Determination of Probiotic Viability in Yoghurts Produced with Acid Adapted Lactobacillus acidophilus ATCC 4356 and Bifidobacterium bifidum ATCC 11863 During Refrigerated Storage

Microorganisms have various stress response systems to maintain their viability when exposed to different stress conditions. In this study, Lactobacillus acidophilus ATCC 4356 and Bifidobacterium bifidum ATCC 11863 strains, used in probiotic yoghurt production, were subjected to acid (lactic and hydrochloric acid) stress to induce acid tolerance response (ATR). Yoghurts produced with both acid-adapted and non-adapted strains were stored at +4°C for 21 days. During the storage period, the pH and titratable acidity values of the yoghurts were measured, and the viability levels of the probiotic strains in the yoghurts were determined. In all yoghurt groups, a decrease in pH values and an increase in titratable acidity were observed during storage. The highest viability levels of the probiotic strains were detected on the first day of storage. Lactic acid-adapted Lb. acidophilus ATCC 4356 and B. bifidum ATCC 11863 in yoghurt showed growth at a level of 8.08 ± 0.12 and 8.08 ± 0.09 log10 Cfu/g at the first day of storage, respectively. Additionally, hydrochloric acid-adapted Lb. acidophilus ATCC 4356 and B. bifidum ATCC 11863 in yoghurt exhibited growth at levels of 7.90 ± 0.08 and 5.99 ± 0.03 log10 Cfu/g, respectively. The viability of acid-adapted Lb. acidophilus ATCC 4356 and B. bifidum ATCC 11863 showed a decrease similar way to that of the control group (non-acid adapted) during the storage period.