Role of ovomucoid in the gelation of a [beta]-lactoglobulin-ovomucoid mixture

The effect of ovomucoid on gelation of [beta]-lactoglobulin--as induced by heating and subsequent cooling--was investigated using a mixture of 5 % (w/v) ovomucoid/5 % (w/v) [beta]-lactoglobulin and pure [beta]-lactoglobulin solutions (5 and 10 % (w/v)) with subsequent analysis by rheological measurement, ultrasonic spectroscopy, scanning electron microscopy, and sodium dodecyl sulfate polyacrylamide electrophoresis. For the three systems, the dynamic modulus of the mixed-protein sample was smaller than that of either of the two pure [beta]-lactoglobulin samples. Although ultrasonic-relative velocity temperature sweeps for all samples showed that the relative velocities decreased with increasing temperature, the gradient values differed. Namely, the decrease for the mixed-protein sample (12 m/s) was intermediate between those of the pure [beta]-lactoglobulin systems. Ultrasonic attenuations of all samples increased with increasing temperature, and the absolute attenuation value of the mixed-protein sample was also intermediate between those of the two pure [beta]-lactoglobulin samples. Electrophoresis performed with or without 2-mercaptoethanol suggested that ovomucoid forms an aggregate with [beta]-lactoglobulin via intermolecular disulfide bonds. Together, these results suggest that ovomucoid has a synergistic effect on [beta]-lactoglobulin gelation despite the great heat stability.