Composition and nutritive value of yeast biomass and yeast protein concentrates

Yeast biomass (Saccharomyces sp.) produced in local breweries as a by-product was utilized in this study. Percent proximate composition, amino acid composition, and protein nutritive value were determined for the yeast cell biomass (YC), a sodium perchlorate extracted and isoelectrically precipitated protein concentrate (P-PC), and a sodium trimetaphosphate treated extract followed by isoelectrical precipitation (TMP-PC). Protein concentrates averaged 75% protein as compared to 48.5% in the yeast biomass. Precipitation of the protein in the presence of either sodium perchlorate or sodium trimetaphosphate was reduced to 71% and 51% of the cell RNA content, respectively. Protein nutritive value was 70% of casein when measured by the protein efficiency ratio (PER), and over 90% of casein when net protein utilization (NPUa) was the criteria of evaluation.