STUDIES ON LACTIC-ACID ISOMERS IN PECORINO-ROMANO CHEESE BY MEANS OF RADIOTRACERS

The evolution of microflora, carbohydrates and lactic acid isomers was studied in Pecorino Romano cheese, and the isomerization of L(+) and D(-) lactic acid was examined during the ripening period by means of C -14 labelled compounds. Only small quantities of D(-) lactic acid were found by enzymatic analysis, compared to the L(+) isomer. The former continued increasing until 30 days, while the L(+) form decreased afte r the first days of ripening. The experiments carried out by means of radiotracers, indicated that both isomeric forms of lactic acid are su bject to isomerization, which means that also the D(-) form is transfo rmed into L(+) isomer. A quite high number of non-starter bacteria, su ch as yeasts, propionic acid bacteria and Micrococcaceae, were observe d inside and outside the cheese. The linear relationship between micro bial count and the metabolic compounds was determined, and significant coefficients were found confirming that non-starter microflora could be involved in the transformation of these metabolic compounds.