Survival of cut cabbage subjected to subzero temperatures

The use of supercooling during preservation has the potential to increase the shelf life of vegetables at subzero temperatures without freezing occurring, and would be a new preservation method for living vegetables. In this study, we measured the survival ratio of cut cabbage (Brassica oleracea var. capitate) subjected to subzero temperatures (-5 or -10°C) by use of ethanol brine for 12 h. Cole-Cole plots of the supercooled samples, including fresh as well as dead samples (stored at -80°C for 12 h), were generated using electrical impedance spectroscopy. Cell viability was quantitatively determined by the triphenyl tetrazolium chloride method (physiological index for evaluation of freezing injury in plant tissue). The results of the fresh samples showed that the Cole-Cole plot described a circular arc, and high values for cell viability were maintained. With regard to the dead samples, no circular arc was found in the Cole-Cole plot, and little cell viability was obtained. Thus it can be said that electrical impedance spectroscopy is a rapid and effective method for evaluating survival after supercooling. Our test indicated that the survival percentages of supercooled samples were 100% and over 30%, for -5 and -10°C. Furthermore, samples that were dehydrated before supercooling were used for the preservation test at -10°C. The survival percentage of 30% (w/w) dehydrated samples was higher compared with supercooled samples, although the difference was not statistically significant.