Foods are frequently subjected to dynamic loading during harvesting, handling, transportation, and processing. Accurate prediction of dynamic responses of foods under these loading conditions requires better understanding of their dynamic visco-elastic properties. In this article, dynamic equilibrium was determined according to sinusoidal stress-strain. When a visco-elastic specimen is subjected to a sinusoidal varying stress, the resulting strain will be a sinusoidal response of the same frequency as the stress, out of phase by a lag angle. Experiments were conducted to measure the complex modulus of intact Daguanshan peaches and Luyu pears, the phase angle by which the strain lags the stress, and their relationship with initial pre-loading and vibration input power over a range of frequencies. Both the complex modulus and the phase angle increased as the frequency increased from 20 to 200Hz. Initial pre-loading had a significant effect on the complex modulus, but not on the phase angle. Vibration input power had no significant effect on the complex modulus and phase angle. The phase angle depends not only on internal friction but also on the inertia of intact fruit.

An experimental system was set up to generate the impact force, measure the response wave signal, and analyse the frequency spectrum for physical property detection of biological product. The egg dynamic resonance frequency was obtained through the analysis of the dynamically measured frequency response of an egg excited by pendulum. The effects of excitation point, detected point, impact intensity, excitation material, egg mass, egg density, shell stiffness and shell crack on the dominant frequency were analysed. The results showed that the dominant frequency was significantly affected by the shell crack, shell stiffness, egg mass and egg density, and not significantly affected by excitation point, detected point, excitation velocity and impacting material. The dominant frequency increased with increasing of shell stiffness or egg density, and decreased with increase of the egg mass. The coefficient of determination (R2) of the quadratic relationship between the dominant frequency and the three egg physical properties was 0.62-0.68.

An experimental system was set up to generate the impact force, measure the response signal and analyse the frequency spectrum for physical property detection of biological products. The pear dynamic resonance frequencies were obtained based on analysis of the dynamically measured frequency response of an excited pear with changes in the excitation points, the detection points, the impact intensity and the excitation material, and under different pear firmness and mass conditions. As a result of the analysis, it was found that the dominant frequency was significantly affected by the pear firmness and mass. The excitation point, the detection point, the excitation intensity and the impacting material did not significantly affect the dominant frequency. The dominant frequency increased with increasing pear firmness and decreased with increasing pear mass. A good relationship was obtained between the dominant frequency and the pear firmness or the pear mass, and the firmness index regressed on the Magness-Taylor firmness also showed a good relationship.

Little detailed information is available on the microwave drying characteristics of potato and the use of different microwave powers to dry food products. Experiments were conducted to study the microwave drying characteristics and the dried quality of potato. The study focuses on describing the microwave drying characteristics of potato and discussing the effect of sample thickness, drying power and mass. The results show that if the power level increases, the mass load decreases and the thickness of the sample decreases, the dehydration rate increases and the drying energy consumption decreases. There are two falling rate periods during microwave drying of potato: the first falling rate period is for a moisture content of more then 1.1 (dry basis, DB); the second falling rate period is for a moisture content of less than 1.1 (DB). The same water loss will consume more energy when the moisture content is less than 1.1 (DB). A two-stage drying process was employed during microwave drying of potato. The microwave power of the first drying stage differed form that of the second drying stage. The moisture content of the breakpoint for the conversion of the first drying stage into the second drying stage is a moisture content of 1.1 (DB). A quadratic orthogonal regression experiment was conducted, and the effects of slice thickness, the first drying load power and the second drying load power on sensory quality, the rehydration ratio and the energy consumption rate were established. The slice thickness, the first drying load power and the second drying load power linearly affected the three indices. The effect of the product of the second drying load power and the potato slice thickness on the rehydration ratio and the energy consumption rate is significant. The optimum drying parameter combination for the three indices was obtained. The rehydration ratio of the dried products decreased with an increase of the second drying load power and the slice thickness. The concave curves of the sensory quality versus the three factors were shown.

Few studies on the irradiation effects on dehydration characteristics and quality of dried-product ha ve been reported in the past three decades. This study focuses on drying characteristics of bio-products by hot-air after they are pretreated by gamma irradiation. Experiments were made to study the influence of different irradiation dose, air temperature, slice thickness of apple on the ehydration rate, and appearance quality (L-values), vitamin C content, and the rehydration ratio of dried apple. A conclusion is reached that the three factors of irradiation dose, hot-air temperature, and initial slice thickness significantly affected the four indices of appearance quality (L-values), vitamin C content, dehydration rate and rehydration ratio.