Determination of glucosinolates using their alkaline degradation and reaction with ferricyanide

Glucosinolates, a group of naturally occurring thioglucosides, are significant factors impairing the nutritional quality of rapeseed and postextraction rapeseed meal, restricting its use as high-quality protein animal feed. Currently, the European Community standards and Canola definition are being brought in line recommending cultivation and marketing of rapeseed with a glucosinolate content below 18 mu mol of total glucosinolates per gram of seeds. Furthermore, some glucosinolates are of increasing interest in Brassica vegetables due to their proven cancer-preventing activities. A novel approach to the analysis of total glucosinolates is reported in this paper based on their alkaline degradation and subsequent reaction of released 1-thioglucose with ferricyanide. The reaction was followed spectrophotometrically using sinigrin and glucotropeaolin as model glucosinolates. The applicability of the method was demonstrated using rapeseed extracts after reducing the interfering effect of phenolics by their adsorption onto polyvinylpolypyrrolidone. Good agreement with official ISO methods was shown.