Microbial Diversity And Flavor Formation In Onion Fermentation

The traditional (without salt) fermentation of onion juice was studied through amultiphasic approach, including microbiological and metabolite target analyses. Aculture-independent (PCR-denaturing gradient gel electrophoresis, PCR-DGGE) approachrevealed onion juice fermentation process results from the growth of a complex microbialpopulation， including the lactic acid bacteria (LAB, Lactobacillus zymae, Lactobacillusmalefermentans, Lactobacillus plantarum), acetic acid bacteria (AAB, Acetobacterpasteurianus, Acetobacter orientalis), and yeasts (Candida humilis, Kazachstania exiqua,Saccharomyces bulderi). Citrobacter freundii was firstly detected in the vegetablefermentation. In addition, Quantitative real-time polymerase chain reaction (qRT-PCR)revealed that the content of L. plantarum was increasing during almost the whole spontaneousfermentation. And the relative high expression time of ldhL was at the first half of thefermentation. Taste and flavour compounds changes between the raw and the fermented onionjuice were also detected by HPLC and HS-SPME-GC-MS. The organic acid analysis showedthat the lactic acid and acetic acid were the new nutrition of the fermented product. Thissuggested that onion juice fermentation was spontaneous lactic acid fermentation. Afterfermentation, the type of amino acids had no significant changes, but the total concentrationof amino acids significantly decreased after the fermentation with salt. Fermentation made thevolatile compounds richer in the onion juice. More esters, alcohols, aldehydes, and ketoneswere identified in the end products. And the formation of organic acid, amino acid, andvolatile compounds were all influenced by salt. This work may found a basis for the furthermodification of the fermentation process.