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Biochemical studies of cocoa bean polyphenol oxidase
Author(s) -
Lee Pat M,
Lee KongHung,
Ismail Mohd,
Karim Abdul
Publication year - 1991
Publication title -
journal of the science of food and agriculture
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.782
H-Index - 142
eISSN - 1097-0010
pISSN - 0022-5142
DOI - 10.1002/jsfa.2740550210
Subject(s) - catechol , chemistry , polyphenol oxidase , catechol oxidase , substrate (aquarium) , ascorbic acid , enzyme , enzyme assay , laccase , phenols , thiourea , biochemistry , food science , organic chemistry , peroxidase , biology , ecology
Abstract Polyphenol oxidase (EC 1.14.18.1) was isolated and partially purified from cocoa beans. The properties of the enzyme were studied. The Michaelis constant K m for catechol was 1 × 10 −2 M . The pH optimum of polyphenol oxidase activity assayed with catechol as substrate occurred at pH 6.8 and was characterised by a relatively high thermal stability, 50% of its activity was lost after heating for 40, 25 and 5 min at 60, 69 and 80°C respectively. The optimum temperature for the enzyme activity with catechol as substrate was around 45°C. The enzyme was reactive towards 3‐(3,4‐dihydroxy phenyl)‐ DL ‐alanine, 3‐hydroxytyramine hydrochloride and 4‐methyl catechol but showed no activity towards tyrosine, p ‐cresol, and 4‐hydroxy‐phenol. A rapid deactivation of the enzyme was observed when catechol of concentration > 40 mM was used as substrate. The enzyme activity was inhibited by ascorbic acid, L ‐cysteine, sodium bisulphite and thiourea.