Valorization of Malaysian agro-industrial by-products: A comparative study of antioxidant properties in standardized NaDES-polyphenol enriched extracts

Abstract

Oxidative stress is an imbalance between free radical generation and endogenous antioxidant defences is a key contributor to chronic diseases such as cancer, metabolic disorders, and cardiovascular conditions. Polyphenolic compounds from plants and agro-industrial by-products are recognized for their strong antioxidant properties; however, their wider application remains limited by variability in polyphenol content, inefficient extraction methods, and the lack of standardized analytical approaches. This study aims to address these challenges by comparing and correlating the antioxidant potential of standardized NaDES–polyphenol enriched extracts derived from selected underexplored Malaysian commodity crop by-products. Natural deep eutectic solvents (NaDES) combined with ultrasound-assisted extraction were employed to obtain polyphenol-rich extracts, which were quantified for total phenolic content (TPC) and total flavonoid content (TFC). Antioxidant activities were evaluated using rapid colorimetric assays, including DPPH, ABTS, nitric oxide (NO) scavenging, and ferric reducing antioxidant power (FRAP). Chemometric analysis using partial least squares–discriminant analysis (PLS-DA) was applied to determine correlations between polyphenolic profiles, extraction solvents, and antioxidant responses. NaDES-extracted samples consistently exhibited higher TPC and TFC compared to aqueous extracts, demonstrating the superior solubilization and extraction efficiency of NaDES. Strong positive correlations were observed between TPC/TFC and all antioxidant assays, confirming the reliability of these rapid methods for screening antioxidant potency. PLS-DA revealed distinct clustering based on extraction solvents, indicating their influence on polyphenolic composition and bioactivity. Overall, this study highlights the untapped potential of Malaysian commodity crop by-products as sustainable sources of natural antioxidants and underscores the effectiveness of NaDES as a green and efficient extraction strategy for polyphenol recovery.