ABSTRACT
Milk is an ideal medium for microbial growth because of its high water content, neutral pH and biochemical composition. Therefore, raw milk may contain various kinds of microorganisms with variable characteristics in respect to classifi cation, morphology and physiology. Very important for the quality of raw milk and dairy products are bacteria that predominate among all kinds of milk microorganisms. Bacteria in raw milk can be spoilage or pathogenic with mesophilic, psychrophilic or thermophilic behavior. In brief, bacterial growth is divided into four phases: i.e., lag, exponential or log, stationary and dying-off phases (Walstra et al. 2006). Multiplication of bacteria shows a geometric progression and the bacterial growth during the log phase is described by the generation time (g) that is the time needed for a full cell division. Generation time in raw milk depends mainly on species or strains of bacteria as well as temperature, pH, level of oxygen, inhibitors and nutrients. Thus, the profi le of initial microfl ora and the handling of raw milk regarding hygienic and temperature conditions are the determinative factors for raw milk quality before processing. Raw milk microfl ora is of critical importance for consumers’ safety and quality and shelf-life of dairy products. Raw milk microfl ora could be grouped as indigenous or contaminants and also as spoilage or pathogenic microorganisms.
