Review of high-value food waste and food residues biorefineries with focus on unavoidable wastes from processing

Processing of food is linked to unavoidable and inedible food waste that, despite efforts to minimize waste, will persevere. It nevertheless represents a stable feedstock for the future bioeconomy value chains and products. This study presents a systematic review of 149 examples from the scientific literature using inedible, unavoidable food residues and wastes for the production of value-added bio-based compounds that could substitute synthetic chemicals production. The main high-value products investigated are organic acids, bioplastics, colorants, enzymes and other platform chemicals. We found 44 examples of acid production with high variability in output (from 43 to 640 g kg(-1) waste), 9 examples of bioplastics (from 0.28 to 49 g L-1), 26 examples related to colorants (from 0.04 to more than 400 mg per 100 g), 22 cases of enzyme production (from 6000 Ug(-1)), 4 examples of protein (23.6 to 38.5 %wt. DM) and 44 cases of other high-value molecules such as pectin and single cell oils. Our findings highlight fermentation as a key technology for the valorization of the studied feedstock, with 76 examples out of the 149 reviewed. The review process also uncovered important limitations related to the lack of standardized food waste definitions, a barrier that is discussed and for which solutions are proposed. At the light of our findings, we further proposed guiding criteria towards the sustainable development of future biorefineries based on food waste. This work touches upon several Sustainable Development Goals, in particular goals 8.2, 9.5, and 12.3.