin with pepsin, cY-chymotrypsin, and papain. The relative firmness of these homogeneous gels was determined by comparing force-distance curves obtained from puncture tests made with the lnstron Universal Testing Machine. The effects of the choice of enzyme and degree of substrate hydrolysis on the plastein yield (increase in 10% Trichloroacetic acid precipitable material) and water solubility were investigated. Electrophoresis of plastein products in the presence of sodium dodecyl sulfate (SDS) indicated that no high molecular weight, protein-like material was produced by the plastein reaction. It is suggested that plastein reactions lead to the formation of insoluble peptide aggregates. These aggregates are thought to be held together by noncovalent bonds rather than by covalent, peptide bonds, as has been reported previously.