Characterization and assessment of nutraceutical properties of officinal plants subjected to bacterial fermentation

Medicinal plants are well-known sources of bioactive compounds and indigenous microflora that confer numerous health benefits. Fermentation is an ancient food technology, which remains a subject of extensive study due to its capacity to enhance the sensory, organoleptic, and nutritional properties of products while extending their shelf-life. Additionally, the fermentation of plant-based extracts can improve the antioxidant activity and bioavailability of natural bioactive compounds, as well as reduce antinutritional components and toxic substances commonly present in plant foods. In today’s market, facing the increasing consumer demand for food products that not only provide health benefits but also have the potential to reduce the risk of disease, fermentation of medicinal plant extracts may offer a promising approach to enhance their phytochemical profile and boost functional properties. This thesis aimed to investigate the potential of Malva sylvestris, Calendula officinalis, and Echinacea purpurea aqueous extracts fermented with selected bacterial strains, specifically Lactiplantibacillus plantarum 299V, Pediococcus acidilactici IRZ12B, Lacticaseibacillus rhamnosus GG, and Bacillus subtilis natto. Appropriate plant-bacteria combinations, pasteurization treatments, inoculum levels, and fermentation conditions were developed. The extracts, both before and after fermentation, were analyzed in terms of microbial counts, acidity, sugars, organic acids, proteins, minerals, polyphenols, tannins, vitamins, and total phenolic content. Functional properties were assessed in terms of antioxidant, antimicrobial, and antiproliferative activities. Specifically, for antimicrobial analysis, the growth curves of human pathogens, including Escherichia coli CFA-i, Salmonella enterica SL1344, and Yersinia enterocolitica Xen24 were evaluated following exposure to the plant extracts. As regards antiproliferative analysis, apoptotic damage on colon adenocarcinoma cells Caco-2 was quantified, along with the investigation of cell death mechanisms. Results revealed that the tested bacteria thrived in all the herbal matrices, in some cases leading to an enhancement of the phytochemical profile and improving functional properties. Outcomes underline the potential of microbial fermentation as a biotechnological tool to boost the health-promoting properties of medicinal plants. Findings of this thesis regarding bacterial fermentation, especially by lactic acid bacteria strains, of malva, calendula, and echinacea aqueous extracts offer promising perspectives for future research and industrial applications, encouraging further studies on the incorporation of such fermented extracts into functional food products.