World Journal of Biochemistry and Molecular Biology 2018; 3(1): 22-30 http://www.aascit.org/journal/wjbmb Partial Purification and Characterization of Polyphenol Oxidase from Water Yam (Dioscorea alata) Belonwu Chijioke Mmuoasinam 1 , Philippa Chinyere Ojimelukwe 2, * , Evelyn Njideka Bede 3 1 Department of Food Science and Technology, Imo State Polytechnic Umuagwo, Ohaji, Nigeria 2 Department of Food Science and Technology, Michael Okpara University of Agriculture, Umudike, Nigeria 3 Department of Food Science and Technology, Federal University of Technology, Owerri, Nigeria Email address * Corresponding author Citation Belonwu Chijioke Mmuoasinam, Philippa Chinyere, Ojimelukwe, Evelyn Njideka Bede. Partial Purification and Characterization of Polyphenol Oxidase from Water Yam (Dioscorea alata). World Journal of Biochemistry and Molecular Biology. Vol. 3, No. 1, 2018, pp. 22-30. Received: February 25, 2018; Accepted: March 21, 2018; Published: May 10, 2018 Abstract: The aim of this research was to evaluate enzymic browning of Discorea alata and determine methods of preventing and controlling the browning reaction. Polyphenol oxidase (PPO) was extracted from water yam and partially purified by acetone precipitation and dialysis. Optimal pH activity, substrate specificity and inhibition studies of this enzyme was carried out. The result revealed a 9.9 fold increase in activity after dialysis of acetone enzyme precipitate. Substrate specificity of water yam PPO showed activity for diphenolic compounds- catechol, methylcatechol and L-DOPA while no activity was observed in the presence of monophenolic compound, p-cresol. Optimal pH activity of this enzyme was observed at pH 6.8. Tyrosine, phenylthiourea and hydroquinone inhibited water yam PPO competitively in the presence of catechol while ascorbic acid and 2-mercaptoethanol completely inhibited this enzyme at concentrations used. Activation of catechol oxidation by the water yam PPO was observed in the presence of pyrogallol and garlic acid. The data obtained from this inhibition study may be used to predict prevention of browning in yam tuber using chemical inhibitors. Keywords: Enzymic Browning, Discorea alata, Inhibitors, Polyphenol Oxidase 1. Introduction Browning phenomenon is commonly observed in foods during processing and preservation. Enzymatic browning, a type of browning in foods, is known to be caused predominantly by a group of enzymes, polyphenol oxidases (PPOs), which are naturally distributed from bacteria to mammals. They catalyse the oxidation of phenolics to quinones with eventual production of brown pigments in bruised tissues [1]. Polyphenol oxidase has been isolated from higher plants such as sour cherry [2], lemon balm [3], banana [4], Anna apple [5], white cherry fruit [6], taro [7], mushroom [8], soursop [9] and Chinese water chestnut [10]. In addition to pigment formation in plants, polyphenol oxidase is implicated in oxygen scavenging and defence activities against plant pathogens and predatory insects [11]. Water yam is widely distributed and is being cultivated in the tropical and subtropical parts of Africa, America, Asia and Caribbean [12]. Yams, generally, are considered important food staples in many African countries, comprising Cote d’ Ivore, Ghana, Togo, Burkina Faso and Nigeria [12] [13]. Further to food uses, some yams are used as medicines to prevent diarrhoea and diabetes [14] [15] while few species are popular medicines for indigestion and intestinal colic, soothing of diverticulitis, relieve of dysmenorrhoea, as well as allaying uterine and ovarian pain [15] [16]. In spite of these numerous benefits associated with yam, it’s processing, storage and distribution is highly affected by the activities of polyphenol oxidase resulting in browning of stored fresh tubers and products made from it. Hence, this study was aimed at extraction and