Dominant Microorganisms during the Spontaneous Fermentation of Suan Cai, a Chinese Fermented Vegetable

Microbial dynamics and biochemical processes during suan cai fermentation were investigated. The pH decreased from 7.3 to 4.0 at day 12 of suan cai fermentation, and then remained at approximately 4.1. Water-soluble carbohydrate decreased from 15.1% to 4.5% of dry matter at day 18 of fermentation. Nitrite content comprised 54.6 mg kg(-1) of fresh matter at day 6, and then decreased dramatically. Lactic acid, acetic acid and ethanol were the main volatile products identified, and concentrations were 6.8 g L-1, 0.78 g L-1 and 32.2 g L-1 at the end of fermentation, respectively. 16S rDNA clone libraries showed that bacteria during the fermentation included Acinetobacter sp., Pseudomonas fragi, Klebsiella sp., Citrobacter sp., Betaproteobacteria sp. and lactic acid bacteria, which included Leuconostoc mesenteroides, Lactobacillus curvatus, Lact. plantarum and Lact. oligofermentans. At day 6, LAB comprised 63.8% of the bacterial population. On day 30, all bacteria were LAB. Lact. curvatus dominated the fermentation. Lact oligofermentans was found to be involved in the vegetable fermentation for the first time. 26S rDNA D1/D2 clone libraries revealed that eukaryotic microorganisms included Stramenopile sp. and soil fungus at day 12. Candida sake, Cystofilobasidium infirmominiatum, Claclosporium sp. and Tilletiopsis washingtonensis were also detected until day 30 of fermentation. This is the first study to focus on eukaryotic diversity during suan cai fermentation. These results provide a comprehensive understanding of the spontaneous suan cai fermentation process and a foundation for controlling suan cai fermentation and quality.