Do probiotic dairy starters adapt to vegetable milks?

In a general context of food transition, plant-based fermented products experience a considerable development. This results from evolution of consumers’ habits, demanding healthy products with a low environmental impact. This requires research and development, and thus higher scientific knowledge. Fermented soy milks constitute a favorable alternative source of live probiotics. Lactobacillus delbrueckii subsp. bulgaricus and Propionibacterium freudenreichii are extensively used in probiotic dairy products. Their adaptation to the dairy environment has been extensively studied and documented. However, little is known about their adaptation to the soy environment. We investigated suitability of soymilk as a substratefor growth and acidification by Lactobacillus delbrueckii CIRM-BIA1592 and Propionibacterium freudenreichii CIRM-BIA129. A specific focus was made on changes in term of proteome composition, cellular morphology in comparison with the cultivation in cow milk. In order to understand such adaptation, we explored their growth and survival in soy milk ultrafiltrate and compared it to cow’s milk ultrafiltrate. The two species grew in cow milk,yet not in soy milk. P. freudenreichii did grow in soy milk when co-cultured with the lactic acid bacterium L. plantarum while L. delbrueckii did not, even in co-culture with S. thermophilus. Our results revealed major differences in bacterial morphology and proteome composition. Lactobacilli upregulated stress proteins, and downregulated cell cycle and division machinery. Regarding propionibacteria, differential expression of proteins involved in amino acid metabolism, in carbohydrate metabolism, and in stress remediation was observed. These results suggest that changing the fermented substrate may significantly affect both technological and probiotic properties of conventional dairy starters. This should be considered for the development of new fermented functional foods. Screening of a large collection of lactic and propionic acid bacteria is in progress, based on their technological and probiotic properties. Bacterial stains and consortia thereof will be selected for the production of new plant-based fermented functional foods