Studies on Assay for Amino Acids in Foods:Assay of Tyrosine

概要

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Tyrosine is partially destroyed during hydrolysis of foods, especially in the presence of carbohydrate, and this fact induces incorrect informations on tyrosine content in foods. For the purpose to establish the favorable condition for tyrosine assay, comparison of assay values obtained by chemical and microbiological determinations of various acid and alkali hydrolyzates of foods was made. As a result it was found that hydrolysis at 120°C for 15 hours with 4N-NaOH or HCl, and chemical assay with 1-nitroso-2-naphthol gave highest assay value. Alkali hydrolysis was suitable for foods containing much amount of carbohydrate, and acid hydrolysis for that containing less amount of carbohydrate. In alkali hydrolyzate of foods, a tyrosine derivative was produced beside tyrosine. Although this derivative also gave red color with nitrosonaphthol, its optical density was confirmed to be equal to that of tyrosine. Therefore, the occurrence of this derivative does not obstruct the chemical assay of tyrosine in alkali hydrolyzate of foods.
公益社団法人日本栄養・食糧学会の論文