Chemical composition of Candida utilis and the biological quality of the yeast protein

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Abstract
The chemical composition (moisture, ash, protein and non‐protein N, amino acids, ether extract, crude fibre, Ca, P, Fe) and biological quality (protein efficiency ratio and available lysine) were investigated in two batches of Candida utilis (Torula yeast). The samples (S1 and S2) were collected from a local factory. S2 was sterilised before drying. Protein, mineral and B‐complex vitamin contents were comparatively high. Amino‐acid analysis showed a high content of lysine and threonine, but a deficiency in sulphur amino acids. The biological quality measured as the protein efficiency ratio (p.e.r.) and available lysine gave values of 1.80 ± 0.05 and 6.6 g/100g of crude protein, respectively, in S1. These are higher than values reported in the literature. Sterilisation (S2) and storage for 1 year (S1(a)) significantly reduced the biological quality of the protein (p.e.r. 1.15 ± 0.12 and 1.34 ± 0.07, respectively). Supplementation of C. utilis with 0.3% DL‐methionine increased the p.e.r. value to 2.77 ± 0.03, close to that of casein. C. utilis appears to be a valuable material for human diets because of the high content and satisfactory quality of its protein and other nutrients.