Mustard green (Brassica juncea L var. rugosa) is popularly consumed in Thailand as salted or sour pickled
vegetable. Naturally occurred lactic acid bacteria (LAB) from the raw ingredients play an important role in fermentation
of sour pickled mustard green. Unsuccessful sour taste development is one of the major problems in the sour pickle
industry. Therefore this study aims to study the LAB diversity and their changes during fermentation of the sour pickled
mustard green, both in natural fermentation and in starter culture-added fermentation. This knowledge will help
understanding and developing starter culture for successful fermentation. The experiment was conducted at the pickled
mustard green factory with industrial-scale fermentation facility. A control batch without starter culture and two
batches of starter culture-added at two different concentrations were fermented at room temperature for 12 days. LAB
were isolated on de Man, Rogosa and Sharpe (MRS) agar supplemented with 0.5% CaCO3 at day 0, 3, 7, and 12 of
fermentation. Ten bacterial colonies were randomly selected from each time point and genomic fingerprint of each
isolate was generated using repetitive element-based PCR (rep-PCR) technique. The control batch without starter
culture showed sign of spoilage indicated by increase in pH from 3.33 to 4.44 at day 7 while in the starter culture-added
batches the pH remained low throughout the fermentation period. Analysis of the bacterial diversity revealed succession
of the LAB species from Weissella spp. to Lactobacillus plantarum in naturally fermented batch and from Weissella
spp. to Lactobacillus fermentum in starter culture-added batches.