Phytochemical composition and bioactivities of Turkish walnut (Juglans regia L.) septum extracts

Abstract

Walnut (Juglans regia L.) septum (WS) is an underutilised by-product despite its rich phytochemical potential. In this study, WS extracts obtained by water and CO₂-assisted extraction were phytochemically characterised, and their antioxidant, antimicrobial, and enzyme inhibitory activities were systematically evaluated. The WS extracts contained a diverse phenolic profile, with vanillic acid (17.13-53.62 µg/g) and quercetin (14.96-16.53 µg/g) identified as the predominant compounds. The extracts exhibited high total phenolic (10.56–11.05 mg GAE/g) and flavonoid contents (27.92–32.42 mg QE/g), which were reflected in their strong antioxidant capacities. Notably, WS extracts demonstrated potent radical scavenging activity, with IC₅₀ values ranging from 0.15 to 0.34 mg/mL, along with high ferric reducing power (approximately 38.5 mg TE/mL). In addition to antioxidant activity, the extracts showed marked biological functionality. The CO₂-assisted extract displayed enhanced α-amylase inhibitory activity (IC₅₀: 0.96 mg/mL), indicating notable antidiabetic potential, whereas the aqueous extract exhibited broader antimicrobial efficacy, particularly against Candida albicans and Saccharomyces cerevisiae. Overall, these findings highlight WS as a valuable natural source of bioactive compounds with significant antioxidant, antimicrobial, and enzyme inhibitory properties, supporting its potential use in functional food and nutraceutical applications.