Solid-State Fermentation of Corn Silk by Aspergillus niger Improves Phenolic Profile and Antioxidant Capacity

Corn silk (CS), a residue of maize cultivation, represents an underutilized source of bioactive compounds, particularly phenolics. In this context, the present study investigated the effect of solid-state fermentation (SsF) using Aspergillus niger ATCC-6275 on increasing the phenolic profile and antioxidant activity of CS over a 10-day period. Total phenolic and flavonoid contents increased by approximately 73% and 37%, respectively. HPLC-DAD-ESI-MS analysis revealed substantial enrichment of hydroxycinnamic acids, particularly 4-caffeoylquinic (20-fold), 5-synapoylquinic (9-fold), and 4-feruloylquinic (5-fold) acids, suggesting enzymatic release of bound phenolic compounds. Enzymatic hydrolysis of flavonoid glycosides resulted in aglycone accumulation, such as methoxyluteolin and luteolin. The antioxidant activity of fermented CS significantly improved, with DPPH, ABTS, and FRAP assays indicating increases of 23%, 50%, and 44%, respectively. These biochemical transformations occurred alongside organic acid production and sugar depletion, confirming active fungal metabolism. Overall, this work supports SsF as an eco-friendly strategy for converting corn silk into a high-value functional ingredient for food, pharmaceutical, or nutraceutical applications.