Effect of a microbial calcium-independent transglutaminase on functional properties of a partially purified cowpea (Vigna unguiculata) globulin

A partially purified globulin from cowpea seeds was polymerised by calcium- independent microbial transglutaminase. The level of free amino groups in t he globulin decreased with increase in enzyme concentration, suggesting tha t the cross-linking reaction involved participation of the amino residues. At transglutaminase concentrations of 6-18 mu g ml(-1) emulsifying activity decreased with increasing enzyme concentration and degree of cross-linking , while a similar trend was observed for the foaming property at 6-12 mu g ml(-1) transglutaminase concentrations. The resultant emulsions and foams f ormed by the cross-linked proteins were more stable than those formed by th e untreated protein. Sodium dodecyl sulphate polyacrylamide gel electrophor esis showed that of the two major polypeptides, the 55 kDa protein was more susceptible to transglutaminase action than the 50 kDa protein. Scanning e lectron microscopy revealed an amorphous structure for the control protein gel while a more defined and cross-linked gel structure was observed for th e protein treated with transglutaminase. The results suggest that protein p roducts differing in functionalities can be obtained by controlling the deg ree of enzymatic protein cross-linking. (C) 1999 Society of Chemical Indust ry.