Heating rate of egg albumin solution and its change during Ohmic heating

Ohmic heating of egg albumin solution (10 w/v%) was examined at 50-10 kHz under a constant 10 V/cm. The heating rate of the solution was almost constant and increased slightly as the frequency increased. The gel formation was observed at about 75 degrees C and the heating rate increased above this temperature irrespective of the frequency used. The solution and gel showed almost the same impedance at the examined temperature (20-90 degrees C) and frequency (10 Hz-100 kHz). When the concentration of egg albumin was reduced to 2 w/v%, no gel was formed and a constant heating rate at over 75 degrees C was observed. The breaking strength of the gels showed little difference among the gels prepared by boiling water or Ohmic heating. These results suggest that the liquid components are not compartmentalized in the gel and that the sudden increase of heating rate above 75 degrees C was caused by the reduction of heat transfer of the gel at its phase change to the gel. Ohmic heating was also applied to the fresh egg white at the same conditions as that of the egg albumin solution. The fresh egg white did not show any sudden increase of heating rate until it reached 90 degrees C. However, the homogenized fresh egg white and its soluble part separated beforehand showed a slightly reduced heating rate and a sudden increase at about 60 degrees C. These results suggest that the gelatinous component of fresh egg white such as ovomucin represses the transfer of generated heat during Ohmic heating.