Tannins and Saponins in Two Tropical Legumes and Measurement of their Biological Activity

Aims: Raw tropical legumes have abundant amounts of tannins and saponins which are usually eliminated with high temperature once they are cooked. These biomolecules may represent new alternatives, to allopathic medicine, in order to prevent the accumulation of free radicals affecting the cells, or to prevent thrombosis in the blood stream respectively. Therefore the aim of this study was to evaluate the antioxidant and antithrombotic activity attributed to tannins and saponins in whole seeds flour (WSF) and fractions resulting in three types of components: endosperm (flour without hulls –Fw/oH-), protein concentrate (PC) and hulls, of two types of tropical legumes Vigna unguiculata (Cowpea) and Mucuna pruriens (Velvet bean). Analysis of nutritional value and also tannins and saponins content was carried out. Finally, antioxidant and antithrombotic activity was also estimated.
Place and Duration of Study: Experiments were carried out in the laboratory of Food Science of the Faculty of Chemical Engineering of the Autonomous University of Yucatán, located in Mérida, Yucatán. México, during 2011-2012.
Study Design: Variables were analyzed with descriptive statistics and using the method of Generalized Linear Model to detect the effect of the type of legume, type of component and their interaction.
Methodology: Analysis of nutritional value and also tannins and saponins content was carried out. Finally, antioxidant (5093 Trolox equivalent units, TEAC) and antithrombotic activity (measurement of the capacity to inhibit the aggregation of blood platelets) was also estimated (n =3).
Results: Type of legume did not affect protein content (p>.05), but there were differences in the content of moisture, fat, ash and carbohydrate (p<.05); different seed fractions exhibited different nutritional profile. Tannin content was greater in M. pruriens (0.63%) compared to V. unguiculata (0.38%) (p<.01); among the components tested, a higher concentration was detected in WSF (1%)(p<.01). The greatest antioxidant activity was observed in V. unguiculata (p<.01) whereas in the fractions, the highest concentration was found in the hulls (5937 TEAC) (p<.01). These values are considered high. Saponin content was higher in V. unguiculata (25.8 mg / g) (p<.01); as far as the components tested, the hulls had a higher content (22.7 mg / g) (p<.01). Antithrombotic activity was similar in both legumes and as far as the components is concern, the most abundant amount was found in the Fw/oH. In all cases, values were found to be low.
Conclusion: V. unguiculata hulls showed high antioxidant activities, which were inversely related to tannin content. Saponin content apparently was not associated with antithrombotic activity since it was found to be low in both legumes.