| China has a large amount of apple production and a wide planting area, but a low export rate. And the fruit processed to juice is only 20 percent of the total. There is a certain gap with United States and the other developed countries. In order to improve the yield rate of the apple juice and ensure the quality, this article uses the electrical impedance spectroscopy method testing the impedance. And studied the effect of heating pretreatment temperature on the structure and water distribution in apple tissue, the electrical impedance spectroscopy was used to test and fit the data. The fresh Shaanxi White Red Fuji apple were detected and calculated the value of the corresponding electrical properties. Choosing the ‘Hayden model’ as equivalent electrical model this model is composed of three circuit elements with four parameters which are extracellular resistance, intracellular resistance, membrane capacitance and phase angle. The complex nonlinear least square(CNLS) method was applied to the measured data in order to determine the model parameters. At the same time, the internal structure and the water distribution of the cell were detected by electron microscope scanning and nuclear magnetic resonance technology, and the optimum pretreatment temperature was determined. The apple quality prediction model was established by spectrum data and apple quality parameters, and the advantages and disadvantages of different models were analyzed.1) The results indicated that the influence of temperature on apple tissue cells could be divided into 3 stages, <60 degrees, 60-70 degrees, and >70 degrees. The impedance of apple tissues decreased with the frequency increasing, and it decreased significantly when temperature increased to 65 degrees. When the temperature was 65 degrees, it was the critical factor to break the cells, although holding time could increase the permeability of cell membrane. So it was assumed that the thermal damage temperature of apple tissues was 65 degrees which could also be seen from the scanning electron microscope(SEM) pictures. And the extracellular and intracellular resistance, and cell membrane impedance began to change at 65 degrees.2) In order to study the moisture changes of the apples tissue cells during the heating, using cylindrical apple as raw material. Using water bath heating and ohmic heating to pretreatment apple blocks, and using LF-NMR to test the transverse T2 relaxation time and relative peak area to character the apple tissue cell’s water status and different states of the moisture content. And studying the transition process of moisture state. When the temperature of apple tissue is higher than 65 degrees, 90% of the liquid water in the intracellular and the extracellular was migrated outside the cell. Cytoplasmic water’s relaxation time increased and then remained unchanged with the increase of the temperature. The change of vacuole water’s relaxation time was first increased and then decreased with its turning point is 65 degrees. The relaxation time of the ohmic heating process is changed at 65 degrees. The relative peak area of T2 relaxation of low field nuclear magnetic resonance can be used to characterize the moisture content of different binding states. The vacuolar water is the highest. When the heating temperature is lower than 70 degrees, it decreased significantly with the increase of temperature. The cytoplasmic water was lower than that of vacuolar water, showed an upward trend. The water content of cell gap and cell wall is low. Overall, when the temperature is increased to 65 degrees, the damage of vacuolar membrane is large, the transfer of liquid water is large. |
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