Protein quality of feeding-stuffs. 4. Progress report on collaborative studies on the microbiological assay of available amino acids.

Abstract

1. Samples of whale, meat, fish, groundnut and soya-bean meals and skim-milk powders were assayed microbiologically with Tetrahymena pyriformis W and Streptococcus zymogenes for available methionine and available lysine.2. Detailed collaborative studies on the assay of available methionine with Strep. zymogenes were conducted on the effects of dry- or wet-grinding the test meals, the use of crude or purified papain for predigesting the ground meals and the use of optical density or titratable acidity as criteria of bacterial growth response.3. Wide differences were observed in the available methionine and available lysine contents of a variety of meals in the preliminary studies, with a promising measure of interlaboratory agreement in the assay of available methionine with Strep. zymogenes.4. As a result of detailed collaborative studies a provisional method is proposed for the assay of available methione with Strep. zymogenes, adopting dry-grinding and predigestion with an agreed level of papain in the preparation of the meals. No general recommendation could be offered on the comparative merits of optical density and titratable acidity as criteria of bacterial growth response.