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Purification and Structural Characterization of a Polyphenol Oxidase from Field Bean (Dolichos lablab)

Paul, Beena (2000) Purification and Structural Characterization of a Polyphenol Oxidase from Field Bean (Dolichos lablab). PhD thesis, University of Mysore.


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Polyphenol oxidase (PPO) is a copper-containing enzyme widely distributed in nature, which catalyzes the orthohydroxylation of monophenols and the oxidation of o-diphenols. Browning of fruits and vegetables is initiated by the enzymatic oxidation of phenolic compounds by PPO, and is reported to be one of the main causes of quality loss during post-harvest handling, processing and storage (Mathew and Parpia, 1971). Browning usually imparts a change in color, appearance and organoleptic properties, which are considered detrimental to the food quality. Hence, prevention of PPO activity in fruits and vegetables has enormous economic and quality benefits. However, PPO is sometimes important for the beneficial coloration of some foods such as prune, cocoa, raisin and black tea. For many years the food industry world over used sulfites to prevent browning effectively and economically. However, because of the adverse health effects imparted by the chemical inhibitors and increased awareness in life styles related to food and health,there is an increased demand for more natural foods and fewer, safer added chemicals in processed foods. Hence alternate methods to prevent browning have been investigated. Through an understanding of the structural characteristics, mechanism of action of PPO and chemistry of enzymatic browning, targeted prevention methods can be developed. The purification of PPO from higher plants is hampered by the occurrence of multiple forms and pigment contamination. Although the first PPO, a mushroom tyrosinase was discovered more than a century and half ago, the first three-dimensional structure of a plant PPO became available only in 1998. Pleminary investigations in laboratory, earlier during the structural characterization of a lectin from the field bean seeds (Gowda et al., 1994) revealed the presence of a single PPO in crude extracts. The single form of PPO in field bean seeds renders it ideal for primary structure determination and three-dimensional structure analysis, which in plant PPOs has been hindered by its multiplicity. As a primary step to understand the structure, regulation and function of seed PPO, the isolation and characterization of a PPO from field bean seeds was carried out. In the last four and a half years (May 1996 - December 2000) of this investigation at CFTRI, the single form of PPO from field bean seeds has been purified and the kinetic and molecular properties were explored. In addition, due to the demand and need for natural compounds which inhibit PPO, a high molecular weight inhibitor of PPO was isolated from raw sapota extract and characterized.

Item Type: Thesis (PhD)
Uncontrolled Keywords: Polyphenol oxidase field bean dolichos lablab purification characterization
Subjects: 600 Technology > 08 Food technology > 22 Legumes-Pulses
500 Natural Sciences and Mathematics > 04 Chemistry and Allied Sciences > 16 Enzyme Chemistry
Divisions: Protein Chemistry and Technology
Depositing User: Food Sci. & Technol. Information Services
Date Deposited: 06 Jun 2008 05:02
Last Modified: 28 Dec 2011 09:34
URI: http://ir.cftri.com/id/eprint/1740

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