发育后期苹果的介电特性与理化特性的关系

为了解发育后期苹果的介电特性、生理特性和内部品质的变化规律以及三者之间的关系，采用同轴探头技术测量发育后期3 个月内‘富士’苹果在20～4 500 MHz间的相对介电常数ε’和介质损耗因子ε”，同时测量苹果果实的生理特性（乙烯释放量和呼吸强度）和内部品质（可溶性固形物含量（soluble solids content，SSC）、硬度、pH值和含水率）。结果表明：ε’随频率的增加而减小，ε”在2 000 MHz附近存在极小值；随着果实逐渐发育成熟，ε’和ε”逐渐减小。整个发育后期，果实的SSC和果汁的pH值呈上升趋势，硬度呈下降趋势；乙烯释放高峰出现在2 个呼吸高峰之间。ε’和ε”与SSC、硬度和pH值在特定的频率范围内存在较好的线性相关性。研究说明，苹果的介电特性是生理特性与内部品质的综合反映，根据介电参数值判断苹果的成熟情况以及用单一频率下的介电参数值评价苹果的内部品质均可行。

Relationship between Dielectric Properties and Physicochemical Properties of Apples during Late Developmental Period

To understand the changing patterns of dielectric properties, physiological properties and internal qualities
during the late developmental period of apples and to illustrate the relationship between them, open-ended coaxial-line
probe technology was used to measure the dielectric constant ε’ and dielectric loss factor ε” of apples over the frequency
range of 20?4 500 MHz during the last three months of fruit development, along with the physiological parameters (the
amount of released ethylene and respiration intensity) and internal qualities (soluble solids content (SSC), firmness, pH and
moisture content). The results showed that ε’ decreased with increasing frequency, and ε” had minimum values at around
2 000 MHz. During fruit development, the dielectric constant ε’, dielectric loss factor ε” and firmness decreased, while SSC
and pH increased with maturity. The peak of released ethylene was found between two respiration peaks. There were good
linear relationships among dielectric constant ε’, dielectric loss factor ε”, SSC, firmness and pH in some frequency ranges.
This study indicated that the dielectric properties were a comprehensive reflection of physiological properties and internal
qualities. The maturity of apples could be judged by dielectric constant ε’ and dielectric loss factor ε”. It is feasible to assess
internal qualities of apples using a permittivity value at a given frequency.