Heating patterns of white bread loaf in combined radio frequency and hot air treatment

This research investigated heating uniformities of prepackaged bread loaf using combined radio frequency (RF) and hot air treatments to reduce mold growth. Experiments were conducted in a 6 kW, 27.12 MHz pilot-scale RF system. Effects of the gap between two RF plate electrodes, horizontal and vertical locations of bread loaf, as well as running speed of conveyor belt were studied. When the bread loaf was located in the center plane between the two electrodes 202 mm apart, and on a conveyor belt moving at a speed of 1 cm/s to reach a minimum sample temperature of 58 °C, the temperature distribution within each slice was relatively uniform, with less than a 5 °C difference. The cold spot was located at the core of the bread loaves. Higher surface temperature should be useful to assist in inactivation of molds that are commonly vegetated on the surface of the whole loaf.

► Bread vertical heating uniformity was improved by changing gap between electrodes in RF treatments.
► Products should be placed midway between two electrodes to eliminate edge heating.
► Conveying speed in the tested range did not influence heating uniformity obviously.
► The cold spot was at the core of bread loaf in combined RF and hot air treatment.