FACTORS INFLUENCING THE NUTRITIONAL VALUE OF FISH FLOUR: II. AVAILABILITY OF LYSINE AND SULPHUR AMINO ACIDS

Abstract

Measurements of net protein ratio and protein efficiency ratio indicated marked variability in nutritional value of the protein in eight samples of fish flour. The availability of lysine in the samples was examined by in vitro digestion studies, gross protein value determinations, and the dinitrofluorobenzene procedure. One sample, which appeared to be severely heat-damaged, contained unavailable lysine. This sample also contained unavailable methionine, as shown by reduced ability to supplement a methionine-deficient diet, and reduced release of methionine during in vitro digestion with proteolytic enzymes. Another sample also showed reduced ability to supplement a methionine-deficient diet, suggesting that it also contained unavailable sulphur amino acids, although the in vitro release of methionine was not reduced, and the lysine was available.