Inhibitory effects of p-alkylbenzoic acids on the activity of polyphenol oxidase from potato (Solanum tuberosum)

In order to prevent potato from browning during preservation and processing, the effects of p-alkylbenzoic acids (p-propylbenzoic acid, p-butylbenzoic acid, p-pentylbenzoic acid, p-hexylbenzoic acid, p-heptylbenzoic acid, p-octylbenzoic acid) on the activity of potato polyphenol oxidase (PPO) have been studied. The PPO was extracted with PBS (pH 6.8), fractionated with ammonium sulphate, concentrated, and purified with Sephadex G-100 (1.8 × 100 cm) filtration chromatography. The active fractions were pooled and the PPO activity was determined to be 79.83 U/mg. The results showed that p-alkylbenzoic acids could strongly inhibit the activity of potato PPO. The values of IC50 of these six inhibitors were determined to be 0.213, 0.180, 0.152, 0.106, 0.075 and 0.047 mM, respectively. Kinetic analyses showed that p-alkylbenzoic acids used in this experiment were reversible and noncompetitive inhibitors to the enzyme. The inhibitory effects were potentiated with increasing lengths of the hydrocarbon chains, indicating that the inhibitory efficiency on the enzyme was influenced by the steric effect of the substituted groups.