MICROBIOLOGICAL AND PHYSICAL-CHEMICAL QUALITY OF THE REFRIGERATED RAW MILK ADDED WITH CARBON DIOXIDE

The objective of this research was to evaluate the effect of carbon dioxide (CO2) addition and storage temperature as well as interactions of these factors on microbial growth, proteolysis and lipolysis of refrigerated raw milk. Raw milk, with and without CO2 addition was stored in glass bottles at 4 and 7 degrees C. Samples were daily analyzed to standard plate count and psychrotrophic count and every otherday to CO2 concentration, proteolysis and lipolysis, until standard plate count reached 7,5x10(5) CFU/mL. The standard plate count increased during refrigerated storage time for all treatments. However, to samples stored at 4 degrees C the time required to reach the limit count was 14 days to raw milk with CO2 addition and 8 days to raw milk without CO 2 addition. For samples at 7 degrees C this time was 8 and 5 days, respectively. Independent of the storage temperature, CO2 addition extended psychrotrophic lag phase and generation time and decreased growth rate in raw milk, with higher efficiency at 4 degrees C. Milk with CO2 addition presented lower proteolysis and lipolysis, possibly related to lower psychrotrophic count and reduction of proteinases and lipases production in these samples. CO2 addition enabled the maintenance of raw milk quality for a longer time and can be used to prevent quality problems in processed products.