The objective of this study was to investigate the lysis of a highly autolytic strain of Lactococcus lactis ssp. cremoris AM2 in a model cheese made from concentrated ultrafiltered milk. From the same initial ultrafiltered retentate inoculated with L. lactis AM2, 5 cheeses were made by the addition of rennet at different pH values (6.6, 6.2, 5.8, 5.4, and 5.2). Lysis was monitored by measurement of the release of lactate dehydrogenase, an intracellular marker enzyme, and by immunodetection of intracellular proteins with species-specific antibodies. Confocal scanning laser microscopy (CSLM) was used to investigate the cheese microstructure by staining for protein and fat. Dual staining with a bacterial viability kit with CSLM was performed to reveal the integrity and localization of the bacterial cells. Levels of soluble calcium significantly increased when the pH at which the rennet was added decreased. In cheese renneted at pH 6.6, CSLM revealed an open porous structure containing a dense protein network with fat globules of different sizes distributed in the aqueous phase. In cheese renneted at pH 5.2, the protein network was homogeneous, with a less dense protein network, and an even distribution of fat globules. On d 1, bacterial cells were organized into colonies in cheese renneted at pH 6.6, whereas in ch
