3 research outputs found
Inactivation Kinetics of Pectin Methylesterase, Polyphenol Oxidase, and Peroxidase in Cloudy Apple Juice under Microwave and Conventional Heating to Evaluate Non-Thermal Microwave Effects
Effect of Electric Field on Pectinesterase Inactivation During Orange Juice Pasteurization by Ohmic Heating
Dielectric properties of almond kernels associated with radio frequency and microwave pasteurization
To develop advanced pasteurization treatments based on radio frequency (RF) or microwave (MW) energy, dielectric properties of almond kernels were measured by using an open-ended coaxial-line probe and impedance analyzer at frequencies between 10 and 3000 MHz, moisture contents between 4.2% to 19.6% w.b. and temperatures between 20 and 90 °C. The results showed that both dielectric constant and loss factor of the almond kernels decreased sharply with increasing frequency over the RF range (10–300 MHz), but gradually over the measured MW range (300–3000 MHz). Both dielectric constant and loss factor of almond kernels increased with increasing temperature and moisture content, and largely enhanced at higher temperature and moisture levels. Quadratic polynomial equations were developed to best fit the relationship between dielectric constant or loss factor at 27, 40, 915 or 2450 MHz and sample temperature/moisture content with R(2) greater than 0.967. Penetration depth of electromagnetic wave into samples decreased with increasing frequency (27–2450 MHz), moisture content (4.2–19.6% w.b.) and temperature (20–90 °C). The temperature profiles of RF heated almond kernels under three moisture levels were made using experiment and computer simulation based on measured dielectric properties. Based on the result of this study, RF treatment has potential to be practically used for pasteurization of almond kernels with acceptable heating uniformity