Multicopper Oxidase from Lactobacillus hilgardii: Mechanism of Degradation of Tyramine and Phenylethylamine in Fermented Food

Elevated levels of biogenic amines (BAs) in fermented food can have negative effects on both the flavor and health. Mining enzymes that degrade BAs is an effective strategy for controlling their content. The study screened a strain of Lactobacillus hilgardii 1614 from fermented food system that can degrade BAs. The multiple copper oxidase genes LHMCO¹⁶¹⁴ were successfully mined after the whole genome protein sequences of homologous strains were clustered and followed by homology modeling. The enzyme molecules can interact with BAs to stabilize composite structures for catalytic degradation, as shown by molecular docking results. Ingeniously, the kinetic data showed that purified LHMCO¹⁶¹⁴ was less sensitive to the substrate inhibition of tyramine and phenylethylamine. The degradation rates of tyramine and phenylethylamine in huangjiu (18% vol) after adding LHMCO¹⁶¹⁴ were 41.35 and 40.21%, respectively. Furthermore, LHMCO¹⁶¹⁴ demonstrated universality in degrading tyramine and phenylethylamine present in other fermented foods as well. HS-SPME-GC-MS analysis revealed that, except for aldehydes, the addition of enzyme treatment did not significantly alter the levels of major flavor compounds in enzymatically treated fermented foods (p > 0.05). This study presents an enzymatic approach for regulating tyramine and phenylethylamine levels in fermented foods with potential applications both targeted and universal.