A Bacterial Enzymatic Method for Determining Tyrosine in Cheese

Abstract

A rapid quantitative method, specific for free tyrosine in ripened Cheddar cheese, is presented. In this procedure an active bacterial decarboxylase preparation converts free tyrosine to its amine, tyramine, under suitable conditions. A multiple ether extraction pH 10.5 quantitatively recovers both the initial free tyramine and any resulting from decarboxylation. Then from 2d sample of the same cheese not subject to decarboxylation only the initial free tyramim is recovered. Colorimetric analysis of the amine with Million''s reagent preferably; or Folin-Cicocalten''s reagent follows, and through the use of suitable formulas the free tyrosine of cheese, total tyrosine liberated from protein during ripening, and free tyramine can be calculated. Recovery experiments, precautions, and an apparatus designed for the rapid and simultaneous extraction of the tyrosine contents of 10 samples of cheese as tyramine are described and discussed.