Dityrosine-Lowering Lactiplantibacillus plantarum HNGD-XJ9: Screening, Characterization, and Evaluation

Dityrosine, a specific protein oxidation product formed through oxidative crosslinking of tyrosine residues, accumulates in foods and is associated with potential health risks. The removal of pre-existing dityrosine from food matrices remains a significant challenge. Given the metabolic versatility of lactic acid bacteria (LAB) in amino acid catabolism, they may provide a promising biological solution for this problem. In the present work, a food-grade LAB with high dityrosine-lowering activity was screened from naturally fermented food isolates through targeted screening. Among 1213 presumptive LAB strains, HNGD-XJ9 exhibited the highest reduction efficiency and was identified as Lactiplantibacillus plantarum by phylogenetic, morphological, and whole-genome ANI analyses. The strain exhibited favorable gastrointestinal tolerance, notable adhesive properties, and no hemolytic activity, indicating its in vitro probiotic-related properties. Whole-genome sequencing revealed candidate genes involved in aromatic amino acid metabolism and aromatic ring cleavage, providing molecular insights into its putative mechanism for dityrosine reduction and offering genomic clues for further investigation of its probiotic-related properties. Fermentation with HNGD-XJ9 significantly reduced detectable dityrosine levels by 70.89% in spray-dried milk powder and 58.61% in roasted pork powder (p < 0.05), along with decreases in other oxidative markers and partial restoration of protein conformational integrity. These results suggest that HNGD-XJ9 is a promising strain for mitigating dityrosine accumulation in foods and for developing functional foods with lower protein oxidation-related risks.