Abstract

• Extraction and purification of polyphenol oxidase from cabbage (Brassica oleracea L.) were performed by ammonium sulphate precipitation (35-85 %) and gel filtration chromatography on Sephadex G-100. Polyphenol oxidase activity was determined using catechol as a substrate at 420 nm. The protein content was also determined by the Biuret method, using Bovine Serum Albumin (BSA) at 550 nm. The optimum pH and temperature of both crude and partially purified polyphenol oxidase enzymes were found to be 7.0 and 40 °C, respectively. The activation energy of the crude polyphenol oxidase-catalyzed reaction was 9.33 kcal mol-1 and that of partially purified enzyme was 6.31 kcal mol-1. The Km (0.052 M) and Vmax (3.03 ×10-5 M min-1) of partially purified polyphenol oxidase were determined by using the Lineweaver-Burk plot. The reaction order (n) of the polyphenol oxidase-catalyzed reaction was calculated by using the linear regression method and it was found to be first order for both crude and partially purified polyphenol oxidase. The crude polyphenol oxidase responded the highest antimicrobial activity against the eight microorganisms tested by the agar well diffusion method.