Abstract
Aflatoxin M(1) (AFM(1)) in milk poses a significant threat to human health. This study examined the capacity of Bacillus licheniformis CotA laccase to oxidize AFM(1). The optimal conditions for the CotA laccase-catalyzed AFM(1) oxidation were observed at pH 8.0 and 70 °C, achieving an AFM(1) oxidation rate of 86% in 30 min. The Km and Vmax values for CotA laccase with respect to AFM(1) were 18.91 μg mL(-1) and 9.968 μg min(-1) mg(-1), respectively. Computational analysis suggested that AFM(1) interacted with CotA laccase via hydrogen bonding and van der Waals interactions. Moreover, the oxidation products of AFM(1) mediated by CotA laccase were identified as the C3-hydroxy derivatives of AFM(1) by HPLC-FLD and UPLC-TOF/MS. Toxicological assessment revealed that the hepatotoxicity of AFM(1) was substantially reduced following oxidation by CotA laccase. The efficacy of CotA laccase in removing AFM(1) in milk was further tested, and the result showed that the enzyme agent achieved an AFM(1) removal rate of 83.5% in skim milk and 65.1% in whole milk. These findings suggested that CotA laccase was a novel AFM(1) oxidase capable of eliminating AFM(1) in milk. More effort is still needed to improve the AFM(1) oxidase activity of CotA laccase in order to shorten the processing time when applying the enzyme in the milk industry.