Inactivation of polyphenol oxidase by dielectric barrier discharge (DBD) plasma: Kinetics and mechanisms

Cold plasma-induced inactivation of polyphenol oxidase (PPO) in plant-derived foods has been recognized, but the underlying mechanisms are not fully understood. The present study aimed to elucidate the kinetics and mechanisms of PPO inactivation using dielectric barrier discharge (DBD) plasma. The PPO solution (2 mL) was treated with DBD plasma at different times. The results showed that PPO activity decreased by 70.2%, 85.7%, and 94.2% after DBD plasma exposure at 19.4, 26.4, and 32.6 W, respectively, for 3 min. The PPO inactivation curves were well fitted by the Weibull and logistic models. DBD plasma exposure resulted in a significant decrease in the intrinsic fluorescence intensity of PPO, suggesting the disruption of its tertiary structure. Circular dichroism analysis indicated that DBD plasma caused the unfolding of PPO, thereby increasing content of beta-sheets and decreasing the alpha-helices. DBD plasma also induced the oxidative degradation and carbonylation of PPO. After DBD plasma exposure at 26.4 W for 3 min, the surface hydrophobicity of PPO decreased by 60.9%, and the sulfhydryl content declined by 31.2% (p < 0.05). In summary, DBD plasma induced significant changes in the structure and oxidative modification of PPO, which might be responsible for the loss of its enzymatic activity.