61. Discoloration in New Zealand Cheddar Cheese. Muddy, Bleached and Pink Defects. II. Biochemical Investigations

151. The reactions and properties of annatto as a cheese colour, with particular reference to the chemistry of cheese discoloration

The properties of commercial annatto solutions have been examined from the point of view of the cheese-making process.

(1) The effect of initial colour strength, pH of the medium and distribution during manufacture are recorded.

(2) Methods are described for the extraction of the annatto colour from milk products.

(3) The effects of old annatto solutions, metallic impurities (copper and iron) and sulphydryl are shown.

(4) It is suggested that the mechanism underlying the development of “bleached” and “pink” discoloration in cheese is an oxidation process, and the effect of oxidation on annatto solutions has been studied in some detail.

(5) Suggested standards for annatto extracts for use as cheese colours are appended.

422. Cheese discoloration: oxidation of bixin in annatto-coloured cheeses promoted by sulphydryl compounds

Some years ago discoloration was reported in mature New Zealand export cheeses. The defect occurred typically as bleached or pink areas surrounding cracks, though a less frequent ‘muddy’ discoloration was also noted. Discoloration was, on the whole, restricted to cheeses made in warm weather. Preliminary observations showed that the defect had certain characteristic features, viz.

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 beSbm. plantarum. Sbm. caseioccurs much less frequently, while betabacteria and betacocci are found in still smaller numbers. Betabacteria tend to replaceSbm. plantarumin the final stage of cheeseripening. The flora of good quality cheese has been found to consist mainly of one or two varieties ofSbm. 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. caseiin general appears to be beneficial to cheese quality. The strains ofSbm. plantarumisolated 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 fromSbm. caseithroughSbm. plantarumtoBbm. breve(the only species ofBetabacteriumisolated) than is indicated from the generally accepted systems of classification.