Vanillic Acid: An Antioxidant used in Preventing Browning Process in Pear (Pyruscommunisl.) Juice

Abstract

Abstract:In this study, Polyphenol Oxidase (PPO) was partially purified from pear fruit pulp which was organically grown in Mosul city of Iraq. The crude enzyme-specific activity was (222.42) Unit/mg protein. After applying precipitation by ammonium sulfate and dialysis, the specific activities have been improved to be (211.66) and (549.60) Unit/mg protein, and the purification folds were (0.95) and (2.47) respectively. After ion-exchange chromatography using CM - Cellulose, the final result revealed one peak of PPO with a specific activity of (11306.1) Unit/mg protein and purification fold of (50.83). Characterization of the partially purified enzyme showed that optimum pH and temperature were 7.5 and 35°C respectively. Polyphenol Oxidase activity and browning intensity in pear juice were inhibited by adding different concentrations of antioxidant compound, vanillic acid. The maximum inhibition percentage of the enzyme was 71.1% and the maximum inhibitory effect of browning intensity was 30.9 %. The inhibition mode of purified PPO was competitive by using 3.3 mMvanillic acid. Michaelis-Menton (Km) value increased from (1.43) to (3.33) mM, with unchanging in Maximum velocity (Vmax)value (123.45) Unit/ml.min. The inhibition constant (Ki) value was 1.846 mM. The results of untreated pear juice indicated decreasing in phenolic compound contents, reducing sugar and free amino group but, increasing in intermediate compounds, browning intensity, and reducing power. After treating with (3.3mM) vanillic acid, decreasing of intermediate compounds, browning intensity, and increasing in reducing power were revealed with comparing to control. Contrariwise, the addition of vanillic acid to pear juice obtained increasing in reducing sugar, free amino acid, and phenolic contents compared to control.