Plant proteins: food applications and health benefits

The term plant proteins refers mainly to grain legume proteins, since these are the most efficient protein sources among vegetables. The protein content of most legumes (pea, common bean, lentil, chickpea, faba bean etc) is around 22-25%, whereas the content of soybean and lupin may reach 35-42% depending on the variety and the environmental and agricultural conditions. Besides proteins, other important nutritional components in legumes are resistant starch, soluble fibers, alpha-galactosides, unsaturated fatty acids (including alpha-linolenic acid) and antioxidant polyphenols, as well as macro and micro-elements and vitamins. Several populations in developing countries base their protein intake mostly on legumes: this is particularly true for women and children. In industrialized countries, the interest for legume protein is also related to their specific biological activity. In fact the outcomes of numerous clinical studies conducted in Europe and the US have demonstrated that consuming soy protein in place of animal proteins has positive effects on the levels of total and LDL cholesterol. In 1999 the U.S. Food and Drug Administration has approved the health claim on soy foods for the prevention of cardiovascular disease. At present, a similar health claim is pending in the European Union. Detailed studies have shown that the proteins have a predominant role in the cholesterol-lowering activity of soy. Since most legume proteins have considerable sequence homology, several groups, including ours, have undertaken studies on these vegetables. The most investigated are bean (a term indicating some species of the genera Phaseolus and Vigna), pea, faba bean, chickpea and lupin. Numerous experimental studies in different animal models and a few clinical studies are available, which have indicated interesting pharmacological activities, against hypercholesterolemia, hypertension and hyperglycemia. Our attention was mainly focused on lupin whose composition is very similar to soy (high protein content, reduced presence of starch, relatively high concentrations of alpha-linolenic acid). Experimental studies in a rat model of hypercholesterolemia and in a rabbit model of the atherosclerotic plaque, and a double-blind clinical study on moderately hypercholesterolemic patients have shown very promising activities. A clinical study conducted in Australia has shown, instead, a potential hypotensive activity.