Abstract:

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.

Key words: apple, fruit development period, dielectric constant, dielectric loss factor, physiological properties, quality