Relationship between Dielectric Properties, Physiological Properties, and Internal Qualities of Pears during the Late Growth Stage
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Abstract:
To understand the relationship of dielectric properties and physiological properties with the internal qualities of pears during the late growth stage, the open-ended coaxial-line probe technique was used to measure the permittivities (relative dielectric constant and dielectric loss factor ) of pears over the frequency range of 20~4500 MHz during the last 2 months of the ripening period, along with the physiological properties (amount of released ethylene and respiration intensity) and internal qualities (soluble solid content [SSC], firmness, and moisture content). Over the frequency measurement range, decreased with increase in frequency, and had maximum and minimum values at approximately 25 MHz and 1300 MHz, respectively. Over time, and increased after the initial decrease, and sugar content and firmness decreased generally. The respiration peak occurred before the peak of released ethylene, and the time when the peak of released ethylene appeared was the same as the turn point when permittivities changed from decreasing to increasing. Apparent linear relationships of the permittivities with SSC and firmness were not found. The results indicate that the dielectric properties of pears are the reflection of physiological properties and that the maturity of pears can be determined on the basis of values of permittivities. However, it is difficult to use the value of a permittivity at a single frequency to assess the internal qualities of pears.
