Synergistic fermentation of reconstituted milk fortified with kiwi juice by Saccharomyces boulardii and lactobacilli strains
摘要
The interaction between Saccharomyces boulardii, a non-lactose-fermenting yeast, and lactic acid bacteria was examined during the fermentation of reconstituted milk fortified with kiwi juice (4% v/v), focusing specifically on microbial growth, pH development, sugar utilization, and ethanol production. The co-cultivation of S. boulardii with lactobacilli resulted in a more pronounced pH reduction compared to fermentation with S. boulardii alone. Specifically, co-inoculation with Lacticaseibacillus casei 20,975 led to a minimum pH of 3.51 (P < 0.05) within 6 h, accompanied by a maximum viable cell count of 8.00 × 1010 CFU.mL− 1. When Limosilactobacillus fermentum F16 and Lactiplantibacillus plantarum JXJ (6–12) were present, the pH decreased to 4.23 and 4.09, respectively. In monoculture, S. boulardii directed sugar utilization primarily toward ethanol production (5.68 mg/100 g) rather than acidification (pH ≥ 4.83). Ethanol levels increased significantly, reaching 51.86 mg/100 g, when Lb. plantarum RS (35 − 11) was co-cultured with S. boulardii during fermentation at 37 °C for 4 h. In contrast, ethanol production in reconstituted milk without kiwi juice reached only 22.84 mg/100 g after 6 h at 37 °C. Enhanced growth of Lb. casei 20,975, Lb. plantarum JXJ (6–12), and Lb. fermentum F9 was associated with a reduced ethanol production (≤ 11.65 mg/100 g). Ethanol accumulation inhibited the growth of lactobacilli, resulting in a final viable cell count ranging from 2.60 × 106 to 5.80 × 108 CFU.mL− 1 at the end of fermentation. These findings highlight the adverse effects of lactobacilli-derived metabolites such as lactic acid, acetic acid, and bacteriocins, which accumulate in the fermentation environment, reduce pH, and disrupt membrane integrity in both bacterial and yeast cells. Co-cultivation with S. boulardii, capable of utilizing these metabolites as nutrients, may attenuate inhibitory effects, particularly when fermentation time is appropriately managed.