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Comparison of fisetin and quercetin oxidation with a cell‐free extract of onion trimmings and peel, plant waste, containing peroxidase enzyme: a further insight into flavonol degradation mechanism
Author(s) -
Osman Ali,
Makris Dimitris P.
Publication year - 2010
Publication title -
international journal of food science and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.831
H-Index - 96
eISSN - 1365-2621
pISSN - 0950-5423
DOI - 10.1111/j.1365-2621.2010.02408.x
Subject(s) - fisetin , protocatechuic acid , quercetin , chemistry , peroxidase , substrate (aquarium) , enzyme , flavonoid , antioxidant , catechol , biochemistry , organic chemistry , biology , ecology
Summary A peroxidase‐active, cell‐free extract prepared from onion solid wastes was studied with regard to its biocatalytic properties, using fisetin (3,3′,4′,7‐tetrahydroxyflavone) as substrate. This particular substrate was selected to investigate specifically the role of the A‐ring of the flavonol skeleton in the oxidisability and cleavage pathway(s), and ascertain whether changes in substitution pattern may affect product formation, compared with quercetin (3,3′,4′,5,7‐pentahydroxyflavone). Oxidation was shown to be optimum at pH values between 5 and 7 and temperatures between 20 and 40 °C. HPLC analyses of a fisetin solution treated with the cell‐free extract revealed the formation of three major products, including 3,4‐dihydroxybenzoic acid (protocatechuic acid), 2,4‐dihydroxybenzoic acid ( β ‐resorcylic acid) and the depside 2‐(3,4‐dihydroxybenzyloxy)‐4‐dihydroxybenzoic acid. The tentative identification of these substances permitted an approach to a putative oxidation pathway, which appeared to have important similarities with that of quercetin.