Substrate specificity of polyphenol oxidase and its selectivity towards polyphenols: Unlocking the browning mechanism of fresh lotus root (Nelumbo nucifera Gaertn.)

•Two homologous PPOs were identified in lotus root with molecular weights of 56.8 kDa and 67.1 kDa.•Lotus root PPO exhibited highest catalytic activity at 35 ℃ and pH 6.5.•(-)-Epigallocatechin showed lower dock energy and more interactions with PPO than (+)-catechin.•(+)-Catechin entered the active cavity of PPO more quickly due to its smaller structure.•(-)-Epigallocatechin and (+)-catechin are key substrates responsible for lotus root browning.