Application of microwave sensors to potato products

Abstract

The first microwave measurement techniques uses an open ended coaxial probe with a purposely built sample holder to measure the dielectric properties ofpotato products from 500 MHz to 1 GHz. The second system utilises awaveguide cell with a purposely built sample holder to characterise potatoproducts from 2.4 to 3.5 GHz. Common British varieties of raw potatoes such asEstima, King Edward and Maris Piper are used in this study. The two microwavemeasurement techniques are also used to measure the dielectric properties ofpotato products at elevated temperatures for these frequency ranges. Bothmeasurement techniques are also used to study the effect of storage temperatureon the dielectric properties of Saturna raw potato. For this part of study, it isconcluded that the microwave measurement techniques are unable todiscriminate between potatoes that had a storage history of different temperatureprofiles. On the other hand, waveguide cells and open ended coaxial probes areable to measure the dielectric properties of raw potato, partial cooked fried potatoand fried potato at the 500 MHz to 1 GHz and 2.4 GHz to 3.5 GHz frequencyrange. The measurement results show that both dielectric constant and lossvalues of fried potatoes decreased with frying time, due to the reduced moisturecontent during the frying process. Furthermore, the dielectric loss behaviour ofraw and fried potatoes is dominated by the effect of the ionic conductivity atfrequencies lower than 1 GHz. An apparatus has been designed and built in orderto measure the dielectric properties of potato for both frequency ranges as afunction of temperature. In the subsequent measurements it is found that thedielectric properties of potato products at elevated temperatures also depend onfrequency and moisture content. For high moisture content potato (~> 70 %), at2.45 GHz both the dielectric constant and loss are found to decrease withtemperature, whereas at 915 MHz the dielectric constant decreases but the lossincreases for the moisture content above 30%. For the intermediate moisturecontent (10%

Date of Award	1 Aug 2010
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Andrew Gibson (Supervisor)