PSYCHOTROPYTICS IN RAW MILK: EFFECT ON MEAN COMPOSITION OF PROVOLONE TYPE CHEESE

High contamination by psychrotrophic populations (5 to 6 log UFC/mL) in raw milk influences the quality of milk and derivatives such as cheeses, as they produce proteolytic and lipolytic thermoresistant enzymes. These enzymes can alter the shelf life of the product, causing technological problems like loss of yield, bitter taste and rancidity that compromise the quality of milk and especially of the derivatives. The objective of this study was to evaluate the influence of the population of the raw milk psychrotrophic microorganisms on the centesimal composition of the provolone cheese during 60 days of maturation. Two types of raw material were selected for the production of 3 lots of provolone type cheese (A and B): A treatment was produced from raw milk refrigerated with 3±1 log UFC/mL of psychrotrophs, and treatment B, with counts of 7±1 log UFC/mL. The milk for the production of the cheeses was pasteurized (72±2ºC/15 to 20 seconds), cooled to 32±3ºC and sent to the cheeses. The cheese samples were evaluated at zero times, 30 and 60 days of production by fat analysis (%) by the Gerber method and humidity (%) by thermogravimetric equipment. The proteolytic changes during cheese maturation (zero, 30 and 60 days) were evaluated by the Kjeldahl method, evaluating the total nitrogen (NT), non - casean nitrogen (NNC) and non - protein nitrogen (NNP) levels. The primary proteolysis index (PPI) was determined from the NNC / NT ratio and the secondary proteolysis index (IPS) by NNP/NT. To evaluate the influence of milk quality on cheeses composition and proteolysis index, multiple regression was used, with 2x3 experimental design as a function of humidity, fat percentage, NT, IPP and IPS. The independent factors were the microbiological load and the maturation time. The microbiological quality of the milk influenced only the amount of fat obtained in the cheeses, in which a linear and negative relation was observed (p<0.01). The maturation alone influenced in the humidity (p<0.01), fat percentage, total nitrogen (p<0.01) and secondary proteolysis indexes (p<0.01). It was concluded that cheeses with milk with higher microbiological load were associated with lower fat percentages and maturation contributed with increased levels of fat, total nitrogen and secondary proteolysis.