Grape marc biotransformation to protein-rich food ingredients using fungal fermentation

The increasing global population and rising environmental and nutritional demands require sustainable, alternative protein sources. This study explores the biovalorization of grape marc, a by-product of winery and distillery industries, as cultivation medium for edible filamentous fungi to produce protein-rich biomass for food applications. Three fungal strains, Neurospora intermedia, Aspergillus oryzae, and Rhizopus oryzae, were cultivated at three scales: shake flasks, bench-scale (4.5 L), and demo-scale (1300 L) bubble column reactors. Hydrothermal pretreatment (121 °C, 20 min) was applied to grape marc (GM) prior to fermentation under varying GM concentrations (2–8 % w/v), pH (3.88–6), cultivation times (48–72 h), and supplementation (vitamins, trace metals, yeast extract). The fungal biomass was analyzed for physicochemical properties, crude protein and fat, amino acid and fatty acid profiles, minerals, and polyphenols. The fungal biomass yields reached up to 4.4 g dry weight/L, with crude protein contents up to 60 % dry weight, notably with N. intermedia. Fungal biomass exhibited a complete essential amino acid profile, with high leucine and lysine levels, along with favorable fatty acid, minerals and polyphenols. This study demonstrates the feasibility of producing sustainable, protein-rich fungal biomass from GM, offering a valuable solution for food applications within a circular bioeconomy.