Influence from Raw Milk Flora on Cheese Ripening Studied by Different Treatments of Milk to Model Cheese

Abstract

To study the influence from the raw milk microbial flora on the biochemistry of cheese during ripening, cheese was made in an unreplicated 23full factorial design in two blocks of four cheese vats. Semi-hard round-eyed model 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, carboxylic acids, and volatile flavour compounds in cheese were analysed on four occasions during 120 days of ripening. Breakdown of casein progressed similarly in all cheeses and the influence of milk treatments was first seen in the varying composition of the amino acids. Principal component analysis (PCA) of the amino acid composition data showed a clear separation of the cheeses during ripening. The PCA separated the cheeses firstly by age and then by milk treatment. The cheeses made from unpasteurised and non-microfiltered milk (raw skim milk) separated out in one direction, and to some extent in the same direction those with only the cream untreated. In cheeses produced from raw skim milk, no citrulline was present and arginine increased slightly during ripening contrary to cheeses produced from treated skim milk. Typically for the raw milk cheeses, the results indicated; production of γ -amino butyric acid (GABA) from glutamic acid, histamine from histidine, tyramine from tyrosine and utilization of serine. An increase in the pyruvate content could be seen in all cheeses at the end of the ripening period. Formic acid and 2-butanol were only found in cheeses made with raw skim milk or raw cream, while ethanol was produced in all cheeses, but to a greater 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.