Evaluation the effect of Lactobacillus acidophilus probiotic culture over Staphylococcus aureus during the production and storage of acidophilus yoghurt

The survival of Staphylococcus aureus in the acidophilus yoghurt (AY) was evaluated during the production and coldstorage. 21 acidophilus yoghurt samples were prepared with traditional yoghurt culture (Streptococcus thermophiles &Lactobacillus bulgaricus) with Lactobacillus acidophilus and inoculated with 106 cfu/ml S. aureus and stored for 21 daysat 4oC. Samples were taken at zero time (fresh samples), 3, 5, 7, 10, 14 and 21 days for titratable acidity, culture starters’counts and S. aureus count. The results revealed that the titratable acidity% of AY was increased and reached 0.72, 0.78,0.83, 0.87, 0.89, 1.02 and 1.45% at zero time, 3, 5, 7, 10, 14, and 21 days of storage, respectively, while the population of S. aureus reached 6.10 and 3.70 log10cfu/g at zero time and 3rd day of storage, respectively and became non-detectable level in 5th days of storage. The count of all starter cultures (S. thermophiles+ L. bulgaricus+ L. acidophilus) in acidophilus yoghurt increased during the fermentation and cold storage, S. thermophiles became 7.15, 7.35, 8.20, 8.15, 7.45, 7.45 and 6.65 log10cfu/g while L. bulgaricus 7.25, 7.55, 8.25, 8.73, 7.76, 7.47 and 6.54 log10cfu/g and L. acidophilus became 7.38, 7.70, 8.25, 8.20, 7.50, 7,46 and 6.66 log10cfu/g at zero time, 3, 5, 7, 10, 14, and 21 days of storage, respectively. It concluded that S. aureus count decreased gradually during the production and cold storage and became non-detectable level on the 5th days of cold storage. The survival of all starter cultures in yoghurt sample remained stable with values > 6 log10 cfu/g throughout the storage period at 4±1°C.