The use ofStreptococcus zymogenes for estimating tryptophan and methionine bioavailability in 17 foods |
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| Authors: | Patricia Wells Frank McDonough C. E. Bodwell Anthony Hitchens |
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| Affiliation: | (1) Agricultural Research Service, Beltsville Human Nutrition Research Center, Energy and Protein Nutrition Laboratory, U.S. Dept. of Agriculture, 20705 Beltsville, MD, U.S.A.;(2) Present address: Food and Drug Administration, HFF 234, 20204 Washington D.C., U.S.A. |
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| Abstract: | As part of a cooperative study assessing amino acid bioavailability and/or protein quality, the provisional method of Boyneet al. (Brit J Nutr 21: 181–206) was used to assay 17 protein sources for methionine and tryptophan availability withS. zymogenes. Pronase was used as the predigesting enzyme. Product composition was found to affect reproducibility. The microbial assay results correlated positively with results from rat growth studies on the same foods (p=0.05), and were generally accurate in identifying products of lower protein quality. Defatting four high-fat products increased microbial values in the methionine assay, but only the chicken franks and the sausage values in the tryptophan assay. Heating non-fat milk increased methionine values slightly. Low values for rolled oats were further reduced by finer grinding. |
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| Keywords: | protein quality tryptophan methionine S. zymogenes |
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