Protein Quality and “Available Lysine” in Animal Products

Abstract

Nutritional damage to animal products during processing is not always reflected in amino-acid assays of acid hydrolysates of these materials (Bissett and Tarr, 1954). In the present study a biological measure of protein quality has been compared with values from a chemical method designed to estimate “available lysine,” on the basis that it is thought to be the ε-NH2 group of lysine that reacts to form a nutritionally-unavailable complex when intact proteins are damaged. The biological test was a modification (Carpenter, Ellinger and Shrimpton, 1955) of the “gross protein values” (G.P.V.) method using the response of chicks when 3% of protein from test materials supplements a basal “cereal and vitamin” mixture contributing 8% protein (Heiman, Carver and Cook, 1939). The chemical method followed that used to study free-NH2 groups in purified proteins by their reaction with 2,4-dinitrofluorobenzene (DNFB) to give stable dinitrophenyl- (DNP-) compounds (Sanger, 1945). Suspensions of test material …