Blanching of potato with superheated steam containing micro-droplets of hot water

Abstract

A newly developed oven system, which generates superheated steam consisting of micro-droplets of hot water (Aqua-gas) by spraying heated water into a heating chamber, was applied to the blanching of potato. It was thought that the micro-droplets would increase the heat transfer coefficient of the heating medium to the extent that they would prevent the deterioration of foods due to drying during the heating process. Blanching of the potatoes was conducted using Aqua-gas (115°C), superheated steam (115°C) and hot water (100°C). The thermal properties of the heating mediums and the qualities of the potato processed with the heating mediums were compared. Though a greater heat transfer coefficient was measured in the Aquagas, no significant differences were observed in temperature distributions or the progress of peroxidase inactivation among the heating media. Heat transfer simulations showed that the temperature distribution in the potatoes was only dependent upon thermal diffusivity of the potato since the heat transfer coefficients of the heating mediums were sufficient. The potatoes processed with the Aqua-gas and with the super-heated steam were firmer and brighter than the potatoes processed with the hot water. In addition, weight loss of the potatoes was reduced and any Bacillus subtilis would have been sterilized by the Aqua-gas.