Aminotransferase activity of organisms isolated from smear cheeses

SIHUFE G. A.; ZORRILLA S. E.; RUBIOLO A. C.; MCSWEENEY P. L. H.

Córdoba, Argentina

Congreso; Congreso Internacional de Ciencia y Tecnología de los Alimentos; 2006

Agencia Cordoba Ciencia

Flavour development during cheese ripening results from a series of biochemical processes in which the starter cultures provide enzymes. Amino acid catabolism is a major process for flavour formation, especially in cheeses containing only lactic acid bacteria (LAB). The conversion of amino acids to aroma compounds by LAB is usually initiated by a transamination reaction, catalysed by aminotransferases and results in the formation of a -ketoacids, which are then degraded to various aroma compounds. In bacterial surface-ripened cheeses (smear cheeses), flavour is determined primarily by the growth of the surface microflora. However, the enzyme systems of these organisms have not been studied in the same detail as those of LAB. Therefore, the contribution of these smear strains to cheese ripening is less clear. Our objective was to evaluate the aminotransferase activity present in different strains isolated from smear cheeses and to determine their ability to catabolise branched-chain amino acids (BcAA), aromatic amino acids (ArAA) and methionine (a sulphur amino acid). Aminotransferase activities of nine strains originally isolated from Gubbeen, an Irish farmhouse smear-ripened cheese (3 strains of the Microbacterium casei, 3 of Corynebacterium casei and 3 of Corynebacterium mooreparkense), were studied in triplicate. The rate of formation of L-glutamic acid was used to test for aminotransferase activity and the glutamate produced during the reaction was determined by a colorimetric assay using an enzyme assay kit. The amino acids assayed were Leu, Ile, Val (BcAA), Trp, Tyr (ArAA), and Met (a sulphur amino acid). One unit of activity (U) was defined as the activity necessary to release 1 m g of Glu min-1 under the conditions of the assay. The specific activity (u) was defined as U per mg of protein in each cytoplasmic extract. The different strains had low aminotransferase activities on Met as substrate, but all strains had aminotransferase activity on ArAA and BcAA. One strain of Microbacterium casei (DPC 5286) had higher activity on ArAA (particularly Trp); the strains of Corynebacterium mooreparkenese showed high aminotransferase activities on BcAA as substrates and the catabolism was, in general, similar for Leu, Ile and Val. Statistical analysis showed that there were significant differences (p < 0.01) between the enzyme activities of the strains for all the amino acids studied. These results may be useful in elucidating the role of these bacteria in flavour development during the ripening of smear cheeses and indeed lead to a better understanding of cheese ripening.