Analytical Sciences

Application of Crude Extract of Kohlrabi (Brassica oleracea gongylodes) as a Rich Source of Peroxidase in the Spectrofluorometric Determination of Hydrogen Peroxide in Honey Samples

Jamshid L. MANZOORI, Mohammad AMJADI, and Maghsood OROOJI

Department of Analytical Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz, Iran

Crude extract of kohlrabi (Brassica oleracea gongylodes) was prepared by a simple procedure and its enzymatic activity and total protein concentration were determined. It was found that this crude extract is a rich source of peroxidase (POx) and has high specific activity. Cross-linked polyvinylpyrrolidone was used as a stabilizer in the preparation of the crude extract. The POx activity of kohlrabi crude extract did not vary for at least 2 months when deoxygenated and stored at 4°C. This extract was applied for the spectrofluorometric determination of hydrogen peroxide using homovanillic acid as a fluorogenic substrate. POx catalyzes the hydrogen peroxide oxidation of homovanillic acid to produce a dimer which shows strong fluorescence at 420 nm with excitation at 312 nm. In the optimum conditions, the calibration graph for hydrogen peroxide was linear up to 190 ng mL^-1, with a detection limit of 4.4 ng mL^-1. The relative standard deviation (RSD) was 1.48% for 50 ng mL^-1 hydrogen peroxide. The proposed method was successfully applied to the determination of hydrogen peroxide in honey. The concentration-time profile of H₂O₂ produced upon dilution of honey was studied and H₂O₂ contents of some different honeys from various areas of Iran were determined.

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