Asian J. Research Chem. 4(11): Nov., 2011 1780 ISSN 0974-4169 www.ajrconline.org RESEARCH ARTICLE Bioactive Molecule of Onion Leaves Act as Inhibitor of PPO. A. S. Goswami-Giri* and Neha A. Sawant B.N. Bandodkar College of Science, Thane-400 601. *Corresponding Author E-mail: anitagoswami@yahoo.com ABSTRACT: Bioactive molecules of onion leaves exhibited potent anti polyphenol oxidase (PPO) activity; which was purified on silica gel by using solvents. Purification profile procured 3 and 2 active butanol and methanol fractions respectively. Reticence of PPO activity was observed within range of 12 to 14 min when it was treated with active fractions. Characterization of it was conceded by physical constant, UV, IR and TLC. It reputes that, active hydroxyl group attached to the ring structures of PPO, which quench free radical by donating hydrogen in the active hydroxyl group of PPO, confirming inhibition of pigmentation reaction in vitro. Bioactive molecules from onion leaves exhibited various types of inhibition against oxidation of L-DOPA and L-tyrosine and it was compared with classical inhibitors of PPO. Significance of bioactive molecules is to explore for drugs designing, understanding of ligand–receptor interactions, environmental problems and it is simple alternative for the inhibition of PPO. KEYWORDS: Onion leaves; quercetin; oxazolone; flavanoid; cinnamic acid; inhibition. INTRODUCTION: Onion and onion leaves is essential ingredient of vegetarian and non-vegetarian diets having medicinal and nutritive value. Though onion is useful, onion leaves turn black when cut, due to oxidation of 3, 4-dihydroxyphenylalanine (dopa) to pigmented products. This reaction is catalyzed by group of enzymes; polyphenol oxidase (PPO). Pigmentation is often an undesirable reaction, which is responsible for unpleasant sensory qualities, significant loss in nutritional qualities and market value of fruits/vegetables. The prevention of this reaction has always been a challenge to food scientist 1 . Discrimination of this reaction is responsible for various types of diseases and disorders viz Parkinsonia 2 , albinism, melanoma, psychological effect- schizophrenia 3,4 , gastrointestinal side effects and melanin- based bias in human societies. In India, Maharashtra is the major place where fruits and vegetable are cultivated on a large scale but in peak season if transport facilities become unavailable, fruits and vegetable being perishable, leads to economic loss to the farmers. Consequently change in color is a major problem. Many inhibitors are often used to prevent the pigmentation, which are toxic to human beings. Received on 16.09.2011 Modified on 03.10.2011 Accepted on 18.10.2011 © AJRC All right reserved Asian J. Research Chem. 4(11): Nov., 2011; Page 1780-1783 Therefore searching for nontoxic inhibitors having broad application for these activities is important in developing a rational chemotherapy of pigmentation. In the present paper, the biologically active compounds from onion leaves extracted by using organic solvent were bioassay for inhibitory effect. Bioactive conformation of drugs is one of the key points for understanding the ligand–receptor interactions 5 . Therefore, the Onion leaves organic extract was purified on silica gel. Fractions were characterized by physical constant, TLC, UV and IR spectra. MATERIALS AND METHODS: Materials: L-dopa, l-tyrosine, sodium phosphate (mono and dibasic), ammonium sulfate, citron X-100, EDTA, ascorbic acid were obtained from E. Merck (India). Sephadex G-25 from pharmacia, silica gel ammonium hydroxide, di-ethylether , chloroform, acetone from Loba Chemicals, butanol from SRL. Other chemicals used were of analytical pure grade. Methanol was obtained locally and was distilled prior to use. Source: Fresh onion leaves were obtained directly from the fields, were washed and then stored at 4°C in a refrigerator for about 24 hrs. PPO extraction from onion leaves by solvent and salt method: Fresh onion leaves (300 g) were homogenized with 150 ml of ice-cold acetone, water with Citron X-100 (80:19:1,