FERMENTATION OF CALENDULA, ECHINACEA AND MALVA OFFICINAL PLANT EXTRACTS AS A MEANS OF INCREASING THEIR SENSORY, ANTIOXIDANT, ANTIMICROBIAL AND NUTRACEUTICAL PROPERTIES

Plants are well known sources of bioactive compounds and of indigenous microflora, that can have beneficial effects on human health. Fermentation is an ancient food technology, still today subject of study and improvement, that can enhance sensory, organoleptic, nutritional quality and shelf-life of products. Moreover, fermentation of plant-based extracts can improve antioxidant activity and bioaccessibility of natural bioactive compounds, as well as reduce antinutritional components and toxic substances in plant foods. In this research project, three plant extracts were used for fermentation tests with microorganisms capable of developing on these substrates. Aqueous extracts of Calendula officinalis, Echinacea purpurea and Malva sylvestris were prepared and separately inoculated with Lactiplantibacillus plantarum 299V, Pediococcus acidilactici 12B, Lacticaseibacillus rhamnosus GG and Bacillus subtilis natto. Appropriate pasteurization treatments, inoculum levels and fermentation conditions were developed. Extracts before and after the fermentation were evaluated for the presence of new properties or potentially beneficial molecules, especially in terms of microbial count, acidity, sugars, organic acids, proteins, minerals, poliphenols, tannins, vitamins, total phenolic compounds and antioxidant activity. In all plant extracts lactic acid bacteria grew well, increasing their populations by more than 3 log, and inducing a decrease of about two pH units. An increase in some minerals was observed in fermented extracts of all three plants in comparison to the non-fermented controls. Total phenolic compounds and antioxidant activity increased in fermented extracts of Echinacea and Malva in comparison to the non-fermented ones, while no significant differences were detected in Calendula extracts. In all three fermented extracts a decrease in glucose and fructose and a consequent lactic and acetic acid production were observed. The results obtained encourage further studies on the possibility to use such fermented extracts in the production of nutraceutical postbiotic foods.