Chemical composition and biological value of proteins of the yeast Yarrowia lipolytica growing on industrial glycerol

The aim of this study was to evaluate the chemical composition and biological value of proteins from the yeast, Yarrowia lipolytica, after cultivation on glycerol, a waste product obtained in the production of biofuel from rapeseed. In the tested material we determined moisture, crude protein, ether extract, nitrogen-free extract (NFE), ash, calcium, phosphorus, cadmium, mercury, arsenic, amino acids and fatty acids. The biological value of Y. lipolytica and Saccharomyces cerevisiae proteins was determined with laboratory rats by two methods: the growth method (protein efficiency ratio standardized for casein, PERstand; net protein retention, NPR) and the Thomas -Mitchell method (biological value, BV; true digestibility, TD). The protein content of Y. lipolytica [467 g kg(-1) dry matter (DM)] was similar to that of S. cerevisiae (479 g kg(-1) DM). Of particular interest was the almost 30-times higher crude fat content in Y. lipolytica (200 g kg(-1) DM) than in S. cerevisiae (6.7 g kg(-1) DM). Yarrowica lipolytica cells accumulated substantial amount of fat in which more than 90% of fatty acids were unsaturated fatty acids with a considerable share of polyunsaturated fatty acids (34%). The low share of sulfur amino acid of Y. lipolytica (2.05 g 16g(-1) N) and S. cerevisiae (2.32 g 16g(-1) N) limited the nutritional value of the protein of the studied yeast. The biological value of proteins as assessed by the growth method (PER, NPR) did not differ between the two yeast species. Finally, Y. lipolytica was a rich source of highly digestible ether extract (over 57%).