Nutritional quality of a spun soya-bean protein: Comparison of biological and microbiological tests

A commercial spun soya-bean protein that had been subjected to mild alkali treatment in its manufacture, and the protein isolate from which it had been made, were evaluated in biological and microbiological tests. When diets were givenad lib. in tests with rats, growth was better on the parent protein; but with equal, restricted dietary intakes there was no difference between the two protein sources. The kidneys of all the rats appeared normal on histological examination and showed no signs of nephrocytomegalia, which has been found in the kidneys of rats given soya protein subjected to severe alkali treatment. Similarly in growth tests with chicks, there was no difference between the two proteins and it was concluded that the manufacturing process did not impair the nutritional quality of the spun protein. In microbiological assay tests withStreptococcus zymogenes, the available methionine of the alkali-treated material was consistently lower by about 20%. But when pronase was substituted for the papain normally used in the assay procedure there was no difference between the preparations; the methionine appeared fully available. The lower values following papain predigestion probably indicated a real though small difference in rate of proteolysis but this was clearly not significant in relation to biological availability for rats and chicks.