A chemical and nutritional evaluation of yeasts and bacteria as dietary protein sources for rats and pigs

Abstract

Abstract Eight commercial single‐cell protein preparations grown on hydrocarbon substrates, and which comprised six yeast and two bacterial samples, were analysed for amino acid, nucleic acid and hexosamine content. Amino acid analysis indicated that in all eight samples the sulphur‐containing amino acids were likely to be limiting for both rats and pigs. In experiments with rats the six yeast SCP samples gave biological values between 55 and 62, with true N‐digestibilities between 79 and 93%. The chemical scores, based on the sulphur amino acid requirement of the rat (4.2 g/16 g N), ranged from 50 to 67. The two bacterial SCP samples gave lower biological values (42 and 52), with true N‐digestibilities of 90 and 91%, and the chemical score of each bacterial SCP was 57. Supplementation with methionine improved the biological value of all eight samples. In experiments with pigs three yeasts were evaluated and gave apparent biological values between 43 and 47. Two of the yeasts were supplemented with methionine and in both cases this led to improvement in biological value.