Dielectric properties at frequencies from 0.2GHz to 20 GHz of mashed mesocarp of oil palm fruits at various stages of maturity are presented.

Measurement of microwave permittivity was done by using open-ended coaxial line probe and automated network analyzer. The accuracy of measurement is about 5% for dielectric constant, ε’ and 3% for dielectric loss factor, ε”. Results of measurement show that the ionic conductivity dominated in the region less than 3GHz, while above 3GHz the dipole orientation of water molecules becomes dominant. The effect of ionic conductivity is higher in young fruit and decreasing as degree of maturity increases.

Permittivity of oil palm mesocarp over the frequency range was found to increase with moisture content. A significant variation of ε’ and ε” with maturity at 0.2GHz and 10GHz respectively make it suitable to form a maturity index as suggested by Nelson et al.. With moisture content ranging pom 25% to 85%, the ε’ at 2GHz varies from 11 to 61 and the ε” varies from 2.1 to 24.6 at 10 GHz. Based on the above values the permittivity-based maturity index for young and fully ripe fruits are 1 and 0.3 respectively.

The results of the dielectric properties of mashed mesocarp also agree reasonably with predicted values from mixture model especially at frequencies above 3 GHz. At 10 GHz the difference between predicted and measured values are within 5%.

This study gives valuable information for the analysis and design of microwave sensor for quality assessment of the oil palm fruits and could also be used for estimating microwave absorption during fruit sterilization and fruit loosening.