Flavonoid production via solid-state fermentation of agro-industrial waste with biopesticidal fungi: screening, optimization and scale-up.

Flavonoids are bioactive compounds with significant applications in agriculture due to their antimicrobial properties, ability to mitigate abiotic stress and role in promoting plant-microbe interactions. This study explores the potential of producing flavonoids through solid-state fermentation (SSF) using agro-industrial residues as substrates for filamentous fungi. Trichoderma harzianum, Trichoderma viride and Beauveria bassiana were evaluated for their ability to increase total flavonoids content on different substrates, in a screening process at laboratory scale, achieving a production of 0.53 ± 0.09 mg of total flavonoids per gram of dry matter (mg g−1dm) with T. harzianum in a blend of 30% spent coffee grounds (SCG) and 70% brewers spent grain (BSG) as carbon source. Subsequently, the bioprocess was optimized on 0.5 L packed bed bioreactors regarding cultivation time and productivity. A design of experiments was conducted to evaluate the influence of substrate composition and moisture content on the production of the desired metabolites, as well as the effect of temperature variation, resulting in an increase in total flavonoid production to 0.75 ± 0.14 mg g−1dm. Finally, the process was scaled-up under optimized conditions in a 22 L packed bed bioreactor, reaching a production of 0.43 ± 0.07 mg g−1dm. These results demonstrate the feasibility of valorizing agro-industrial residues through SSF using biopesticidal fungi, providing a scalable bioprocess to produce flavonoid-rich bioinputs.