Heat-labile growth-inhibiting factors in beans (Phaseolus vulgaris).

A comparative study in vitro was made of enzyme-inhibiting and hemagg1utinin activities, and the effect on rat growth of 5 varieties of kidney beans (Phaseolus vulgaris). Extracts of 2 bean samp1es were active in agg1utinatingrabbit b100d cells and toxic when .fed to growing rats. Diets prepared with these seeds supp1emented with methionine caused weight 10ss and death when fed to rats a10ne or with a supp1ement of 10% enzymatically or acid-digested casein. Hemagg1utinating activity was observed in the feces of rats fed the raw bean diets. The possibility that the hemagg1utinins are at 1east partly responsible for the toxic effects was examined. Three other samples of kidney beans had no significant hemagglutinating or 1ethal effect. Rats fed the raw seed meals supp1emented with methionine did not gain weight but grew well with a similar diet supp1emented with enzymatically digested casein. Supplements of 10% casein, 1% Na glutamate, or 10% acid-digested casein did not improve growth significantly but the latter did when tryptophan was added. Antitrypsin and antiamylase activities were low or absent in some of the seeds and high in others, and did not appear to be directly re1ated to the growth inhibition observed. The low growth-promoting action of the hemagglutinin-free beans might be explained by 10w digestibility and an enzyme-inhibiting activity of the bulk proteins different from that of the trypsin or amylase inhibitors. The existence of a marked inhibitory action on the growth of experimental animals fed diets containing various raw legumes, especially beans or soybeans, has been well-established. Biochemically active factors defined by their in vitro action have been observed and related to the anti-nutritional effect, notably trypsin inhibitors and hemagglutinins or lectins. The extensive literature has been reviewed by Liener (1). The relative importance of these 2 factors and the existence of other ill-defined growth inhibitors is still subject to controversy. Although a number of papers have been published in recent years on this problem, progre ss in this field has been slow. Several factors may be responsible for this situation: The isolation of purified fractions with only one biochemical activity in amounts large enough for toxicological studies is difficult; a purified fraction incorporated into a non-toxic diet may have a different effect from that of a combination of active principIes occurring naturally in the seeds; the raw legumes or fractions used were not always sufficiently defined with respect to the different biochemical activities present; and different legume species and even varieties of one species may vary considerably in respect to different bioJ. NUTRITION, 94: '68. chemical and biological activities, a fact often neglected in this type of investigation. In the present experiments we investigated the different varieties of one species of legumes that are free from or low in one or the other of the biochemically active factors suspected of· being related to toxicity. The growth-promoting or toxic effects of diets prepared with equal amounts of the different ground seeds with known hemagglutinin and enzyme inhibitor content were compared in an attempt to relate these factors and the nutritional properties without the need of fractionation. MATERIAL S AND METHODS The legume seeds were purchased at a local market and finely ground in a hammer millo One part of them was soaked in water for 2 to 3 hours, autoclaved for 30 minutes at 118 o, fan-dried, and then reground. The experimental diets contained, unless stated otherwise, the following ingredients: (in percent) ground legume seed meal, 40; corn oil with 0.2% percomorphum oil, 5; salt mixture USP XVI, 4; DL-methionine, 0.3; and the following vitamins (2) per Received for publication August 28, 1967. 1Present address: Centro Latinoamericano de Enseñanza e Investigación de Bacteriología Alimentaría, Lima, Peru.