High temperature short time processing (sterilization and pasteurization) by continuous flow system, which consists of heat exchangers and a holding tube, offers shelf stable foods of high quality. Since the lethal effect for food is calculated based on the temperature histories, the engineering knowledge such as flow behavior and heat transfer is indispensable. To ensure microbial safety, thermal schedule to sterilize all parts of the food under the worst condition must be established. The continuous flowing sterilization of liquid food such as beverage has already been widely used as useful producing method. However, the lethal effect might be underestimated because the understanding of their flowing characteristics is insufficient. There are many difficulties with sterilization of the food containing particles. The evaluation of flow velocity distribution of the particles and the boundary heat transfer coefficients between the particle and fluid are especially important to calculate the lethal effect.
In order to clarify the rheological characteristics of the coagulated egg processed by ohmic heating, heating rate of liquid egg containing 0-2% salt was investigated under conditions of applied voltages ranged from 19 to 73 V and constant frequency of 60 Hz, and then the rheological behavior of coagulated egg was studied with stress relaxation tests in which the material was compressed to a constant strain. The average heating rate of liquid egg was directly proportional to the square of applied voltage, and it increased linearly with increasing salt content. The stress relaxation of coagulated egg consisted of three steps that could be expressed with a five-element Maxwell model. Analysis of the stress-relaxation of coagulated egg showed that the viscosity decreased, while the elasticity increased with increasing salt content in the range of 0-0.5%. However, there was no apparent effect of applied voltage on the viscoelasticity of coagulated egg.