The Alanine, Cystine, Glycine and Serine Content of Meat

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Abstract
The alanine, cystine, glycine and serine content of 18 samples of beef, lamb, pork and veal muscle cuts and beef organs have been determined by microbiological assay procedures specially modified for this purpose. Where possible, values have been compared with reports in the literature. Cystine, glycine and serine, with average values of 1.1, 5.0 and 5.2%, respectively, were each determined with two microorganisms, which gave results in good agreement with each other in repeated analyses. Alanine, determined with one microorganism, gave an average value of 6.4%. Depending on the amino acid concerned, certain of the beef organs gave higher values than the muscle meats. Tween 80 (polyoxyethylene sorbitan monooleate) was added to all assay media at a level of 0.005% by volume. Addition of this detergent eliminated a lag from the alanine standard curve and lowered the blank titration values, removed the depression of growth for L. mesenteroides at the higher levels of cystine, eliminated drifts with L. casei in serine assays and increased the recovery of serine with L. delbrueckii from 94 to 98%. In addition to the above, Tween 80 produced a general stabilizing effect in all assays, resulting in less variation and greater reproducibility of assay values.