Functional food science represents one of the more controversial areas of food and health because it suggests using food and the component of food in the relation to the treatment or prevention of disease that has been the territory of drug development rather than food consumption. Functional food have become a matter of public concern because of the industry’s rapid global drive to commercialize and market them, often before the supporting science is substantial or even, in the worst case, has barely started.
The winged bean (Psophocarpus tetragonolobus), also known as the kecipir in Indonesia is one of protein source which is in this paper will be explained as functional food. The winged bean, Psophocarpus tetragonolobus, is a tropical legume with high agronomic potential (Boyd, and Hymowitz 1977). It is relatively easy to find winged bean in traditional market in Indonesia. This bean has been called the "one species supermarket" because practically all of the plant is edible. The beans are used as a vegetable, but the other parts (leaves, flowers, and tuberous roots) are also edible. The flowers are often used to color rice and pastries. Each of these parts of the winged bean provides a source of vitamin A, vitamin C, calcium, iron, and other vitamins (Kadam et al.1981). The winged bean can be claimed as functional food because of its antimicrobial agent as natural medicine and its lectin compounds which will be discussed in this paper.
Not withstanding the widespread use of Psophocarpus tetragonolobus in traditional medicine and despite the fact that many plants exhibit significant toxicity, same as enhancement of mutagenecity, carsinogenecity or embryotoxicity. Latha et al. (2007) have studied the toxicity the crude extract Psophocarpus tetragonolobus pods against Artemia salina and sheep erythrocytes, and antimicrobial activities of this extract. According to their study, the extract of Psophocarpus tetragonolobus pods may be useful as an alternative antimicrobial agent as natural medicine for the treatment of many infectious diseases because of its potency.
Lectins, multivalent cell-agglutinating proteins by virtue of their exquisite sugar specificities, have been found in Psophocarpus tetragonolobus. Lectins are sugar-binding proteins which are highly specific for their sugar moieties. They typically play a role in biological recognition phenomena involving cells and proteins. Lectins from legume plants, such as PHA or concanavalin A, have been widely used as model systems to understand the molecular basis of how proteins recognize carbohydrates, because they are relatively easy to obtain and have a wide variety of sugar specificities. The many crystal structures of legume lectins have led to a detailed insight of the atomic interactions between carbohydrates and proteins. The winged bean tropical legume contains two dimeric glycoprotein lectins of almost similar molecular weights (subunit Mr= 29,000) and monosaccharide specificities, but that differ with respect to their isoelectric points and erythrocyte binding properties (Puri and Surolia 1994).
Because of the high degree of specificity displayed by individual lectins in their recognition of glycoconjugates, they are being employed as highly discriminating probes in studies of membranes normal and transformed cells, in blood typing, in the purification and characterization of carbohydrate containing biopolymers, and in studies of lymphocyte mitogenesis (Lis and Sharon 1986). The winged bean contains two lectins (WBA I and II) with almost identical molecular masses and number of subunit but with differing isoelectic points nad hemaggllutinating activities (Kort 1985). Kort (1985) was utilizing lectins of well characterized specificities as competitors for the binding of WBA II to human erythrocytes, suggested that the lectin binds to H and T antigenic determines on the cell surfaces.