Characterization of tannase-producing bacteria in cowpea (Vigna unguiculata L.Walp)

Bacteria populations isolated from Cowpea were screened on tannic acid agar medium and determined by zones of hydrolysis after 48 h of incubation at 35°C with three bacteria isolates with isolate codes; DVN 5, DVN 8 and DVN 17a, identified as Enterococcus faecalis, Enterococcus sp. and Staphylococcus sp. respectively observed as having the highest zones of hydrolysis and subjected to further screening. Tannase production was carried out via submerged fermentation at 37°C and 120 rpm for 120 h. Tannase activity was measured using the Dinitrosalicyclic method and DVN 5 showed the greatest activity; its enzyme was labeled A1 and was subjected to further enzyme characterization. The optimum condition for tannase activity was determined using a number of parameters such as temperature, pH, effect of substrate concentration, effect of various cations and effect of cation concentration. Optimum conditions were therefore ascertained at a temperature of 60°C, a pH of 9.0, substrate concentration of 0.8 g and a Mg2+ concentration of 1 mM. The Michealis-Menten constant (Km) value for the hydrolysis of tannic acid was approximately 0.0037 mg/ml while the maximum velocity (Vmax) was approximately 9.1408. This study established that tanninolytic bacteria species can be isolated from cowpea and used to produce tannase in appreciable quantities.