Influence of the combination of probiotic cultures during fermentation and storage of fermented milk

The objective of this study was to evaluate the influence of different combinations of cultures, Lactobacillus acidophilus — La and Bifidobacterium animalis subsp. lactis — Bb as pure cultures or in co-culture with Streptococcus thermophilus — St, on fermented milk during fermentation, including changes to the acidification profile, organic acid production and lactose consumption and during 28-day storage at 4°C, in terms of bacteria viability, syneresis, sensory properties, organic acid content and viability under simulated in vitro gastrointestinal conditions. La culture was showed the lowest acidification rate (Vmax) values, whereas the pure St culture showed the highest Vmax values. During fermentation, Bb produced the largest amount of acetic acid, and only La was able to metabolize citric acid. Syneresis decreased during storage for all treatments. Counts of S. thermophilus and B. animalis subsp. lactis remained stable during the storage period in all treatments, while the counts of L. acidophilus decreased over time only in the case of the La treatment. The simulation of probiotic resistance to gastrointestinal conditions indicated that bifidobacteria possess a greater tolerance to acid and bile than the lactobacilli strain. The La treatment resulted in lower scores for all attributes in both periods of sensory analysis. When lactic acid was present in smaller quantities and citric acid was present in larger amounts, the scores regarding flavor and overall acceptability attributes were higher. Depending on the combination of microorganisms used in fermented milk manufacturing, it had positive or negative impacts on the product's characteristics. •Culture composition affected the organic acid contents and acidification parameters.•The syneresis reduced during storage and was affected by culture composition.•BB-12 strain was more resistant to simulated GI conditions than La-5 strain.•The scores obtained in sensory analysis were affected by culture composition.•Sensory attributes scores were correlated to the amounts of lactic and citric acids.