Nutritional and toxicological evaluation of yeast (Saccharomyces cerevisiae) biomass and a yeast protein concentrate

Abstract

Brewer's yeast was prepared by alkaline treatment for debittering, cell wall rupture and dehydration by spray drying. Yeast protein concentrate was prepared by centrifugation of the ruptured cell suspension, treatment of the supernatant with sodium perchlorate, precipitation of the protein at isoelectric pH (4.2) and neutralisation of the isoelectric protein to pH 6.5 with sodium hydroxide, prior to lyophylisation. Chemical characterisation was performed on the biomass and protein concentrate. Amino acid scores were 98.1 and 87.2% for the whole biomass and protein concentrate respectively, based on available lysine and compared with the FAO/WHO/UNU reference standard. The growth-promoting property of the yeast biomass protein was roughly 85% of casein and was significantly better than for the yeast protein concentrate. No difference in growth was found between 15 and 30% dietary protein for all three sources, ie casein, whole yeast biomass and yeast protein concentrate. When tested for subchronical toxicity at 15 and 30% protein concentration, no evidence of toxicity was found for the whole yeast biomass, compared with casein, after 45 and 90 days of feeding. Retarded growth and discrete liver steatosis were observed in rats fed the yeast protein concentrate at both dietary levels. © 2000 Society of Chemical Industry