Screening and functional characterization of purine-degrading Limosilactobacillus fermentum R-9 and its active enhancement effect in the fermentation of Smilax glabra Roxb

Hyperuricemia is associated with dietary purine intake, dysregulated purine metabolism, and impaired uric acid excretion. This study aimed to isolate multifunctional LAB from fermented foods and apply the selected strain to enhance the functional potential of Smilax glabra Roxb. fermentation. Among 79 isolates, 46 were identified as LAB. Limosilactobacillus fermentum R-9 showed efficient degradation of inosine, guanosine, and adenosine, while exhibiting favorable gastrointestinal tolerance and safety-related probiotic properties. Its survival rates after simulated gastric and intestinal digestion were 82.28% and 67.18%, respectively. Genomics revealed genes related to nucleoside hydrolysis, purine/pyrimidine transport, nucleotide salvage, starch utilization, α-glucan metabolism, and β-glucosidase-related glycoside transformation, supporting the dual potential of R-9 for purine metabolism and adaptation to starch-rich S. glabra . L. fermentum R-9 was further used to ferment Smilax glabra Roxb., a starch-rich medicinal and edible plant material containing flavonoid glycosides. After 4 days of fermentation, total phenolics increased from 0.384 to 0.572 mg GAE/mL, and total flavonoids increased from 2.11 to 3.02 mg RE/mL. Xanthine oxidase (XOD) inhibitory activity increased from 16.58% to 70.81%, accompanied by enhanced DPPH and ABTS radical-scavenging activities. Astilbin reached 59.75 μg/mL, increasing by 33.79%. Mechanistically, L. fermentum R-9 fermentation promoted acidification, amylase and β-glucosidase activities, starch matrix disruption, and flavonoid release. These findings highlight L. fermentum R-9 as a promising starter for developing fermented Smilax glabra Roxb. products with enhanced antioxidant and xanthine oxidase inhibitory potential.