Nutritional evaluation of kidney beans ( phaseolus vulgaris ): The isolation and partial Characterisation of Toxic Constituents

Comprehensive fractionation studies on the contents of the seeds of two varieties of kidney bean ( Phaseolus vulgaris ) were carried out. The extent of toxicity of the fractions obtained was assessed from the depression of the growth of rats fed on a mixed diet containing 5% casein protein and 5% unfractionated bean proteins or proportional amounts of fractionated materials. The low molecular weight diffusible materials and the structural water‐insoluble carbohydrate‐protein complexes (10 and 73% of the seeds, respectively) were found to have had little deleterious effects on rat growth performance. However, both protein fractions, the albumins (6.3% of the seeds) and the globulins (11% of the seeds), were found to be toxic. Further fractionation with continuous high‐voltage electrophoresis indicated that most of the toxicity of the albumin fraction might be related to the presence of a range of isolectins. A similar, but not identical, isolectin might also be implicated in the toxicity of the globulin fraction. In addition, these results also demonstrated that the three major storage proteins, glycoprotein I and II and the trypsin inhibitors, which altogether made up about three quarters of the total protein content, could have made a small contribution only to the toxicity of kidney beans.