Growth and survival characteristics of Paucilactobacillus wasatchensis WDCO4

Understanding characteristics that permit survival and growth of Paucilactobacillus wasatchensis as part of the nonstarter microbiota of cheese is important for minimizing unwanted gas formation in cheese that can cause downgrading because of slits and cracks. The ability of Plb. wasatchensis WDC04 to survive pasteurization was studied by inoculating raw milk with 10⁸ cfu/mL and measuring survival after processing through a high-temperature, short-time pasteurizer. Extent and rate of growth of Plb. wasatchensis WDC04 as a function of pH, salt concentration, and presence of various organic acids were studied using 48-well microplates in an automated spectrophotometer measuring optical density at 600 nm. Better growth in the 1-mL wells was obtained when a micro-anaerobic environment (similar to that which occurs in cheese) was created by enzymically removing the oxygen. Faster growth occurred around neutral pH (pH 6 to 8) than at pH 5 (cheese pH), whereas only marginal growth occurred at pH 4. Adding sodium chloride retarded growth of Plb. wasatchensis WDC04, but slow growth occurred even at salt concentrations up to 6%. At salt-in-moisture (S/M) concentrations found in cheese, the rate of growth at 3.5% S/M >4.5% S/M >5.5% S/M. Thus, low salt level in cheese is a risk factor for Plb. wasatchensis growth during cheese storage and unwanted slits and cracks. Some of the organic acids tested (propionic, formic, and citric) tended to suppress growth of Plb. wasatchensis WDC04 more than would be expected from their effect on pH. No survival of Plb. wasatchensis WDC04 after pasteurization was observed with the reduction in numbers being 8 logs or more. Even subpasteurization heating at 69°C for 15 s was sufficient to inactivate Plb. wasatchensis WDC04, so its presence as part of the nonstarter microbiota of cheese should be considered as a postpasteurization environmental contamination.