Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2007
Publication Date: 6/20/2007
Citation: Wen-Chuan, G., Nelson, S.O., Trabelsi, S., Jones, D.R. 2007. 10- to 1800-mhz dielectric spectroscopy of eggs in storage. Journal of Food Science.
Interpretive Summary: The electrical characteristics of agricultural products known as dielectric properties can be useful for rapidly and nondestructively sensing some quality attributes such as moisture content. The dielectric properties of foods are also useful in dielectric or microwave heating applications in the food industry. Some dielectric properties of eggs have been studied in connection with microwave heating for cooking or processing eggs. However, the dielectric properties of eggs have not been explored for purposes of sensing quality. Therefore, some basic measurements were conducted to determine the dielectric properties of egg albumen and egg yolk in the frequency range from 10 to 1800 MHz and to learn what changes in dielectric properties might occur in eggs during storage. Two quality measurements for eggs, the Haugh unit and the Yolk Index were also measured for the same eggs in the study. These two quality index values decreased as the eggs were held in storage at 15 degrees C. The dielectric properties also showed some changes with storage over a 5-week period, but they did not correlate well with the decrease in quality of the eggs. However, the study was useful in characterizing the dielectric properties of egg albumen and egg yolk during storage and in determining the penetration depth of electromagnetic waves in this frequency range (10 to 1800 MHz)for albumen and yolk. Further research is needed to assess the dielectric properties of eggs for potential use in nondestructive quality sensing for benefit of producers and consumers.
Technical Abstract: The dielectric constant and loss factor of egg albumen and egg yolk during 5 weeks of storage at 15 degrees C were measured at 24 degrees C over the frequency range from 10 MHz to 1800 MHz. Moisture and ash contents of albumen and yolk, as well as Haugh unit and yolk index were also measured. The dielectric constant and loss factor of albumen were higher than those of yolk. Linear relationships were evident between the log of frequency, below about 1000 MHz, and the log of loss factor of albumen as well as that of yolk. The dielectric constants of albumen and yolk at 10 MHz were lower than those of fresh albumen and yolk when eggs were stored at 15 degrees C for one week. However, these dielectric constants rose when the eggs were stored for two weeks. Storage had very little influence on the loss factor. In general, the moisture content of albumen and ash contents of albumen and yolk decreased as eggs aged. The moisture content of yolk increased with storage. The freshness qualities, Haugh unit and yolk index, decreased as egg aged also. No obvious correlation between dielectric properties and moisture content, ash content, Haugh unit, or yolk index was observed. Penetration depth for the yolk was larger that for albumen. However, the storage had very little influence on penetration depth. The factors that influence dielectric properties of eggs during storage, and correlations between dielectric properties and internal qualities are discussed.