Population Dynamics of Constitutive Microbiota in BAT Type Fermented Milk Products

Seventy samples from two batches of commercially produced fermented milk were analyzed for constitutive microbiota. Five samples were tested on the day of collection and the others analyzed after 10, 17, 24, 28, 31 and 36 days of storage at 7°C. M₁₇ agar was used to enumerate Streptococcus salivarius subsp. thermophilus . MRS (de Man, Rogosa, Sharpe) agar was used to enumerate Lactobacillus acidophilus . For the enumeration of Bifidobacterium spp. MRS agar to which antibiotic substances were added was used. In the case of Batch A, streptococci, lactobacilli and bifidobacteria were initially present at levels of 231.2 × 10⁶, 0.677× 10⁶ and 1.558 × 10⁶, respectively. The initial pH of 4.48 decreased to 4.12 after 24 days. For Batch B, streptococci, lactobacilli and bifidobacteria were initially present at levels of 858 × 10⁶, 190.7 × 10⁶ and 1.644 × 10⁶, respectively. The initial pH of 4.23 decreased to 4.07 and 3.84 after 24 and 36 days, respectively. The fall in the counts throughout refrigerated storage time showed some irregularities which, in our opinion, indicate a lack of control over the ecological aspects which affect the interrelation between the microorganisms involved. The statistical significance of the differences between the different trials was established throughout the time.