Toxic Factors in Edible Legumes and Their Elimination

Abstract

Perhaps the best known of the antinutritional factors found in legumes is the trypsin inhibitor which is widely distributed in nature. Despite the considerable amount of research has been conducted on this substance, especially in soy beans, the exact mechanism whereby it inhibits the growth of experimental animals is still not clearly understood. The most recent evidence would seem to implicate pancreatic hypertrophy as one of the main physiologic responses to the trypsin inhibitor. Many legumes also contain substances which agglutinate red blood cells. That they may have nutritional significance is indicated by the fact that purified preparations of these plant hemagglutinins inhibit growth when incorporated into the diets of rats. Their mode of action, however, remains obscure. Other toxic components reported to be present in a wide variety of legumes include goiterogenic factors, cyanogenetic glucosides, saponins and alkaloids. Lathyrism and favism are diseases in man which are associated with the consumption of the specific legumes, Lathyrus sativus and Vicia faba, respectively. Although toxic principles have been isolated from several species of lathyrus which can produce neurotoxic symptoms in animals, the exact etiology of this disease in man is not known. No toxic principle (capable of producing a disease resembling favism in animals) has yet been isolated from Vicia faba. Most of the antinutritional or toxic effects of legumes can be partially or wholly eliminated by proper methods of cooking. This accounts for the fact that heating serves to enhance the nutritive value of many legumes. Since the protein of most leguminous seeds is deficient in methionine, supplementation with this amino acid frequently effects a marked improvement in the biological value of the protein. It is still not clear, however, to what extent the effectiveness of methionine and other dietary supplements might also be due to their ability to counteract the nutritional stress imposed by these toxic components.