Abstract: Ten strains of lactic acid bacteria from different sources including fermented fruit were screened for tolerance to stress conditions. Lactobacillus plantarum ZG2 and Lactobacillus casei GG8 were selected as the best for the fermentation of pear juice. We compared the fermentation performance of the two strains by measuring the viable count, pH value, organic acids and volatile components of pear juice during the fermentation process. The results showed that the viable count of ZG2 decreased rapidly during the early part of the fermentation process, lasting for a short time of period. The pH value at the end of fermentation for GG8 was lower than that for ZG2. The organic acid compositions of the two fermented juices were similar although ZG2 exerted stronger lactic acid-producing ability while GG8 produced larger amounts of citric acid and total acids. The primary flavor compounds of pear juice changed little before and after fermentation, 2-methoxy-3-methylpyrazine, linalool and terpineol. Both strains produced the most abundant volatile compounds during the middle stage of fermentation, and GG8 also produced abundant volatile compounds during the late stage. Compared with L. plantarum ZG2, L. casei GG8 has greater potential for research and application.

Key words: lactic acid bacteria, pear juice fermentation, tolerance, screening, fermentation characteristics