THERMOINDUCIBLE LYSIS IN LACTOCOCCUS-LACTIS SUBSP CREMORIS SK110 - IMPLICATIONS FOR CHEESE RIPENING

In recent years, the thermoinducible lysis in lactococci have received much attention as an important characteristic of starter cultures. Th e thermolytic response, observed after subjecting a culture of Lactoco ccus lactis subsp. cremoris SK110 for a period of 2.5 h to a temperatu re increase from 30 to 40 degrees C during the exponential phase of th e growth, resulted in the induction of a prophage in the cells. Electr on microscopy showed isometric phages with an average head size of 55 nm in the induced culture. The key physiological parameters for the th ermo-inducible lysis of SK110 cells were characterized. The sensitivit y of cells to thermo-inducible lysis was shown to be dependent of the growth rate and the pH. The highest thermolytic response was found at near neutral pH values and at high growth rates. The thermolytic respo nse SK110 cells resulted in the release of intracellular enzymes, as m onitored for aminopeptidase, PepN, X-prolyl-dipeptidyl aminopeptidase, PepXP and L-lactate-dehydrogenase. When strain SK110 was used as a st arter culture for the manufacture of Gouda cheese, a significant incre ase in the level of free amino acids was measured after six weeks of r ipening when a temperature shock was used during the cheesemaking proc ess. This indicates that lysis of the starter bacteria plays a signifi cant role in cheese ripening and, moreover, that temperature-induced l ysis of lactococcal strains is a valuable method for affecting the rip ening of cheese. (C) 1998 Elsevier Science Ltd. All rights reserved.