Growth of Debaryomyces hansenii on a bacterial surface-ripened soft cheese

Experimental cheeses were prepared in triplicate from pasteurized milk inoc ulated with Debaryomyces hansenii under aseptic conditions. Three cheesemak ing replicates, with efficient control of environmental parameters (tempera ture, relative humidity, atmospheric composition) showed similar ripening c haracteristics. Deb. hansenii grew only on the cheese surface, where its ox ygen demand was satisfied, especially during the first 24 h (mean generatio n time, 5.8 h). Salting in a sterile saturated brine solution reduced its g rowth and decreased viability. Growth was slower after 48 h because of the decrease in ripening temperature (mean generation time, 94 h). The total co unt of Deb. hansenii was maximum (approximate to 3 x 10(7) yeasts/mm(2)) af ter 6 d ripening and its viable cell concentration was approximate to 2 x 1 0(6) cfu/mm(2). This difference was due to the 'non-viability' of part of t he population. The viable Deb. hansenii concentration was highly correlated (r(2) > 0.95) with the lactate concentration in the inner part and with th e surface and inner lactose concentrations, up to day 10 of ripening. This emphasized the importance of the diffusion of carbon substrate from the inn er part to the surface of the cheese during ripening. The pH of the inner p art depended significantly on the lactate and lactose concentrations, Surfa ce pH was significantly related to inner lactate concentration, temperature and relative humidity. This also demonstrated the controlling role of carb on source diffusion.