Liberation of lysine by acid and enzymes from heated lysine-glucose mixture.

Studies on the formation of humin in protein hydrolysates have demonstrated that heating causes a reaction between carbohydrates and certain amino acids (l-3). This reaction, often referred to as the Maillard reaction, has significance in connection with the development of brown color during the processing of foods. Further, this reaction appears to have nutritional importance, since recently it has been shown (4, 5) that heating reducing sugars in the presence of amino acids causes the latter to become nutritionally unavailable to chicks and microorganisms. Indeed, Patton et al. (6) have suggested that the decreased availability to chicks and microorganisms of lysine in heat-damaged soy bean oil meal (7, 8) is a result of this type of reaction. Riesen et al. (8) and Clandinin (9) have shown that the liberation of lysine from heat-damaged protein materials by enzymatic hydrolysis is much lower than by acid hydrolysis. These workers suggest that values obtained by enzymatic hydrolysis give a more reliable index of the nutritive value of heat-treated protein materials than do those by acid hydrolysis. The present study was undertaken to determine whether or not the heating of a lysine-glucose mixture in an autoclave for different periods of time affects the liberation of lysine by acid and enzymatic hydrolysis in a manner similar to that reported (8, 9).