Factors which may influence the determination of autolysis of starter bacteria during cheddar cheese ripening

An investigation of the factors affecting the determination of autolysis of the starter strain Lactococcus lactis subsp. cremoris G11 during Cheddar cheese ripening was undertaken. Autolysis was monitored by determining the activities of intracellular marker enzymes, lactate dehydrogenase (LDH), glucose-6-phosphate dehydrogenase (G6PDH) and post-proline dipeptidyl aminopeptidase (PPDA), in cheeses which were extracted under hypo- and hypertonic conditions. Increased salt-in-moisture levels in the cheese, in the range 0·4-5·0%, were accompanied by increases in the activities of LDH and G6PDH and decreases in the activity of PPDA. The activities of LDH, G6PDH, and in some cases PPDA, increased in cheeses ripened at 4 or 10°C for up to 60 days; thereafter, activities reached a plateau or decreased to various degrees. Addition of sucrose or NaCl to the assay cuvette also affected the activity of all marker enzymes; increasing the concentration of NaCl resulted in increased activity of all enzymes while increasing concentrations of sucrose in the cuvette reduced LDH activity but increased the activities of PPDA and G6PDH. Holding the enzymes prepared from a cell free extract (CFE) for 4 h at 4°C resulted in about 20% decrease in the activities of LDH and PPDA. while in the case of G6PDH a 40% decrease in activity was noted. Addition of a CFE containing the marker enzymes to a cheese-like environment indicated that LDH activity appeared to be the most stable (40% of original activity remained after 500 h at 4°C) while G6PDH or PPDA activities had disappeared after 48 or 24 h, respectively.