Effect of fermentation time on the physical, nutritional and mineral properties of cowpea flour subjected to solid-state fermentation with Pleurotus ostreatus

Solid-state fermentation (SSF) is a promising strategy to improve the nutritional quality of legumes, although the influence of fermentation time on these modifications remains poorly understood. This study investigated the effect of fermentation time on the physicochemical properties, phenolic compound, phytic acid content and mineral content of cowpea (Vigna unguiculata) flour fermented with Pleurotus ostreatus. Autoclaved cowpea grains were inoculated with a fungal suspension (264 mg dry biomass mL⁻¹) and fermented for 5, 10, 14, and 21 days, generating samples FCP-5, FCP-10, FCP-14, and FCP-21, while autoclaved flour (A-CF) was used as the control. After fermentation, the samples were dried (60 °C, 48 h), milled, and evaluated for color, total phenolic compounds, antioxidant activity (ABTS, FRAP and ORAC) and mineral content (Fe, Zn, and Mn). Fermentation time markedly influenced all evaluated properties. Progressive darkening of the flour was observed, with lightness (L*) decreasing from 76.68±0.46^b (FCP-5) to 60.12±0.74^b (FCP-21), accompanied by increases in the a* (3.25±0.56^b–9.03±0.25^b) and b* (18.06±0.41^b –26.02±0.73^b) coordinates, reflecting fungal growth and biochemical transformations during SSF. Total phenolic compounds increased approximately fivefold, from 4.09±0.81^a to 21.15±0.66^d mg GAE g⁻¹, with a pronounced increase after 14 days of fermentation. The phytic acid content decreased progressively during fermentation, dropping from 6.70 ± 1.25^a mg/g to 2.05 ± 1.03^d mg/g after 21 days. This result may be associated with phytase production by the fungus, which could contribute to improving the digestibility of this food matrix. The longest fermentation period (21 days) also resulted in higher mineral contents, with increases of 26% in iron, 18% in zinc, and 26% in manganese compared with the control, suggesting enhanced mineral availability during fermentation. 

The marked rise in phenolic compounds after 14 days suggests that this period may represent an important transition in the biochemical modifications promoted by the fungus. Overall, controlling fermentation time provides an effective strategy for tailoring the functional and nutritional properties of fermented cowpea flour. The authors would like to thank the “Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil” (CAPES) (Finance Code 001), the Brazilian National Council for Scientific and Technological Development I.N.F.S fellowship and financial support (CNPq, Productivity Grant [302172/2025-4]) and São Paulo Research Foundation (FAPESP) for financial support (2024/13091-9; 2025/05241-3; 2025/16368-4).