The production and characterization of probiotic bacterial metabolites through tapioca starch fermentation

Postbiotics refer to biomolecules produced and released by living bacteria, such as enzymes, peptides, teichoic acids, peptidoglycan-derived muropeptides, polysaccharides, cell surface proteins, and organic acids. In recent years, the use of microbial-derived biomolecules, called "postbiotics", as an alternative to the use of live probiotic microorganisms, is one of the subjects of great interest. In this thesis, the bioactive properties of postbiotic products produced by Lactobacillus plantarum, as one of the dominant probiotic bacteria that can colonize the human intestinal mucosa, were investigated by focusing on how prebiotic tapioca starch, as a natural source of resistant starch, can affect the probiotic activity of L. plantarum when used alone and in combination with skim milk powder. Our results show that the combined use of tapioca starch and skim milk promotes the anti-bacterial effects of the L. plantarum post-fermentation medium on the pathogens Pseudomonas aeruginosa and Klebsiella pneumonia as well as anti-cancer activities on colon cancer cells. In the thesis, the use of Fourier-Transform Infrared Spectroscopy (FTIR) technique allowed us to identify the molecular changes in the post-fermentation medium obtained from the L. plantarum grown in the presence of tapioca resistant starch or skim milk alone or in combination. Diet is recognized as one of the main drivers of microbiota composition, diversity, and function. The production of functional foods containing prebiotic ingredients is a promising market with the potential to dominate the food industry. In this aspect, this thesis is important in demonstrating that the biofunctionality of L. plantarum postbiotics can be modulated through low-cost and easily accessible food sources and natural and "clean label" food ingredients: tapioca resistant starch and skim milk powder.