Blood amino acid studies in the weanling rat on diets containing raw and autoclaved soyabean.

Weanling male rats were fed diets containing 1C% protein from
raw or autoclaved soybean for 7 days. Levels of plasma lysine,
methionine, threonine and tryptophan were determined and plasma amino
acid (PAA) scores were calculated. The PAA score indicated that
aethionine is the limiting amino acid in soybean. Threonine and
tryptophan levels were low in the plague of rats fed raw soybean, bat
increased markedly on feeding autoclaved soybean. Supplementation of
raw soybean diet withL-Rethionine resulted in a highly significant
increase in the level of methionine in the plasma indicating that the
inhibitors present in the raw soybean do not affect the availability
of added methionine. Supplementation of autoclaved soytean diet with
L-methionine, resulted in a marked increase in the plasma methionine
levels but caused a significant lowering of the threonine level.
Methionine supplementation markedly increased the protein efficiency
ratio (PER) of autoclaved soybean, but addition of threonine along
with methionine did not result in any further improvement in the PER,
although the threonine level in the blood increased. The results
indicated that, apart from threonine, some other amino acid(s) may be
limiting in soybean proteins.