Extrusion and solid-state fermentation with Aspergillus oryzae on the phenolic compounds and radical scavenging activity of pecan nut (Carya illinoinensis) shell

Abstract

Purpose Solid-state fermentation (SSF) has been highlighted as an alternative to obtain valuable compounds using agro-industrial wastes as a substrate. The present study evaluated the impact of extrusion combined with SSF on the production of phenolic compounds and their antioxidant activity using pecan nut shell (PWS) as a substrate. Design/methodology/approach PWS and extruded pecan nut shell (PWSE) were fermented for 120 h at 30°C using Aspergillus oryzae (A. oryzae). Samples were withdrawn from incubator at 6 h, 12 h and then every 12 h until 120 h fermentation. PWS and PWSE samples were extracted. The total phenolic content (TPC) and radical scavenging activity (RSA) extracts were characterized from the resulting extracts. Findings The use of PWSE yielded higher A. oryzae biomass and at a higher rate after 120 h of fermentation (PWS 75.74% vs PWSE 87.50%). In general, the TPC and the RSA increased with fermentation time. However, the PWSE yielded significantly higher (p < 0.05) TPC and RSA values after SSF in comparison to the nonextruded PWS. Condensed tannins showed different trends depending on the fermented substrate. Overall, results showed that the extrusion pretreatment joint with the SSF represents a good alternative to raise the phenolic content and antiradical activity of lignocellulosic materials such as PWSs. Originality/value This study offers valuable information that may be used by the pecan walnut industry to valorize the shell coproduct as a substrate to produce functional ingredients or fungal enzymes.