Lactic fermentation for the valorisation of plant by-products: new substrates and novel applications

Economic development requires a large amount of raw materials, which are quickly consumed. In the agro-food industry, a significant quantity of by-products and/or waste is also produced, resulting in approximately one-third of food production being wasted. Agroindustrial biomasses are often characterised by high water content and chemical composition in fibers, proteins and bioactive compounds, making them matrices suitable for numerous applications. The nutrients present in waste matrices can be an excellent growth substrate for microorganisms. Through the fermentation process, these microorganisms can convert or produce molecules of industrial interest, which is why fermentation has attracted increasing interest. These final products could include bioactives, like antimicrobial agents, antioxidants, volatile compounds, organic acids and deglycosylated polyphenols. Fermentation offers several advantages, including low costs, minimal energy and water consumption, and the ability to convert by-products and waste into high-value products. Lactic fermentation, in particular, is carried out by lactic acid bacteria, microorganisms which are considered GRAS (Generally Recognised As Safe) by Food and Drug Administration (FDA) or with the Qualified Presumption of Safety (QPS) status by European Food Safety Authority. Due to their simple metabolism, characterised by a high nutrient intake and resistance to stress, such as acidic environments and high temperatures typically encountered in industrial process, their potential as cell factories for the chemical industry is being increasingly explored. With this knowledge, the thesis has been focused on the valorisation of different plant matrices through the application of lactic acid fermentation followed two lines. The first one was to evaluate the changes on molecular profile of two by-products which may be relevant in our agro-industrial sector, like Okara and Opuntia Ficus Indica Cladodes. The second line involved the possible application of an extract with antimicrobial activity, obtained from the lactic fermentation of tomato peels and seeds, in a production process.