Effect of Carbohydrates and Heat on the Amino Acid Composition and Chemically Available Lysine Content of Casein

Casein, casein‐starch, casein‐sucrose, and casein‐glucose mixtures were heated under conditions modeling storage, autoclaving, baking/broiling and charring (37–300°C). Losses in total and chemically available lysine content were measured by fluorodinitrobenzene (FDNB) and dye‐binding methods. The lysine and arginine content decreased up to 99%. Changes in amino acid profiles were accompanied by the appearance of at least five new ninhydrin‐positive compounds. The relative potencies of the three carbohydrates effecting these changes were different at the four temperatures studied. The available lysine contents of the samples measured by the two independent methods were identical within experimental error. The results show different susceptibilities of casein to heat‐ induced damage in the presence of different carbohydrates.