Enzymatic Characteristics and Inhibition Mechanism of PPO from Boletus edulis
To investigate enzymatic characteristics of PPO,PPO from Boletus edulis was isolated and purified.Based on this study,the thermal inactivation kinetics and inhibition mechanism of PPO were analyzed using kinetic models and Lineweaver-Burk plot methods.The results showed that the enzy-matic reaction product of PPO from Boletus edulis had the maximum absorption wavelength at 407 nm,PPO and catechol had the strongest affinity,and the kinetic parameters of the enzymatic reaction were Km=9.41 mmol/L,Vmax=196.08 U/min.The optimal substrate of PPO was 50 mmol/L cate-chol,the optimum pH was 6.8,the optimal reaction temperature and time were 45 ℃ and 7 min,re-spectively.The PPO enzyme inactivation was fastest at 90 ℃,and the kinetic parameters were k=2.504 5 min-1,D=0.942 0 min,T1/2=0.276 8 min.The activation energy(Ea)for PPO inactiva-tion between 70 ℃ to 90 ℃ was 130.283 kJ/mol.Sodium metabisulfite showed noncompetitive inhibi-tion,while ascorbic acid and L-cysteine showed competitive inhibition.PPO activity can be effectively inhibited by heat treatment and the addition of inhibitors.These findings provide a reference for the quality control of Boletus edulis during postharvest storage and processing.
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