Enhancement of Antioxidant and Anti-Inflammatory Activities of Radish (Raphanus sativus L.) By-Products Through Enzymatic Pretreatment and Lactic Acid Fermentation

Radish (Raphanus sativus L.) is an important vegetable resource in the food industry, generating substantial amounts of by-products during cultivation and distribution. Despite their richness in functional components, these by-products are largely underutilized. Accordingly, there is increasing interest in their valorization as functional food ingredients. This study evaluated the functional potential of radish by-products removed prior to distribution by applying cellulase pretreatment and Lactiplantibacillus plantarum fermentation individually or in combination. Radish samples were separated into leaf blade, stem, and taproot tissues and processed as untreated control, enzyme-treated, fermented, and enzyme-treated and fermented (EF) groups. The EF treatment significantly increased reducing sugar content, total polyphenols, and total flavonoids across all tissues, with the most pronounced enhancement observed in leaf by-products. In antioxidant assays, EF samples showed decreased IC50 values in DPPH and ABTS radical scavenging assays and increased FRAP values, indicating superior antioxidant capacity. In lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages, EF-treated leaf extracts effectively suppressed nitric oxide and intracellular ROS production without cytotoxicity and exhibited the highest GSH/GSSG ratio, suggesting improved cellular redox balance. In contrast, interleukin-6 (IL-6) secretion varied depending on tissue type and processing condition, indicating that antioxidant enhancement does not necessarily correspond to uniform cytokine regulation. Collectively, these findings demonstrate that enzymatic pretreatment combined with lactic acid fermentation serves as an effective strategy to enhance the antioxidant and cell-protective properties of radish by-products, supporting their potential use as value-added functional food ingredients.