An investigation of the autolytic properties of three lactococcal strains during cheese ripening

Cheddar cheeses were manufactured using Lactococcus lactis ssp. cremoris AM2 (a non-bitter strain), HP (a bitter strain) or 303 (a commercial starter). Lysis was monitored in the cheese at various intervals over a 10-week ripening period by measuring the activities of intracellular marker enzymes [lactate dehydrogenase (LDH), glucose-6-phosphate dehydrogenase (G6PDH) and post-proline dipeptidyl aminopeptidase (Pep X)] in the cheese juice. On day 1 of ripening, starter cell counts in cheeses manufactured using strain HP or 303 were in the range 10⁹-10¹⁰ cfu g^-1 cheese compared to 10⁸ for AM2. Viability of starter strains during ripening decreased in the order: 303 > HP > > AM2. Autolysis of the different strains, as indicated by the release of the marker enzymes, during cheese ripening decreased in the order: AM2 > > 303 > HP. The degree of secondary proteolysis followed a similar trend to autolysis. Neither NSLAB numbers nor inter-strain variations in the specific activity of intracellular marker enzymes appeared to influence the activity of marker enzymes in Cheddar cheese during a 10-week ripening period.