POLYMERIZATION OF BETA-LACTOGLOBULIN AND BOVINE SERUM-ALBUMIN AT OIL-WATER INTERFACES IN EMULSIONS BY TRANSGLUTAMINASE

Polymerization of beta-lactoglobulin and bovine serum albumin at the o il-water interfaces in n-tetradecane-in-water emulsions induced by the transglutaminase reaction was studied The emulsions were incubated wi th transglutaminase for various times, and adsorbed and unadsorbed pro tein fractions at the oil-water interfaces were analyzed by sodium dod ecyl sulfate-polyacrylamide gel electrophoresis. While only monomers w ere detected in the unadsorbed fractions, polymers were observed in th e adsorbed fractions of the both proteins. The sizes and amounts of th e polymers increased with incubation time. The incubation with transgl utaminase caused much flocculation of the emulsion stabilized by beta- lactoglobulin. An increase in viscosity was also observed with the flo cculation. The flocculation was probably initiated by the formation of epsilon-(gamma-glutamyl)-lysyl isopeptide bonds between beta-lactoglo bulin molecules adsorbed on different oil droplets. In the case of the emulsion stabilized by bovine serum albumin, however the flocculation and the increase in viscosity occurred to only limited extents by the transglutaminase reaction. This suggests that epsilon-(gamma-glutamyl )-lysyl isopeptide bonds induced by the transglutaminase reaction were formed only between neighboring molecules of bovine serum albumin on the same droplet.