Avaliação das características físico-químicas de iogurtes naturais produzidos a partir de leite contaminado por bactérias psicrotróficas proteolíticas/ Physicochemical evaluation of plain yogurt produced by psychrotrophic and proteolytic bacteria contaminated milk

Abstract

Cooling of milk in dairy favors the multiplication of psychrotrophicbacteria that can produce thermoresistant proteolytic enzymes and degrade milk components. To verify the effects of these enzymes in dairy products, this study aimed to evaluate the physicalchemical characteristics of plain yogurt produced from milk contaminated with proteolytic psychrotrophic bacteria. For this, psychrotrophicbacteria producing proteolytic enzymes were isolated from raw milk, having been identified like Pseudomonassp., Alcaligenes sp. and Butiauxella sp. These microorganisms were inoculated in pasteurized milk and stored for 48 and 72 hours at a temperature of 7°±1°C. After the storage, the milk was heated to 90°± 5°C for 10 min and immediately cooled to 43°C. The ingredients were added and plain yogurts were produced, and then evaluated for their protein, fat and acidity contents. The plain yogurts produced, in terms of fat and protein contents, were significantly higher in yogurts produced with control milk (not inoculated). In addition, the acidity of yogurt produced with milk stored for 72 hours at 7°±1°C was significantly higher on day zero, regardless of the microorganisms intentionally added. Thus, it can be concluded that the physical-chemical characteristics of plain yoghurts produced with contaminated milks were different from those obtained from yogurts produced with non-contaminated milks, being important to reflection of the cold storage periods due to the favoring of multiplication of proteolytic psychrotrophic microorganism.