BIOACTIVE COMPOUNDS FROM UNFERMENTED AND FERMENTED GRAPE JUICE PROCESSING WASTE

Waste generation is a global challenge, particularly affecting agro-industrial producers such as Brazil. In 2024, Brazilian grape juice exports increased by 22% compared to previous years, reflecting the country’s growing production. Waste from juice processing can serve as raw material for new products and processes, thereby reinforcing circular economy strategies. Grape wastes are rich in bioactive compounds, including polyphenols with recognized antioxidant activity, as well as macromolecules and minerals that can act as substrates for Solid-State Fermentation (SSF). This process can generate or enhance the concentration of bioactive molecules. The aim of this study was to quantify the polyphenol content in grape wastes from juice processing of four genotypes (‘Bordô’, ‘Magna’, ‘Niagara Rosada’, and ‘Violeta’) and to use them as substrates for SSF with fungi of the genus Aspergillus spp. The objective was to assess the increase in bioactive availability and evaluate the antioxidant capacity of unfermented and fermented grape wastes. Immediately after juice production, wastes were collected and stored at –20 °C. Unfermented samples were homogenized in a mixer and freeze-dried at –60 °C for 48 h. Fermented samples were homogenized, weighed into bioreactors, inoculated with spores of A. niger and A. oryzae, and incubated at 30 °C for 168 h, followed by freeze-drying at –60 °C for 48 h. Analyses were performed for total phenols, flavonoids, and antioxidant activity using the DPPH, ABTS, FRAP, and MDA assays. Data were tested for homoscedasticity (Bartlett) and normality (Shapiro-Wilk), followed by ANOVA and Tukey for significance and mean comparison. Fermented grape wastes showed higher total phenol levels than unfermented ones, with Magna + A. oryzae reaching the highest (395.99 mg GAE/g). Total flavonoid levels also increased after fermentation in Bordô and Magna wastes, with Bordô fermented with A. niger showing the highest value (18.11 mg QE/g). Among unfermented samples, Niagara Rosada demonstrated strong antioxidant activity, with 89.3% DPPH radical scavenging and 241.31 mM TE/g in the ABTS assay. In the FRAP assay, all fermented samples outperformed unfermented ones, with Magna fermented with A. niger achieving the highest activity (631.48 mM reduced Fe/g). In the MDA assay, Niagara Rosada wastes fermented with A. niger and A. oryzae produced the lowest levels of malondialdehyde, indicating superior antioxidant capacity. Despite undergoing heat treatment during juice production, grape wastes still retain significant bioactive compounds. Their use in SSF enhances the bioavailability of these compounds, which can be recovered and incorporated into biotechnological applications.