Probiotic viability, pH and lactic acid concentration of opened commercial probiotic dairy drinks stored at different temperatures and durations

Abstract

Background The commercial cultured milk drinks contain either single or mixed probiotic species and supply in different serving sizes. It is known that different combinations of probiotics might provide the various products’ quality in terms of nutritional value during their manufacturing process. However, a lack of information about probiotic viability and physicochemical properties of the opened fermented products for continuous fermentation leads to the driving force in conducting this study. Therefore, four locally available cultured milk drinks (branded Y, F, N and V) with 20 bottles each were aseptically transferred into their respective sterile containers and stored at 4 °C, 25 °C and − 20 °C for 1–13 days. Then, the viable cells were quantified using the drop plate method on de Man, Rogosa and Sharpe (MRS) agar. The pH change was investigated using the calibrated pH meter, and the Enzytec D-/L-Lactic acid kit determined the content of D-lactic acid via spectrophotometer. Eventually, the data were analysed using the statistical tool. Results The viability of probiotics in brands Y and V was significantly increased even when stored at − 20 °C and 4 °C with at least 1 log CFU/mL increment. The proliferation of probiotics was moderately influenced by the pH of the opened cultured milk. High content of D-lactate was found in Y- and F-branded products after 13 days of storage. The Y-branded cultured milk drink had the highest content of D-lactate with 0.52 g/L and 0.40 g/L when stored for 13 days at room temperature and 4 °C, respectively. Conclusions This study sheds light on the necessity to elucidate the properties of opened probiotic beverages over time, especially when bottled in large quantities. This allows some improvement steps.