Blanching of potato with superheated steam and hot water spray

A heating system using superheated steam (SHS) and a spray of hot water microdroplets (WMD) has been developed to prevent drying of food material during SHS heating. Blanching of potato was examined with the new system (SHS + WMD), SHS, and hot water. In SHS + WMD heating, a mixture of SHS at 115 °C, 2.46 kg/h flow rate and hot water at 0.54 kg/h was used. In SHS heating, the flow rate and temperature of the SHS were 3.0 kg/h and 115 °C. The temperature of the hot water was approximately 100 °C. Potato tissue processed with hot water became soft and brittle, and its brightness and chromatic quality decreased due to absorption of water and dissolution of solid content to the water. In contrast, these quality changes were prevented in SHS + WMD and SHS heating. Heat transfer by SHS was enhanced by the presence of WMD, presumably because the water layer formed on the potato by condensation of SHS was stirred and its thermal resistance was decreased by collisions of WMD with the potato. The mass of potato processed with SHS + WMD was almost constant during the heating, while the relative mass of potato processed with SHS decreased to 96.7% with 16 min of heating.