MICROBES ON THE MENU: INVESTIGATING FOOD AS A VEHICLE FOR MICROORGANISMS FOR THE HUMAN INTESTINAL ECOSYSTEM

The Microbial Deprivation Hypothesis states that exposure to harmless microorganisms at an early age is essential for the correct development of the immune system, decreasing the risk of incidence of autoimmune diseases and allergic disorders later in life. The methods used to deliver and feed babies, alongside the extensive use of antibiotics are some of the most studied determinants in the loss of the intestinal microbial diversity. And so is industrialization: The now limited contact with the countryside, with animals, and the extensive sanitation of the living environment are typical elements of industrialized societies and known causes for the reduced exposure to beneficial microorganisms. Food and its constituents, such as fibres, vitamins, and phenolic compounds, are also crucial to the modulation of intestinal microbial diversity. Not only that, but food, which has undergone a fermentation process, has even been demonstrated to be a vehicle for microorganisms. This, combined with a strong demand for plant-based fermented products, pushed us into the development of a novel soy-based fermented product with increased health capacity. A consortium of LAB was isolated from traditional kefir, including Lactococcus lactis subsp. lactis K03, Leuconostoc pseudomesenteroides K05, L. mesenteroides K09, and Lentilactobacillus kefiri K10. The strains exhibited fermentation capabilities in a soy-based beverage, resulting in acidification and improved texture. L. pseudomesenteroides K05 demonstrated potential for soy isoflavone deglycosylation and exhibited the highest estrogenic-like activity in the fermented product. Finally, while research is available which substantiates how fermented foods contribute their microbiological quote to the human GI tract, little is known about unfermented foods. We thus started investigating the impact of varying cultivation methods on the microbial diversity of ready-to-eat rocket salads to then assess if, and how, the associated bacteria survive the digestive tract. Surprisingly, bacterial load and diversity were comparable among land-based cultivation methods and were generally larger than vertical farming. Most notably, viable LAB was absent in vertical-farmed rocket salad, while land-based rocket salads harboured LAB between 102 and 105 CFU/g. In vitro experiments revealed the ability of rocket salad- associated bacteria to survive the human GI tract. Human interventional studies emphasized the importance of initial bacterial load in detecting viable LAB, post-consumption, in faeces. These findings highlight the potential of food-associated microbes to survive the human digestive tract and persist within the human gut.