eng Science and Education Publishing Journal of Food and Nutrition Research 2333-1240 2025-11-27 13 11 421 427 10.12691/jfnr-13-11-2 JFNR202513112 article Subin Hwang 1 Kun-Ho Seo 2 Hyunsook Kim hyunsk15@hanyang.ac.kr 2 Department of Food & Nutrition, College of Human Ecology, Hanyang University, Seoul 04763, South Korea Center for One Health, Department of Veterinary Public Health, College of Veterinary Medicine, Konkuk University, Seoul 05029, South Korea Conventional physicochemical pretreatments (ultrasound, microwave, mild-acid hydrolysis) can require high energy/heat and lack specificity, risking degradation of heat-sensitive phytochemicals and uncontrolled alterations in composition. To address these limitations, we evaluated microbial bioconversion¡ªspecifically Lentilactobacillus kefiri DH5, a phenolic-transforming LAB that remains underexplored relative to commonly used L. plantarum¡ªto enhance polyphenols/antioxidant capacity in Cucumis melo L. byproducts (whole residue vs. juice-derived sludge). We compared sonication, microwave, and citric-acid pretreatments¡ªeach with/without subsequent fermentation¡ªto bioconversion alone. Fermentation of untreated whole residues (NB) produced the largest gains in total polyphenols and the highest DPPH scavenging activity, outperforming physicochemical pretreatments and even sonication-assisted fermentation; citric-acid pretreatment showed no benefit. Representative values include NB DPPH 82.56% vs. 66.6% in untreated controls; citric-acid¨Ctreated samples failed to improve even after bioconversion. Sludge (juice residues) showed limited responsiveness, consistent with substrate depletion after juicing. In conclusion, selective, enzyme-driven L. kefiri DH5 bioconversion resolves prior extraction limitations and maximizes bioactivity without harsh processing, positioning Cucumis melo L. byproducts as promising prebiotic-oriented ingredients. https://pubs.sciepub.com/jfnr/13/11/2/jfnr-13-11-2.pdf bioconversion antioxidant activity polyphenols Cucumis melo L byproduct Lentilolactobacillus kefiri