Sustainable valorization of cupuaçu biomass through solid-state fermentation for obtaining antioxidant-rich extracts

By-products generated during the extraction of oils from Amazonian nuts represent an important source of agro-industrial residues that can potentially be converted into high value-added bioactive products. Among these residues, cupuaçu (Theobroma grandiflorum) biomass represents a promising source of phenolic compounds and other bioactive molecules. This study aimed to investigate whether solid-state fermentation (SSF) with the filamentous fungus Rhizopus oryzae could enhance the bioactive potential of cupuaçu biomass. The cupuaçu biomass was subjected to SSF using R. oryzae. Samples were collected at 0h (unfermented control) and after 8h of fermentation. Subsequently, ethanolic extracts were obtained by ultrasound-assisted extraction (UAE) using 80% ethanol and designated as EEC (ethanolic extract of unfermented cupuaçu biomass) and EEC-F (ethanolic extract of fermented cupuaçu biomass). Total phenolic content was determined using the Folin–Ciocalteu method, while antioxidant activity was evaluated by DPPH and ABTS radical scavenging assays. Cytotoxic activity was investigated using the MTT cell viability assay in human prostate cancer cells with bone metastatic origin (PC-3), exposed to different extract concentrations. Comparisons between 0 h and 8 h samples were performed to assess the influence of fermentation on the biological properties of the biomass. Fermentation for 8 h enhanced the bioactive properties of cupuaçu biomass compared with the unfermented sample. Total phenolic content increased from 27,90 ± 1,24 GAE/g in EEC to 41,63 ± 1,73 mg GAE/g in EEC-F. Antioxidant activity was also improved after fermentation, with DPPH values of 0,51 ± 0,12 μmol TE/ g in EEC and 1,01 ± 0,07 μmol TE/ g in EEC-F. Consistently, EEC-F exhibited higher antioxidant activity in ABTS, with 1,80 ± 0,23] μmol TE/ g, compared with EEC (1,34 ± 0,13 μmol TE/ g). In the MTT assay, both EEC and EEC-F reduced PC-3 cell viability in a dose-dependent manner, although EEC-F exhibited a stronger cytotoxic effect at both exposure times, achieving approximately 30% reduction in cell viability at a lower concentration than EEC. These findings indicate that the SSF with R. oryzae improved the antioxidant and cytotoxic properties of residual cupuaçu biomass, demonstrating the potential of this bioprocess as a sustainable strategy for the valorization of Amazonian agro-industrial by-products and the recovery of compounds with potential biological applications. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001.