Autolysis of Lactobacilli during Cheddar Cheese Ripening

Experiments were undertaken to determine whether mesophilic lactobacilli undergo autolysis during Cheddar cheese ripening. Intracellular marker enzymes (IME), including D-lactate dehydrogenase, prolinase and a proline iminopeptidase, specific to these lactobacilli, were identified to distinguish lysis of the lactobacilli from that of the starter lactococci. Cheese was manufactured with addition of single strains of mesophilic lactobacilli and Lactobacillus helveticus DPC 4571. During ripening, the numbers of mesophilic lactobacilli remained high in all cheeses, but the numbers of strain 4571 decreased. The IMEs of the mesophilic lactobacilli could not be detected in the cheese juice and the indicators of proteolysis were similar to that of the control cheese. In the cheese made with the thermophilic strain DPC 4571, two IMEs, D-LDH and proline iminopeptidase, were detected in the cheese and the indicators of proteolysis were increased. It was concluded that mesophilic lactobacilli do not autolyse during cheese ripening, but strain 4571 did and that the release of intracellular enzymes influenced proteolysis. When cheese was made commercially with strain 4571, the IMEs were detected in the experimental cheese, indicators of proteolysis were increased and the cheese had an improved flavour, relative to a control cheese. This suggests that there is a correlation between lysis of Lb. helveticus, increased proteolysis and improved flavour.