Rat bioassays for methionine availability in 16 food sources
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Methionine availabilities of 16 test proteins were assessed by comparing ten day rat growth response to the test diets and reference (casein) diets. In a preliminary study, various concentrations of methionine and cystine were fed to determine methionine requirements and effect of excess cystine. Results indicated a methionine requirement of about 550 mg per 100 g diet. Cystine had a sparing affect of 50–55%, i.e., about 300 mg could be used to meet methionine requirements. Further additions of cystine (up to 2.6 times methionine) did not affect rat growth. Methionine availabilities were excellent (88–100%) for 15 of the 16 test foods; only pinto beans (58%) were low, but prior evidence indicates that the poor growth response was due to some factor other than availability.
Key wordsprotein quality amino acids
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