Study On The Properties Of Potato Polyphenol Oxidase And The Inhibition Mechanism Of Its Inhibitors

Polyphenol oxidase (EC 1.14.18.1) is widely distributed in microorganisms, animals and plants.It is a copper-containing enzyme which has complex constructure. Polyphenol oxidase (PPO) acts as an important role during the process of enzymetic browning in fruit and vegetable,for the reason that it can catalyze the melanin Synthesis. The studies of the enzymetic characteristics, catalytic mechanism and inhibition mechanism of PPO were very important in anti-browning research field.In this paper, we purified the PPO from potato and studied some physical and chemical properties of this enzyme.Optimum temperature and optimum pH were determined to be 30℃and 6.0 respectively. Km was determined to be 7.24 mmol/L at 30℃and pH 6.8. The enzyme activity was stable at the pH ranging from 5.15～.75 and under 50℃.The effects of metal ions on the PPO for the oxidation of L-DOPA were studied. The results showed that Li⁺, K⁺, Ba²⁺ and Mg²⁺ had no effect on the PPO activity, Al³⁺, Fe³⁺, Cd²⁺, Mg²⁺, Co²⁺, Pb²⁺, Mn²⁺ and Zn²⁺ activated the activity of PPO. Cu²⁺ could inhibit the activity of PPO.The effects of some organic solvents, including alcohol compounds, aldehyde compounds, acetone, dimethylsulfoxide and dioxane, on the potato PPO for the oxidation of L-DOPA were studied. The IC50 values and the inhibitory mechanisms were determined and compared.Benzoic acid,benzladehyde and 18 benzoic acid family compounds were studied in order to screen the inhibitor of PPO. The results showed that all of the tested compounds had effects on potato PPO. The reactions of these compounds were reversible with remaining enzyme activity.The structures of these compounds were the foundation of inhibit ability and inhibit mechanism.The mechanisms and effects of sodium bisulfite and sodium metabisulfite on the potato PPO were studied.The results showed that they have some unreversible inhibit on the enzyme,and they could increase the lag time of potato PPO.On the basis of the study that were carried out in above part , We chosen sodium bisulfite, sodium metabisulfite and calcium chloride as inhibitors for the anti-browning research on fresh-cut potato slices. We studied the effects of immersing time on the...