Abstract: The fermentation of Fuji apple juice by lactic acid bacteria was optimized and changes in organic acids during fermentation were analyzed. Lactobacillus paracasei 20241, Bifidobacterium animalis 6165, Streptococcus thermophilus 6063 and Lactobacillus acidophilus 6005 were used as mixed cultures in the fermentation of apple juice. The optimization of culture composition, inoculum size and fermentation time was performed using one-factor-at-a-time method and response surface methodology. Viable cell count and sensory score were used as response variables. The results showed that the optimal fermentation conditions were as follows: ratio of four probiotic strains, 1:1:1:1; inoculum size, 2%; fermentation time, 24 h; and temperature, 37 ℃. Under these conditions, viable cell count was 1.985 × 108 CFU/mL and sensory score was 80.23 points. Malic acid and succinic acid contents decreased significantly after fermentation (P < 0.05), while lactic acid, quinic acid, citric acid, tartaric acid, pyruvic acid and shikimic acid contents significantly increased (P < 0.05) as demonstrated by HPLC analysis.

Key words: lactic acid bacteria, apple juice, fermentation, process optimization, organic acids