Assessing the supercooling of fresh-cut onions at -5°C using electrical impedance analysis

Abstract

We supercooled fresh-cut onion at -5°C for 12 h. After supercooling, the electric impedance properties of the samples were evaluated by electrical impedance spectroscopy over the frequency range of 42 Hz - 5 MHz. The time-Temperature profiles of samples indicated that the freezing point and supercooling point were -2.3°C 0.7°C and -6.9°C 1.0°C, respectively. The results indicated that 34 of the 36 supercooled samples exhibited a definite circular arc in the Cole-Cole plot, which suggested that the cell membrane remained intact during supercooling. In the other two samples which did not exhibit a definite circular arc, the cell membrane had sustained serious damage during supercooling. Furthermore, there was large difference in drip loss percentage between supercooled samples exhibited a definite circular arc in the Cole-Cole plot and samples not exhibiting a definite circular arc. Our results suggest that fresh-cut onions can be supercooled at -5°C.