Effects of the high-pulsed electric field pretreatment on the mechanical properties of fruits and vegetables

A high-pulsed electric field (HPEF) technique show potentials to reduce the drying time and energy consumption of a vacuum freeze-drying technique, which can maintain the nutritional and sensory properties of the foods. It is important to understand effects of the HPEF treatment and the optimized operation parameters on changing the mechanical properties of fruits and vegetables for improvement of the vacuum freeze-drying process. The viscoelastic properties of four types of fruits and vegetables with and without the HPEF pretreatment were studied using experimental measurements of the stress relaxation and creep of the fruits and vegetables. The stress relaxation parameters of the fruits and vegetables were estimated according to the Generalized Maxwell model. The values of the equilibrium elastic modulus (E-e) decreased more than 92%, and relaxation time (T) values decreased more than 17%, after HPEF pretreatment. The creep parameters of the fruits and vegetables were estimated according to the Burger four-parameter model. The values of the instantaneous elastic modulus (E-0) decreased more than 70%, the retarded elastic modulus (E-r) decreased more than 92%, and the viscosity coefficient (eta(r)) decreased more than 94% after the HPEF pretreatment. The results showed that the HPEF pretreatment improved the vacuum freeze-drying process.