Nutritive value of processed Saccharomyces cerevisiae, Scenedesmus obliquus and Spirulina platensis as measured by protein synthesis in vitro in rat skeletal muscle

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Abstract
Rats were fed for six consecutive days on a diet containing the protein sources under test at a protein level of 20%. Protein synthesis by skeletal muscle ribosomes was measured in vitro. Synthetic activity was estimated per unit ribosomal RNA and per g of wet weight of muscle. In separate experiments the nitrogen efficiency ratio (n.e.r.) of the protein sources was determined after 21 days feeding at a 10% protein level.As measured by protein synthesis the nutritional quality of lyophilised baker's yeast Saccharomyces cerevisiae increased after mechanical disintegration. A further improvement was achieved by feeding yeast protein concentrates.Judged by these determinations the nutritional quality of the three yeast preparations was higher than that of the low‐quality protein, wheat gluten but did not reach the level of the high‐quality protein, casein supplemented with methionine.The metabolic utilisation of spray‐dried microalga Scenedesmus obliquus increased after mechanical disintegration from a value similar to that of wheat gluten to the level of methionine‐supplemented casein.Lyophilised Spirulina platensis had a nutritional quality between that of wheat gluten and casein supplemented with methionine.Addition of the limiting amino acid methionine to air‐dried baker's yeast or drum‐dried Scenedesmus obliquus and Spirulina platensis stimulated the metabolic utilisation of the micro‐organisms.Supplementation of the diet with methionine increased the nitrogen efficiency ratio of air‐dried yeast and of drum‐dried Scenedesmus obliquus but had no effect on drum‐dried Spirulina platensis. The ratios were significantly lower than those of casein supplemented with methionine.There was no difference in the nitrogen efficiency ratio between disintegrated yeast and yeast protein concentrate but the ratio of both was higher than that obtained with lyophilised yeast. The ratio was similar to that of casein without the addition of methionine.