Subin Hwang¹, Kun-Ho Seo², Hyunsook Kim^1,

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—specifically Lentilactobacillus kefiri DH5, a phenolic-transforming LAB that remains underexplored relative to commonly used L. plantarum—to enhance polyphenols/antioxidant capacity in Cucumis melo L. byproducts (whole residue vs. juice-derived sludge). We compared sonication, microwave, and citric-acid pretreatments—each with/without subsequent fermentation—to 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–treated 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.

bioconversion, antioxidant activity, polyphenols, Cucumis melo L. byproduct, Lentilolactobacillus kefiri