中文摘要：

马铃薯在储存和加工过程中易褐变,本实验研究了3种4-卤代苯甲酸（4-氟代苯甲酸、4-氯代苯甲酸、4-溴代苯甲酸）对褐变中的关键酶——多酚氧化酶活性的抑制作用。实验表明,4-氟代苯甲酸、4-氯代苯甲酸、4-溴代苯甲酸对该酶均有明显的抑制作用,测得使该酶活力下降50%所需的抑制剂浓度（IC50）分别为0.635、0.370、0.300mmol/L。抑制动力学实验表明这三种4-卤代苯甲酸对该酶均表现为可逆的非竞争性抑制作用,其抑制常数分别为0.632、0.365、0.303mmol/L。随着卤族元素分子量的增大,对酶的空间位阻增强,导致抑制效率的显著增强。

英文摘要：

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 ICs0, 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（Kr=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-chlombenzoic acid 〉 4-fluorobenzoic acid. This indicated that the inhibitory efficiency on the enzyme is affected by the block of space of the substituted groups.