The Estimation of Vicine in Fababeans by an Ultraviolet Spectrophotometric Method

Abstract

Advantage was taken of the strong ultraviolet absorption of vicine (the jS—D—glucoside of divicine) at 273.5 nm (e = 16.3 × 103) to estimate the vicine content of protein—free extracts of fababeans and fababean fractions. Recoveries of added vicine were virtually complete. Chromatography of a protein-free bean extract on a cation-exchange resin revealed two ultraviolet—absorbing constituents, apparently convicine (the analogous glucoside of isouramil) and vicine, in the ratio 1:2. Thus, the ultraviolet method estimates convicine plus vicine, or "total vicine." Dialysis and gel—exclusion chromatography of bean extracts indicated that 5–15%of the ultraviolet–absorbing material was not free vicine or convicine. The Higazi—Read colorimetric method for vicine (J. Agr. Food Chem., 1974, 22: 570—571) gave consistently lower results and reasons for this are discussed. Fresh and dried fababeans were rich in total vicine (up to 1%dry weight) and an isolated protein fraction contained 2%. The vicine was loosely bound, as it could be almost completely removed by dialysis or by precipitation of the protein at pH 5. The ultraviolet method is rapid and simple and should be useful for estimating total vicine in cul—tivars and in fababean products prepared for human consumption. The high concentration of total vicine might be a health hazard to susceptible individuals