pH changes in buffers and foods during freezing and subsequent storage

Changes in pH and salt composition of the liquid phase of frozen buffer solutions (sodium and potassium phosphates, with added chlorides) and foods (milk, meats, fish, and vegetables) have been determined to obtain information on physicochemical changes induced by freezing. Results, obtained by using glass and calomel electrodes especially designed for operation at subfreezing temperatures as well as by chemical analysis, showed that the pH and salt composition of the liquid phase changed markedly during freezing and subsequent frozen storage because of the precipitation of salts which had become supersaturated by the formation of ice. These pH and composition changes depended on supersaturation, protein-salt interactions, and enzymatic activity. A comparison was made between the observed physicochemical changes and some of the quality changes known to occur in frozen foods.