Anne-Cecile Leforestier

1. Spontaneous vegetable fermentation is driven by the indigenous microbiota associated with the raw ingredients. The process often involves an initial heterofermentative phase followed by a predominantly homofermentative phase, both ensured by lactic acid bacteria (LAB). While microbial dynamics during fermentation are well characterized, phage communities remain poorly understood, despite evidence linking phage activity to LAB succession. We monitored viral and bacterial succession during sauerkraut and carrot fermentations using a metagenomics approach to characterize community dynamics. To further assess the impact of phage PLE001 on bacterial community dynamics, we developed a simplified carrot fermentation model comprising representative strains of Rahnella aquatilis, Leuconostoc mesenteroides and Lactiplantibacillus plantarum. Two consortia were assembled: one containing the PLE001-susceptible strain L. mesenteroides CIM3004, and the other containing also its phage-resistant derivative, CIM3004 BIM. We observed major shifts in the viral community during the first week of fermentation, coinciding with changes in bacterial structure during hetero- and homofermentative phases transition. In the simplified model, phage PLE001 reduced the population of the host during the heterofermentative phase but did not affect overall fermentation dynamics nor metabolite production. These results suggest that bacteriophages contribute to bacterial succession during fermentation, while communities remain resilient to phage infection, preserving fermentation stability.

The rising demand for sustainable food sources increased the development of plant-based ingredients. Pea protein isolate (PPI) is valued for its nutritional and functional properties, yet its application is limited by the presence of 'green' and 'beany' off-flavors. This study evaluated a bioconversion strategy using a high microbial concentration and a short-duration treatment to achieve flavor-modulation of PPI, avoiding the addition of masking agents such as flavorings and sugars. Ten microbial strains (six bacteria and four yeasts) were applied to 12% (w/w) PPI solutions. Samples were analyzed for growth kinetics, volatile composition, and sensory profile. While microbial counts remained stable, metabolic activity had a significant impact on the volatile profile. Remarkably, within just six hours, key off-flavor aldehydes (e.g., hexanal, nonanal) were depleted across most strains, drastically reducing their Odor Activity Values. Distinct aroma profiles emerged: Kluyveromyces lactis and Lacticaseibacillus paracasei not only eliminated off-flavors but generated fruity esters and nutty-like notes. Conversely, lactic acid bacteria like Streptococcus thermophilus produced diacetyl and 2,3-pentanedione, enhancing creamy/lactic notes, while Geotrichum candidum generated samples presenting a neutral sensorial profile. A correlation between metabolomic and sensory data confirmed that short-time bioconversion is a potent, minimal-processing tool to tailor the aroma of plant protein isolates.