Abstract: In order to analyze the diversity of acetic acid bacteria in naturally fermented Noni juice and enrich our knowledge of acetic acid bacteria, conventional culture method and 16S rRNA sequence homology analysis were used to identify the acetic acid bacteria from naturally fermented Noni juice and their fermentation characteristics were studied. The results showed that of the 67 strains isolated at different fermentation stages, 24 were identified as acetic acid bacteria, including Acetobacter fabarum (9 strains), Acetobacter syzygii (7 strains), Acetobacter pasteurianus (2 strains), Acetobacter tropicalis (1 strain), Acetobacter lambici (1 strain) and Gluconobacter japonicus(4 strains), and A. syzygii and A. fabarum were the dominant strains during the fermentation process. In terms of fermentation characteristics, A. tropicalis N21 showed the best performance. Its acid yield was the highest, which reached 28.92 g/L. It was able to grow well at 40 ℃ and produce 14.85 g/L of acid. At an ethanol concentration of 7%, the acid yield was decreased slightly, but it was still as high as 23.60 g/L, which shows that the temperature and ethanol tolerance of A. tropicalis N21 are superior to those of any other strains.

Key words: acetic acid bacteria, Noni (Morinda citrifolia L.), naturally fermented juice, 16S rRNA, fermentation characteristics