BIOSENSING OF RAPESEED GLUCOSINOLATES USING AMPEROMETRIC ENZYME ELECTRODES BASED ON MEMBRANE-BOUND GLUCOSE-OXIDASE OR TYROSINASE

Sinigrin, the beta-D-thioglucoside of the cruciferous plant species wa s hydrolyzed for 15 min at pH 7 and 30 degrees C by the enzyme myrosin ase to liberate glucose and mustard oil allylisothiocyanate as aglucon e. A Clark-type pO(2) sensor overlaid with a glucose oxidase + catalas e membrane served for the glucose measurements, whereas the isothiocya nate component was measured (after conversion to allylthiourea) from t he inhibition degree of a tyrosinase membrane/pO(2) sensor. The total amounts of glucosinolates found with the glucose probe in six assorted samples of rapeseed meal and evaluated in sinigrin equivalents (13.6- 147 mu mol/g) agreed with those obtained using gas chromatography as t he reference. Poor agreement (results: 111.4-112.3%) was achieved when a different method of fat removal was used 7 prior to electroanalysis . The amounts of progoitrin (not convertible to thiourea) estimated in directly from the difference of both the glucose and the aglucone bios ensor analyses were found to be in the range 6.2-103 mu mol/g (44.3-83 .8% of the total glucosinolates).