Factors affecting the multiplication and survival of coagulase positive staphylococci in Cheddar cheese

Abstract

The presence of a thermolabile inhibitor of coagulase-positive staphylococci in milk was confirmed. Starter streptococci significantly suppressed the multiplication of staphylococci in milk not only by their acid production but also by some other competitive effect.Cheesemaking trials showed that staphylococci multiplied considerably more rapidly in 'slow' or 'sweet' cheese, where the starter was inhibited by phage, than in normal cheese. Little decrease in numbers occurred in 'sweet' cheese even after 18 months, in contrast to the rapid decline in the normal cheese.Staphylococci subjected in the laboratory to sublethal heat treatments had a prolonged lag phase on all media and their % recovery on selective media was significantly lower than on optimal non-selective media. It is suggested that the low survival rate of the staphylococci in cheese made from milks heated at sublethal temperatures is due to the lag in recovery of heat-shocked cells and their inability to multiply in the unfavourable cheese curd.

Effects of heat, processing time and pH on the microflora, aflatoxin content and storability of “wara”, a soft, white cheese

“…Our present findings are thus in agreement with other reports confirming that reduced pH value could to some extent be inhibitory to the growth of some bacteria [2,25]. Furthermore, in line with our findings, in a study of the microflora at various stages of processing fluid milk, a reduction from lo' to 5 .…”

Relationship of the Microflora to the Flavour of Cheddar Cheese

“…I n the cheese industry, single strain or multiple strain starters are used, consisting of lactic acid streptococci and leuconostocs. Raw milk, which contains a complex bacterial flora, is a t present heat treated sufficiently to eliminate coagulase positive staphylococci (Reiter et al, 1964;Sharpe et al, 1965) and the bacteria in the cheese curd arise from contamination in the factory. Once some form of continuous cheesemaking process becomes adopted, fortuitous contamination is likely to be excluded and if the bacteriological quality of the cheese milk further improves, we may have to consider a suitable method of inoculating the milk with a reference flora either before or after heat treatment to produce a mature cheese in a reasonable t i e .…”

A centenary of academic and less learned Food Microbiology Pitfalls of the past and promises for the future

“…This risk assessment is based on experimental data adopted from Hendricks et al, 1959;Allen and Stovall, 1960;Reiter et al, 1964;Zehren and Zehren, 1968;Scheusner et al, 1973;Tatini, 1973;Stadhouders et al, 1978;Van Schouwenburg-Van Foeken et al, 1979;Liick and Dunkeld, 1982;Ratkowsky et al, 1982;Bennett and Amos, 1983;Melconian et al, 1983;Holmberg and Blake, 1984;Waes and Bossuyt, 1984. where an unbiased verdict has to be formed on to the acceptability of a variety of food-processing and preservation techniques. It lends itself, moreover, admirably to analysing industrial cost-benefit situations wherein often far-reaching decisions have to be taken .…”