Submitted to: Journal of Food Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2007
Publication Date: 4/9/2007
Citation: Guo, W., Nelson, S.O., Trabelsi, S., Kays, S.J. 2007. 10- to 1800-mhz dielectric properties of fresh apples during storage. Journal of Food Engineering. Interpretive Summary: Techniques for nondestructive determination of quality of agricultural products are helpful to producers, handlers and processors, those marketing the produce, and consumers. Visible and physical characteristics of many fresh fruits and vegetables are available for correlation with quality, and some of these, such as color, size, weight, density, elasticity, and firmness are used in automatic sorting of some produce into different categories for the market. Electrical properties of fresh fruits, known as dielectric properties, can be rapidly sensed with suitable measurement instruments that employ radio-frequency (RF) electric fields for this purpose. Therefore, if adequate correlations can be found between the dielectric properties of such fruits and their quality factors, it may be possible to develop new instruments for rapid nondestructive quality determination. In new exploratory studies, the dielectric properties of fresh apples of three varieties were measured at 24 degrees C over 10 weeks in storage at 4 degrees C to determine whether these properties might be used to determine quality factors such as soluble solids content (SSC), firmness, and moisture content. The dielectric constants and dielectric loss factors at 51 frequencies from 10 to 1800 MHz were determined for external surface and interior tissue measurements along with moisture content, firmness, and SSC (sweetness) of juice expelled from the internal tissues. These new data are being reported for the benefit of other scientists and engineers, although no strong correlations were discovered that might be useful for detecting the quality characteristics of fresh apples. Further research is needed to assess the potential for sensing quality of apples through their dielectric properties for the benefit of growers, handlers, marketers and consumers.
Technical Abstract: The dielectric properties of fresh apples of three cultivars were measured at 24 degrees C over 10 weeks in storage at 4 degrees C to determine whether these properties might be used to determine quality factors such as soluble solids content (SSC), firmness, moisture content and pH. The dielectric constants and dielectric loss factors at 51 frequencies from 10 to 1800 MHz were determined for external surface and interior tissue measurements along with moisture content, firmness, and SSC and pH of juice expelled from the internal tissues. Dielectric properties of the three apple cultivars are presented graphically for all frequencies, and correlations between the dielectric properties and measured quality factors are discussed. Although a high correlation was observed in a linear relationship between the dielectric constant divided by SSC and the dielectric loss factor divided by SSC in the complex-plane, the SSC was not predicted well from that relationship, and no high correlations were found between the dielectric properties and SSC, moisture content, firmness, or pH. The dielectric constant and loss factor remained essentially constant during the 10-week storage period.