Microbiological assay of protein quality with <i>Tetrahymena pyriformis</i> W

Abstract

I . A microbiological assay using the protozoan Tetrahymena pyriformis W for measurement of available lysine, methionine, arginine and histidine is described and the application of the assay is illustrated by values for available amino acid content of a wide range of animal and vegetable protein sources. z. Comparison with values reported by Boyne, Carpenter & Woodham (1961) and Miller, Carpenter & Milner (1965) for animal protein sources showed Tetrahyrnena estimates of available lysine to be similar to those obtained by the fluorodinitrobenzene (FDNB) method of Carpenter (1960) for samples with higher available lysine content (c. 8 8/16 g N) but lower than FDNB values for samples with lower available lysine content. 3. Tetrahymena assays of available lysine in groundnut meals and soya-bean meals showed little variation between samples of one type of oilseed meal. The values obtained also suggest that modern commercial processing has little or no effect on lysine availability in groundnut and soya-bean meals. There was considerable variation between samples in the available lysine content of cottonseed meals, possibly due to binding of lysine by the gossypol present in these meals. 4 . There also appeared to be considerable variation in the available lysine and methionine content of different samples of the same type of cereal.