Abstract
Fermented foods are common throughout the world and for centuries. Recently, lactic acid bacteria revealed a huge potential to combine innovative and traditional applications during food processing. Lactic acid fermentation has been adopted not only for preserving perishable food but also for designing functional food. Being an excellent source of health promoting components and bioactive compounds, fruit, vegetable and their corresponding by-products have attracted considerable interest for their potential applications in food and pharmaceutical field. In this thesis, the exploitation of plant inherent reservoirs was highly achieved through the lactic acid fermentation driving the path of the healthiest metabolic pathways. Firstly, autochthonous lactic acid bacteria (Lactiplantibacillus plantarum AVEF 17) were used as a starter to enrich the portfolio of bioactive compounds of avocado fruit. Fermented avocado puree resulted in high levels of total free amino acids and marked increase of antioxidant activity. The high antioxidant effect was most likely due to bio-converted phenolic compounds and fatty acid derivatives generated by bacterial metabolism. Secondly, apple by-products (AP) were successfully recycled through a designed fermentation by selected autochthonous L. plantarum AFI5 and Lactobacillus fabifermentans ALI6 used singly or as binary cultures with the selected Saccharomyces cerevisiae AYI7. The accumulation of phenolic acid derivatives highlighted the microbial metabolism during AP fermentation. Bio-converted phenolic compounds were likely responsible for the increased DPPH scavenging capacity. The potential health-promoting effects of fermented-AP were in vitro highlighted using Caco-2 cells. With variations among single and binary cultures, fermented-AP counteracted the inflammatory processes and the effects of oxidative stress in Caco-2 cells, and preserved the integrity of tight junctions. Fermentation was also successfully applied to enhance the accessibility of nutrients in bee-collected pollen (BCP). Started-BCP was differentiated by the highest level of esters and alcohols, although volatile free fatty acids were always prevailing. The profile of VOC was dependent on the type of fermentation, which was attributable to Apilactobacillus kunkeei and Hanseniaspora uvarum strains used as starters, or yeasts and bacteria naturally associated to the BCP. Started-BCP and, to a lesser extent, Unstarted-BCP resulted in increased serum-available phenolic compounds, which included microbial derivatives of phenolic acids metabolism. Among the plant based fermented products, sauerkrauts represent the quintessential example of spontaneous fermented food. A conceptual/ecological mechanistic view on how the ecological factors affect the shaping and assembly of microbiomes during cabbage fermentation was proposed. Culture dependent and independent approaches were combined in order to investigate the succession of lactic acid bacteria microbiota. Proper microbial succession during sauerkraut fermentation preserves the nutritive value of cabbage fibers and converts phytochemicals into bioavailable metabolites creating desirable sensory properties. Fermentation process was initiated by Leuconostoc species, followed by Pediococcus species and finally the environment was dominated by Lactobacillus species. The main physico-chemical and biochemical changes occurring during sauerkraut fermentation were investigated, with a focus on chemical metabolites likely affecting microbial population dynamics. The correlation between microbiome and chemical metabolites was determined and gene function prediction indicated the main metabolic pathways. During the last phase of fermentation, Lactobacillus species including L. plantarum showed a high potential of microbial bioconversion, metabolizing hydrocinnamic acids into bioavailable phenolics derivatives and contributing in the production of aroma compounds.