Abstract: In order to prevent potato from generating brownness during preservation and processing,the effects of 4-halobenzoic acids(4-fluorobenzoic acid,4-chlorobenzoic acid,4-bromobenzoic acid) on the inhibitory effects on the activity of potato polyphenol oxidase(PPO),the key enzyme to browning,have been studied.The results showed that 4-halobenzoic acids can strongly inhibit the activity of potato PPO to lose 50%,the values of IC50,the concentrations of these three inhibitors which lead the activity of potato PPO are determined to be 0.635,0.370 and 0.300 mmol/L,respectively.Kinetic analyses showed that the inhibition mechanism of all three 4-halobenzoic acids are reversible and belong to be noncompetitive inhibition,with the inhibition constants(KI=KIS)determined as:0.632,0.365 and 0.303 mmol/L,respectively.For these three inhibitors,the inhibition potency is in the following order:4-bromobenzoic acid > 4-chlorobenzoic acid > 4-fluorobenzoic acid.This indicated that the inhibitory efficiency on the enzyme is affected by the block of space of the substituted groups.

Key words: potato, polyphenol oxidase, 4-halobenzoic acids, inhibitory effect, kinetics