Do you know fermented vegetables ?
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Do you know fermented vegetables ?

Do you know fermented vegetables ?

Fermented vegetables, traditional in Asia and Eastern Europe, are booming in Western countries. They are made using a simple process consisting of incubating cut and salted raw vegetables, packed in jars in their juice or in brine, at room temperature. Fermented vegetable, apart sauerkraut, are mainly produced on a domestic and artisanal scale by spontaneous fermentation, which raises questions about their health safety.

The FLEGME citizen science project brought together more than 25 players. The scientific objectives were to explore the microbial composition of fermented vegetables. To this end, 75 samples of home-made fermented vegetables were analyzed, along with data on their manufacture, collected as part of the project. In addition, experimental productions of fermented white cabbage and carrot, prepared according to two methods of vegetable cutting (fine or coarse) and added salt content (0.8 and 1%) were carried out and analyzed.

The results showed that:

  • No pathogenic bacteria were detected either in the 75 home-made samples or in the experimental productions.
  • All the home-fermented vegetables were produced using a fairly similar process, though with differences in the way the vegetables were cut and the ingredients (vegetables, spices and herbs used). The products received ranged in age from 2 weeks to 4 years.
  • Lactic acid bacteria were in the majority in the home-made samples, as in the experimental productions. The two main species were Lactiplantibacillus plantarum and Levilactobacillus brevis. The main other bacterial group was composed of dead Enterobacteriaceae. 
  • In the experimental productions, for both vegetables and both types of cutting, the initial vegetable microbiota was rapidly replaced by Enterobacteriaceae, which in turn were gradually replaced by lactic acid bacteria. Lactic acid fermentation was more rapid in the thinly-cut vegetables than in the roughly cuts, and as a result, the number of viableEnterobacteriaceae decreased more rapidly in the finely cut vegetables. The finer the cut, the faster the diffusion of nutrients from the plant tissue into the juice.
Graphe représentant les populations bactériennes et le pH dans des carottes fermentées
© A. Thierry

Time-course of fermentation in carrot prepared with two cutting types, illustrated by the change in pH (green), and the viable counts of lactic acid bacteria (purple) and bile-tolerant Enterobacteriaceae (red). Values are means of the results observed on two to four independent jars, and the coloured areas show the confidence intervals.

These results constitute the first large-scale description of domestic production of fermented vegetables. Our work confirms the diversity and role of Enterobacteriaceae as primo-colonizers. More in-depth knowledge of these bacteria is essential to better assess the potential risks associated with them. Identifying the role of cutting in fermentation kinetics offers a simple lever to better control these spontaneous fermentations: cutting vegetables finely accelerates the decline of Enterobacteriaceae.

Collaboration

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Contacts

Anne Thierry anne.thierry@inrae.fr
Florence Valence florence.valence@inrae.fr

Financial support

This work was financially supported by the Conseil Régional de Bretagne, France, the Conseil Régional des Pays de la Loire, France, and Fonds de dotation EKIP, Paris, France, in the framework of the FLEGME inter-regional project, under the scientific coordination of INRAE and managed by the VEGEPOLYS VALLEY competitive cluster.

Modification date: 15 November 2024 | Publication date: 18 October 2024 | By: STLO