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

Abstract

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°C. Samples were daily analyzed to standard plate count and psychrotrophic count and every other day to CO₂ concentration, proteolysis and lipolysis, until standard plate count reached 7,5x10⁵ CFU/mL. The standard plate count increased during refrigerated storage time for all treatments. However, to samples stored at 4°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 CO₂ addition. For samples at 7°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°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.