Effect of environmental water activity on microbial inactivation by intense pulsed light (IPL)

In this study, the effect of environmental a_w on microbial inactivation by intense pulsed light (IPL) was investigated. Three different microorganisms (Gram-positive bacteria, Gram-negative bacteria, and yeast) were used as test organisms. The effect of environmental a_w was assessed by irradiating each microbial suspension in sodium chloride solutions with different environmental a_w levels (0.99-0.80). As the a_w decreased, the aggregation of intracellular material of cell interior was changed and the cell number was increased. However, there was no significant difference in microbial reduction according to the a_w after the 0.23-3.05 J/cm² of IPL treatment. It was confirmed that yeast had the highest resistance to IPL because of the differences in cell structure and cell wall components between yeast and bacteria. Additional research is needed to clearly understand the inactivation mechanism according to the type of microorganism by controlling a_w using various solutes.