Characterization of Crude Polyphenol Oxidase Activity in Buckwheat Sprouts

Buckwheat sprouts can not only effectively reduce the trypsin inhibitor in buckwheat grain, but also improve the content of bioactive ingredients such as flavonoids and other effective components. However, Polyphenol Oxidase (PPO) in buckwheat sprouts causes browning of food, which limits the application of buckwheat sprouts in food. In addressing this problem, studying the characteristics of PPO in buckwheat sprouts is necessary. PPO in buckwheat sprouts was first studied by germinating buckwheat sprouts as raw material for 10 days. Results showed that the optimum temperature and pH of PPO in buckwheat sprouts were 32°C and 7.2, respectively. PPO had specificity to substrates. The catalytic capacity of PPO with pyrogallic acid was higher than that of catechol, which had weak catalytic capacity of hydroquinone and resorcinol and no catalytic capacity to gallic acid. PPO showed strong thermal stability because its relative activity remained 23.1%±1.69% even heating at 90°C for 30 min. Ascorbic acid, L-cysteine, sodium hydrogen sulfite and sodium sulfite all had significant inhibition effect on PPO activity. The best inhibitor was ascorbic acid, whereas citric acid and Ethylenediaminetetraacetic acid disodium salt had no evident effect. The PPO activity was inhibited at a low concentration of Cu²⁺ and Mg²⁺ (0-1 mm) and it can be significantly activated at a higher concentration (5-50 mm) by adding AL³⁺, whereas no significance was observed when adding Ca²⁺. This study can provide reliable theoretical support for avoiding browning of buckwheat sprouts during food processing.