静压力对苹果介电特性和胞内水分的影响

The influence of static pressure on dielectric property and intracellular moisture of apple

对苹果施加不同大小静压力,同时利用平行板电极法监测其介电参数,用针状电极监测其电阻抗图谱,根据Hayden等效电路模型计算分析了胞内电阻、胞外电阻和细胞内、外液体积分布的变化。结果表明:静压力小于120 N,相对介电常数和损耗因子随静压力的增大而非线性增大,大于120 N后线性增大;同一静压力下,相对介电常数随加载频率增大而变小,损耗因子则在加载频率为20 k Hz时有极小值;随静压力增大,苹果组织胞内电阻增大,胞外电阻在小于120 N阶段基本保持水平,大于120 N后开始增大。在静压力增大至250 N的过程中,细胞外液体积百分比由5.69%增加至9.22%,苹果相对介电常数、损耗因子和细胞外液体积百分比之间呈极显著正相关,相关系数大于0.94,说明细胞外液的体积变化是引起果品介电参数变化的主要原因。本研究有望为果品受压过程中内部生理状态的同步监测研究提供新思路,也将为采用介电特性法快速评价其损伤提供理论指导。

The dielectric parameters of compressed apple in various pressures were monitored by parallel plate electrode and the electrical impedance spectroscopy（ EIS） was monitored by stainless steel needle electrode and the resistance of intracellular fluid and extracellular fluid and the change of volume distribution of intracellular fluid and extracellular fluid were calculated by Hayden equivalent circuit model. The results were as follows： relative dielectric constant and loss factor were nonlinear increase with static pressure increase when the pressure was less than 120 N,and were linear increase under the pressure of more than 120 N.Under the same static pressure,relative dielectric constant decreased with the loading frequency increase and loss factor existed in minimum value at 20 k Hz. With the static pressure increasing,the intracellular resistance increased,and extracellular resistance remained unchanged less than 120 N then increased. During static pressure increase to 250 N,the volume percentage of extracellular fluid increased from 5.69% to 9.22%. The relative dielectric constant,loss factor and the volume percentage of extracellular fluid was significant positive correlation and correlation coefficient was more than 0.94,in which account for the volume percentage of extracellular fluid was the main reason of dielectric parameters change.The work is hopeful to find a new idea for simultaneous monitoring physiological state of compressed fruit,and also provides theoretical guidance for rapid revaluation damage degree of fruit and realizing fruit grading by dielectric property.