Effect of processing conditions on the microbiological quality of white pickled cheese

Effects of starter culture, nisin, H₂O₂ and potassium sorbate on Listeria monocytogenes, Staphylococcus aureus and Salmonella typhimurium in white pickled cheese made from pasteurized milk with 4% salt and preserved in 4% brine solution at 4°C for 60 days was studied. The starter culture inhibited all three pathogens while antimicrobials did not. Beyond day 50 in curd and day 30 in brine solution, L. monocytogenes was not detected by direct plating. S. aureus was not detected after day 30 in curd and day 20 in brine solution. S. typhimurium was not detected after day 30 in cheese curd, and was not detected in brine solution at any time. The pH of brine solution of starter treatment dropped below 4.7 in all experiments, while antimicrobial treatments had always pH above 5.5.

The chemical composition of white pickled cheese made from pasteurized milk with 8% salt and preserved in the whey at 4°C for 60 days was determined, and the cheese was challenged with L. monocytogenes. While fat, protein, total solids and ash contents decreased in curd during ripening, the acidity and salt did not change. In cheese whey, fat, protein, acidity and salt showed a slight increase while total solids and ash contents were unchanged. High salt did not affect L. monocytogenes and suppressed the activity of lactic acid bacteria such that they were not able to produce acid and inhibit L. monocytogenes. During ripening, the pH never decreased below 6.0.

A single strain of Lactococcus lactis ssp. cremoris was isolated from a commercial cheese culture and chemical mutation was attempted to develop salt-resistant mutants for use in high salt white pickled cheese. No salt-resistant mutant was isolated.