Dielectric properties of powdered infant formula milk as influenced by frequency, temperature and main components

Abstract.

Powdered infant formula milk (PIFM) may be contaminated by Enterobacter sakazakii during packaging process. In order to develop effective in-package pasteurization treatments of PIFM based on radio frequency (RF) and microwave (MW) energy, dielectric properties of PIFM samples at different frequencies (10 MHz - 3 GHz), densities (0.36-0.54 g/cm3), temperatures (20°C-80°C), moisture contents (2.5%-5.5% w.b.), were measured by an open-ended coaxial-line probe and impedance analyzer. And powdered infant formula milk model mainly consisted of whey protein (10%-18%), fat (20%-31%), lactose (48%-60%) and moisture (2%-4% w.b.) were also measured in order to develop a model to describe the relations between dielectric properties and investigated factors such as main components and temperature for PIFM. The effects of frequency, density, temperature, and moisture content on PIFM dielectric properties were analyzed. Both dielectric constant and loss factor increased with increasing frequency firstly and then decreased. Dielectric constant increased with increasing density and main components, while dielectric loss factor decreased with increasing fat content and increased with density and temperature to a certain level and then decreased. Quadratic and linear relationships were observed, respectively, for temperature and density, components (moisture, whey protein, fat and lactose) content at two specific frequencies. Whey protein and lactose exerted positive effect on dielectric properties due to ionic conduction, while fat exerted negative effect due to its weak polar characteristics. Moisture content of PIFM and RF treatment temperature can be controlled about 3.5% and 65°C to realize relative uniform heating. It can be concluded that low frequencies, like RF, may provide potential large-scale industrial in-package pasteurization treatment of PIFM with acceptable uniformity and throughputs.