236. The bacterial flora of New Zealand Cheddar cheese

Of the lactic acid bacteria isolated, 720 strains from thirty-six typical Cheddar cheeses have been classified. The dominant organism in New Zealand cheese has been shown to be Sbm. plantarum. Sbm. casei occurs much less frequently, while betabacteria and betacocci are found in still smaller numbers. Betabacteria tend to replace Sbm. plantarum in the final stage of cheeseripening. The flora of good quality cheese has been found to consist mainly of one or two varieties of Sbm. plantarum, often associated with Sbm. casei or a small proportion of betabacteria. In poor-quality cheese a larger number of types of lactic acid bacteria frequently occur. A simple routine method is described for distinguishing the different groups present in cheese.

The effects which different strains of lactobacilli and betacocci produce in cheese have been correlated with their biochemical characteristics. Sbm. casei in general appears to be beneficial to cheese quality. The strains of Sbm. plantarum isolated have been grouped in four varieties, mainly on the basis of sugar reactions; one variety has been shown to be beneficial to cheese quality, another variety has very little apparent effect, while the remaining two varieties produce serious defects—bad flavours, discoloration and, occasionally, open texture. The same defects are produced by most strains of betabacteria and betacocci when present in large numbers.

The biochemical characteristics of the lactobacilli studied have shown a more regular gradation from Sbm. casei through Sbm. plantarum to Bbm. breve (the only species of Betabacterium isolated) than is indicated from the generally accepted systems of classification.