Effect of Far-Infrared Irradiation on Pasteurization of Bacteria Suspended in Liquid Medium Below Lethal Temperature

Abstract

The purpose of this study is to examine the influence of far-infrared irradiation on pasteurization of bacteria suspended in liquid medium below the lethal temperature. Under this condition, Escherichia coli and Staphylococcus aureus are injured and killed by far-infrared irradiation. With increase in irradiation power and with decrease in depth of the suspension, the ratio of the number of injured cells to the number of viable cells becomes higher, and the number of viable cells becomes smaller. Moreover, the pasteurization effect can be enhanced by raising the bulk temperature of the suspension. By estimating the temperature distribution within the suspension, it is suggested that the test bacteria are injured and killed in the very thin domain near the surface of the suspension.