From soybeans to lectins: a trail of research revisited

Bioactive peptides in cereals and legumes: agronomical, biochemical and clinical aspects

Cereals and legumes are key components of a healthy and balanced diet. Accordingly, many national nutritional guidelines emphasize their health promoting properties by placing them at the base of nutritional food pyramids. This concept is further validated by the observed correlation between a lower risk and occurrence of chronic diseases and the adherence to dietary patterns, like the Mediterranean diet, in which cereal grains, legumes and derived products represent a staple food. In the search for a dietary approach to control/prevent chronic degenerative diseases, protein derived bioactive peptides may represent one such source of health-enhancing components. These peptides may already be present in foods as natural components or may derive from hydrolysis by chemical or enzymatic treatments (digestion, hydrolysis or fermentation). Many reports are present in the literature regarding the bioactivity of peptides in vitro and a wide range of activities has been described, including antimicrobial properties, blood pressure-lowering (ACE inhibitory) effects, cholesterol-lowering ability, antithrombotic and antioxidant activities, enhancement of mineral absorption/bioavailability, cyto- or immunomodulatory effects, and opioid-like activities. However it is difficult to translate these observed effects to human. In fact, the active peptide may be degraded during digestion, or may not be absorbed or reach the target tissues at a concentration necessary to exert its function. This review will focus on bioactive peptides identified in cereals and legumes, from an agronomical and biochemical point of view, including considerations about requirements for the design of appropriate clinical trials necessary for the assessment of their nutraceutical effect in vivo.

Plant as a plenteous reserve of lectin

Lectins are clusters of glycoproteins of nonimmune foundation that combine specifically and reversibly to carbohydrates, mainly the sugar moiety of glycoconjugates, resulting in cell agglutination and precipitation of glycoconjugates. They are universally distributed in nature, being established in plants, fungi, viruses, bacteria, crustacea, insects, and animals, but leguminacae plants are rich source of lectins. The present review reveals the structure, biological properties, and application of plant lectins.

Nutritional and health benefits of soy proteins

Soy protein is a major component of the diet of food-producing animals and is increasingly important in the human diet. However, soy protein is not an ideal protein because it is deficient in the essential amino acid methionine. Methionine supplementation benefits soy infant formulas, but apparently not food intended for adults with an adequate nitrogen intake. Soy protein content of another essential amino acid, lysine, although higher than that of wheat proteins, is still lower than that of the milk protein casein. Adverse nutritional and other effects following consumption of raw soybean meal have been attributed to the presence of endogenous inhibitors of digestive enzymes and lectins and to poor digestibility. To improve the nutritional quality of soy foods, inhibitors and lectins are generally inactivated by heat treatment or eliminated by fractionation during food processing. Although lectins are heat-labile, the inhibitors are more heat-stable than the lectins. Most commercially heated meals retain up to 20% of the Bowman-Birk (BBI) inhibitor of chymotrypsin and trypsin and the Kunitz inhibitor of trypsin (KTI). To enhance the value of soybeans in human nutrition and health, a better understanding is needed of the factors that impact the nutrition and health-promoting aspects of soy proteins. This paper discusses the composition in relation to properties of soy proteins. Also described are possible beneficial and adverse effects of soy-containing diets. The former include soy-induced lowering of cholesterol, anticarcinogenic effects of BBI, and protective effects against obesity, diabetes, irritants of the digestive tract, bone, and kidney diseases, whereas the latter include poor digestibility and allergy to soy proteins. Approaches to reduce the concentration of soybean inhibitors by rearrangement of protein disulfide bonds, immunoassays of inhibitors in processed soy foods and soybean germplasm, the roles of phytoestrogenic isoflavones and lectins, and research needs in all of these areas are also discussed. This integrated overview of the widely scattered literature emphasizes general concepts based on our own studies as well as recent studies by others. It is intended to stimulate interest in further research to optimize beneficial effects of soy proteins. The payoff will be healthier humans and improved animal feeds.

Biological response of rats fed with tofu treated with high hydrostatic pressure

Emerging technologies for food preservation have arisen in recent years, such as high-pressure (HP) hydrostatic treatment, and the biological response for this kind of food preservation is not well-known. Forty female rats (six weeks old) were used in the experiment to evaluate the biological effects of HP treatment of tofu. The animals were divided into groups that were fed with tofu (untreated), tofu treated with HP, and conventional food (as control) for 28 days. The glucose level, mineral content (calcium, potassium, zinc, and magnesium), shinbone maximum shear force, weight of the body, and weight of organs (heart, liver, spleen, and kidneys) were analyzed. The biological response for the rats was that significant differences were found in the calcium amount determined on the serum of the rats fed with untreated tofu and those fed with tofu treated with HP, and the calcium amount was lower on the rats fed with tofu treated with HP. Also, there were significant differences in the weight of the liver, and it was lower in the rats fed with tofu treated with HP. It was quite remarkable how the weight of the body and organs were smaller in the rats fed with tofu in comparison to the weight of the control rats. In the other components assayed no significant differences were found. HP produces a potential effect on tofu as it is observed in the rats response to the tofu treated with HP.

Implications of antinutritional components in soybean foods

There are a number of components present in soybeans that exert a negative impact on the nutritional quality of the protein. Among those factors that are destroyed by heat treatment are the protease inhibitors and lectins. Protease inhibitors exert their antinutritional effect by causing pancreatic hypertrophy/hyperplasia, which ultimately results in an inhibition of growth. The lectin, by virtue of its ability to bind to glycoprotein receptors on the epithelial cells lining the intestinal mucosa, inhibits growth by interfering with the absorption of nutrients. Of lesser significance are the antinutritional effects produced by relatively heat stable factors, such as goitrogens, tannins, phytoestrogens, flatus-producing oligosaccharides, phytate, and saponins. Other diverse but ill-defined factors appear to increase the requirements for vitamins A, B12, D, and E. The processing of soybeans under severe alkaline conditions leads to the formation of lysinoalanine, which has been shown to damage the kidneys of rats. This is not generally true, however, for edible soy protein that has been produced under milder alkaline conditions. Also meriting consideration is the allergenic response that may sometimes occur in humans, as well as calves and piglets, on dietary exposure to soybeans.