Microbiological changes in cottage cheese varieties during storage at +7°C

Studies have been made of microbiological changes in cottage cheese varieties during storage at 7°C. Commercially prepared products obtained directly from three manufacturers were at an initial pH in the range 4·6 to 5·1 and differed significantly in their content of sorbic acid/sorbate and of viable lactic streptococci. In many of the varieties that did not contain sorbic acid/sorbate multiplication occurred of Pseudomonas spp., Enterobacteriaceae and yeasts; spoilage occurred in some batches due to formation of a surface film of Pseudomonas fluorescens or of surface colonies of Sporobolomyces roseus and Trichosporon sp. at times equal to, or slightly greater than the recommended storage life. Where high numbers of viable lactic streptococci were present in varieties immediately after manufacture, no marked decrease in pH or increase in titratable acidity was observed during storage at 7°C. In varieties that contained sorbic acid at a concentration higher than approximately 500 mg kg^?1 little increase in numbers of bacteria or yeasts was observed during storage at 7°C. Decrease in quality due to separation of whey occurred in some products from each manufacturer, but no clear correlation was observed between separation of whey and pH or the number of lactic streptococci present.Bacteria of public health significance, Escherichia coli type I, Staphylococcus aureus and Vibrio spp. were not detected in these products.Fifty-nine samples produced by six manufacturers, purchased from retail outlets, were examined on the sell-by date; the results confirmed the conclusions drawn from studies during storage.