Effect of ultrasound on the activity and structure of polyphenol oxidase purified from mango (Mangifera indica cv. "Xiaotainong")

This study separated, purified, and identified mango polyphenol oxidase (PPO) in Xiaotainong mango, and the inactivation effect and possible inactivation mechanism of mango PPO by ultrasound (US) was investigated. The purified mango PPO, identified as Alfonso mango chloroplast PPO (NCBI number: XP:044462061.1), exhibited specific enzyme activity of 178,192 U/mg, with a yield of 1.2%, which was 9.85-fold higher than crude enzyme solution. Bioinformatics analysis of XP_044462061.1 indicated that the PPO consisted of a stable hydrophilic protein with a molecular weight of 66.77 kDa, an amino acid number of 593, and a structural domain similar to the TYROSINASE_1 (PS00497, tyrosinase) CuA and TYROSINASE_2 (PS00498; tyrosinase) CuB binding regions. The result showed that increased US treatment intensity and time better facilitated PPO inactivation, with a higher US intensity performing better than extended treatment time. US changed and disrupted the secondary and endogenous hydrophobic structures of the mango PPO, altered the exogenous hydrophobicity, and caused PPO molecule aggregation, ultimately leading to PPO inactivation. This article provided a theoretical basis for the application of US technology for processing mango products.