Evaluation of commercial adjuncts for use in cheese ripening: 1. Enzymatic activities and autolytic properties of freeze-shocked adjuncts in buffer system

Eight strains of Lb. helveticus and 7 strains of Lb. casei adjunct cultures were compared according to intracellular aminopeptidase and dipeptidyl-aminopeptidase activities using synthetic p-nitroanilides derivatives of amino acids and dipeptides. Esterolytic activity was measured by using p- and o-nitrophenyl derivatives of fatty acids. The autolytic properties of the cells and their intracellular peptidase and esterase release were also evaluated. Lactobacilli showed different aminopeptidase, dipeptidyl-aminopeptidase and esterolytic activities which were species- and strain-specific. Among the adjuncts tested, Lb. helveticus I, G, and M, and Lb. caseiC had high enzymatic potentials. Their specific activities for lysine aminopeptidase varied from 5 to 10; while the level of esterase activity on p-nitrophenyl caproate ranged from 0.6 to 2.0. The release of these enzymes during autolysis in buffer system ranged from 60 to 80% after incubation at 30 degrees C for 48 h. Lb. casei A, E and Lb. helveticus J exhibited high enzyme activity but their rate of autolysis was low (2 to 20%). This study demonstrates a means to classify adjunct cultures according to their levels of autolysis, enzyme activity, and rate of enzyme release.