Communautés microbiennes de légumes fermentés domestiques et artisanaux

International audienceFermentation of vegetables has recently received a renewed interest in the USA and in Western Europe, where they are little consumed, in contrast with central Europe and Asia. FLEGME is a citizen science project focused on fermented vegetables, which gathers various actors including citizens, SMEs, agricultural schools, culinary journalists, and researchers. One of its goal is to characterize the microbial communities and the safety of home-made fermented vegetables. A set of 75 fermented vegetables was collected from citizens that manufacture such products for their personal consumption. Several microbial groups were analysed by culture-dependent methods, including lactic acid bacteria (LAB), yeasts, and some pathogenic bacteria. pH was also measured. 1 to 3 isolates were randomly picked up from LAB and yeast plates and identified by 16S and D1/D2 sequencing. Samples were also analysed by metabarcoding analysis. The received included 23 types of vegetables, mainly cabbage (27%), followed by carrots (19%) and beets (12%). Their age ranged from 2 weeks to 4 years. Their median pH was 3.6, only 2 samples had a pH over 4.5. LAB represented the dominant population. Their median concentration was 7.5x104 CFU/g, but varied from non-detectable values to 6x108 CFU/g. No significant relationship was found between LAB counts and the type of vegetable. However, LAB counts significant depended on the age of samples, with high LAB counts most frequently observed in the youngest samples (< 100 days). Yeasts were detected in nearly half the samples, with counts ranging from 102 to 9x107 CFU/g. Enterococci were detected in only 5 samples at counts < 105 CFU/g. No pathogenic bacteria were detected. 90 LAB clones and 47 yeast clones were isolated, belonging to 31 species, the most common being Levilactobacillus brevis and Lactiplantibacillus plantarum/paraplantarum (21 and 20 % of total bacterial isolates, respectively) and Saccharomyces cerevisiae, Debaryomyces hansenii, and Wickerhamomyces anomalus for yeasts. Metagenomic results showed that Lactobacillacae was the most represented family, with Lactiplantibacillus as most frequent genus encountered), followed by Streptococcaceae, Leuconostocaceae and Staphylococcaceae, with Lactococcus, Weissella, and Staphylococcus, respectively, as most frequent genera