Purpose: This work was conducted to investigate the effect of initial contamination level of Salmonella Enteritidis on the behaviour of yoghurt starter cultures (Streptococcus thermophilus and Lactobacillus bulgaricus) during milk fermentation.
Methods: The counts of yoghurt cultures were determined every 30 min by plate count method. To find the significance among the initial contamination levels of Salmonella Enteritidis on the behaviour of yoghurt starter cultures, the one-way ANOVA was utilized using the SPSS software (version 11.5). The experiments were repeated three times.
Results: The counts of yoghurt cultures contaminated by Salmonella (approximate level of 3, 5, 7 log CFU/mL) were found to be 7.07 ± 0.07, 7.17 ± 0.15 and 7.00 ± 0.12 log CFU/g, respectively, for Streptococcus thermophilus and 6.74±0.31, 6.88 ± 0.22 and 6.58 ± 0.05 log CFU/g, respectively, for Lactobacillus bulgaricus at the beginning of the fermentation. For the same initial Salmonella contamination levels, the counts were found to be 8.25 ± 0.06, 8.30 ± 0.14 and 8.18 ± 0.20 log CFU/g, respectively, for Streptococcus thermophilus and 8.81 ± 0.11, 8.86 ± 0.06 and 8.89 ± 0.14, respectively, for Lactobacillus bulgaricus at the end of the fermentation. On one hand, the initial contamination level of Salmonella did not significantly influence the behaviour of yoghurt starter cultures during fermentation (P>0.05). On the other hand, Salmonella survived in milk throughout the fermentation process for all contamination levels.
Significance: Even though the behaviour of yoghurt starter cultures are not affected by high contamination level of Salmonella, the pathogen may still survive during fermentation, even at a low contamination levels, leading to significant risk to consumers.