Microalgae- and bacteria-mediated valorization of fruit processing byproducts/wastes in a green, circular economy perspective

Different companies process pear, apple, peach and apricot fruits to produce juice, puree, or other types of products generating high amounts of byproducts/wastes. These companies currently face the need to reduce waste treatment direct costs. In fact, the industrial processes for fruit transformation produce great amounts of organic byproducts/wastes, usually referred as pomaces, with residues of peels, seeds, pulp and/or stem (in this project named FPM, Fruit Processing Matrices). The common management methods of FPM such as landfilling, anaerobic digestion or feed supplementation are not sustainable since they are not cost-effective and can cause environmental pollution and even public health hazards. On the other hand, FPM have considerable amounts of sugars and other nutritional compounds and offer great potentials in terms of sustainable resource recovery with circular bioeconomy goals but are currently underutilized. Valorization of FPM includes biological methods, which are often based on the use on fungi and to a lesser extent on bacteria, while the use of microalgae is limited to those capable of mixotrophic or heterotrophic metabolism. Furthermore, biological valorization of FPM usually suffers the presence of micro-organisms-inhibiting molecules, such as phenolics or residues of agrochemicals. With these premises, ALBA-VITA aims to evaluate the suitability of FPM extracts as substrates/additives for bacterial and microalgal growth and the obtainment of biobased products such as pigments, phenolic compounds, long-chain polyunsaturated fatty acids (LC-PUFAs) and antimicrobial compounds. For this goal, aqueous extracts (AE) of different FPM recovered from local food processing companies will be prepared, and their composition will be characterized by NMR spectroscopy. Based on the NMR results, AE will be subjected to appropriate treatment (dilution in culture media and/or addition of mineral nutrients) and used for microalgae and bacterial growth. For bacteria, also the solid fraction remaining after AE preparation will be used. From this first screening, the most suitable substrate and promising microbial isolates will be selected. The soluble components of microalgae and bacteria biomass including pigments, LC-PUFAs, phenolic compounds and other classes of compounds will be recovered by extraction with different solvents and characterized by NMR and UHPLC-MS. Moreover, cell-free culture supernatants (CFS) will be analyzed by NMR and UHPLC-MS to monitor the consumption of nutrients of FPM origin and to characterize the products released by microalgae and bacteria. Finally, antimicrobial activity of all extracts and CFS towards representative species of plant pathogenic fungi and bacteria will be evaluated. The results of the project have the ambition to provide knowledge on algal and bacterial valorization of FPM into value-added biobased products with potential application in controlling harmful microbes for plants or other sectors.