Determination of glucosinolates using their alkaline degradation and reaction with ferricyanide

Glucosinolates, a group of naturally occurring thioglucosides, are signific ant factors impairing the nutritional quality of rapeseed and postextractio n rapeseed meal, restricting its use as high-quality protein animal feed. C urrently, the European Community standards and Canola definition are being brought in line recommending cultivation and marketing of rapeseed with a g lucosinolate content below 18 mu mol of total glucosinolates per gram of se eds. Furthermore, some glucosinolates are of increasing interest in Brassic a vegetables due to their proven cancer-preventing activities. A novel appr oach to the analysis of total glucosinolates is reported in this paper base d on their alkaline degradation and subsequent reaction of released 1-thiog lucose with ferricyanide. The reaction was followed spectrophotometrically using sinigrin and glucotropeaolin as model glucosinolates. The applicabili ty of the method was demonstrated using rapeseed extracts after reducing th e interfering effect of phenolics by their adsorption onto polyvinylpolypyr rolidone. Good agreement with official ISO methods was shown.