Influence from raw milk flora on cheese ripening studied by different treatments of milk to model cheese

To study the influence from the raw milk microbial flora on the biochemistr y of cheese during ripening, cheese was made in an unreplicated 2(3) full f actorial design in two blocks of four cheese vats. Semi-hard round-eyed mod el cheese with 45% fat in dry matter and a moisture content of 55% was made from raw, pasteurized and microfiltered skim milk in combinations with raw or pasteurized cream. Indices of proteolysis, amino acid composition, carb oxylic acids, and volatile flavour compounds in cheese were analysed on fou r-occasions during 120 days of ripening. Breakdown of casein progressed sim ilarly in all cheeses and the influence of with treatments was first seen i n the varying composition of the amino acids. Principal component analysis (PCA) of the amino acid composition data showed a clear separation of the c heeses during ripening. The PCA separated the cheeses firstly by age and th en by milk treatment. The cheeses made from unpasteurised and non-microfilt ered milk (raw skim milk) separated out in one direction, and to some exten t in the same direction those with only the cream untreated. In cheeses pro duced from raw skim milk,to citrulline was present and arginine increased s lightly during ripening contrary to cheeses produced from treated skim milk . Typically for the raw milk cheeses, the results indicated: production of gamma -amino butyric acid (GABA) from glutamic acid, histamine from histidi ne, tyramine from tyrosine and utilization of serine. An increase in the py ruvate content could be seen in all cheeses at the end of the ripening peri od. Formic acid and 2-butanol were only found in cheeses made with raw skim milk of raw cream, while ethanol was produced in all cheeses, but to a gre ater extent in the cheese from raw milk. Non-starter lactic acid bacteria ( NSLAB) were found at higher numbers in cheese from raw milk or cream. (C) 2 000 Academic Press.