Soybean lectin toxicity

Legume seeds contain a number of antinutritive components, mainly lectin and trypsin inhibitors. The efficiency of the nutritional utilization of diets containing soybean is well below that expected on the basis of chemical composition [196]. In order to reduce the extent of this constraint, at present, all soy products go through expensive heat treatment or other processing procedures that can lead to losses of essential amino acids and to the production of toxic by-products. It is hoped that an effective strategy will help improve the nutritional value of soy proteins [197,198]. 

Lectins are of widespread occurrence in legumes (e.g. soybeans, lentils, kidney beans, jack beans). They are potentially toxic as they can impair tissue functions, but the body can usually replace any damaged cells faster than they are destroyed (Johns 1990). Lectins are responsible for toxicity in the notorious garden plant rosary pea—Abrus precatorius. Lectins in foods are readily destroyed by processing and cooking. 

Animal tests have demonstrated that their toxicity often does not parallel hemagglutination activity. Thus, lectins from soybeans and garden beans are toxic, but not those from peas and lentils. These and other observations suggest that it is not the hemagglutination activity but other activities of lectins which are responsible for their toxicity. One toxic effect originates in the, at least partial. 

After cooking or dry heating, the activities of legume lectins and the associated toxic effects are destroyed. After heating to 100 °C for 10 minutes, e. g., soybeans were free of lectin activity. However, the lectins in some legumes are much more stable. 

Non-toxic lectins are lectins of garlic, onions, leeks, tomatoes and amaranth. Of the common lectins, those of peanuts, lentils, peas, common beans and soya beans are slightly toxic, wheat lectins are moderately toxic, and lectins of some beans (such as Jack beans) are highly toxic, while castor seed lectins are lethal (Table 10.21). Some lectins (such as lectins of garlic) have prebiotic effects and inhibit undesirable intestinal microflora Escherichia coli). Often, lectins are not the only toxic substances of the plant material. For example, lectins of soybean seeds participate in their antinutritional and toxic effects at a level of about 25%, but trypsin inhibitors are about 40% and the rest is covered by saponins and other substances. 

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