EXTRACTION AND CHARACTERIZATION OF POLYPHENOL OXIDASE IN PAWPAW (ASIMINA TRILOBA) FRUIT CAODI FANG 1 , CHANGZHENG WANG 3 , YOULING L. XIONG 1,2,5 and KIRK W. POMPER 4 1 Graduate Center for Nutritional Sciences 2 Department of Animal and Food Sciences University of Kentucky Lexington, KY 40546 3 Human Nutrition Program 4 Horticultural Research Program Kentucky State University Frankfort, KY 40601 Accepted for Publication November 10, 2006 ABSTRACT Crude polyphenol oxidase (PPO) was extracted from pawpaw (Asimina triloba) fruit pulp, partially purified by gel filtration and electrophoresed for molecular weight (MW) determination. The enzyme activity was assayed by monitoring the absorbance (420 nm) of the PPO extract-catechol mixtures over time. The PPO activity varied with pH and was the greatest at pH 6.5–7.0. The crude enzyme exhibited a maximum activity at 5–20C, but a brief exposure to 40–80C resulted in a rapid decline or complete loss of the enzyme activity. The enzyme kinetics based on the reaction rate in the linear region (0–60 s) showed a V max of 0.1363/s and a K m of 0.3266 M for the crude PPO. The PPO existed as two isoforms with MWs of 28.2 and 38.3 kDa, respectively. PRACTICAL APPLICATIONS Pawpaw fruit is a low-acid, sweet and aromatic fruit grown in North America. With its intense flavor resembling a combination of banana, mango and pineapple, pawpaw fruit is being used in value-added products such as ice creams, yogurts and baked foods. However, pawpaw fruit has a short 5 Corresponding author. TEL: (859) 257-3822; FAX: (859) 257-5318; EMAIL: ylxiong@uky.edu Journal of Food Biochemistry 31 (2007) 603–620. All Rights Reserved. © 2007, The Author(s) Journal compilation © 2007, Blackwell Publishing 603