Characterizing Intense Pulsed Light-Elicited Effects on Escherichia coli and Non-Fat Dry Milk Through Metabolomic and Chemometric Analysis

Abstract

Disinfecting powder food is challenging due to their low water activity. Intense-pulsed light (IPL) is advantageous in achieving efficient bacterial reduction. Its mechanisms of mediating bactericidal effect has been characterized as inducing DNA damage and disrupting cell structure integrity. A novel IPL platform is being constructed and studied to achieve high disinfecting efficacy while maintaining the physiochemical properties of the powder food. However, little is known about its influence on cell metabolism, which is essential for cell survival and growth. E.coli K-12 culture from overnight incubation were treated with a bactericidal dose of IPL for different durations. After centrifugation, the metabolites in bacterial pellets were extracted by a mixture of chloroform, methanol, and water. Aqueous and lipid extracts were examined by liquid chromatography-mass spectrometry (LC-MS)-based metabolomic analysis. The principal components analysis (PCA) of LC-MS data indicated that the metabolome of E. coli was dramatically affected by IPL treatment in a time-dependent pattern. Multiple nucleotides, antioxidants, and membrane components, including adenosine monophosphate, glutathione, and menaquinone-8, were identified as the metabolites sensitive to IPL treatment. These markers revealed IPL-induced membrane damage and oxidative stress. Additional markers suggest IPL hindered ability of repairing DNA damage. New information from untargeted metabolomic analysis provides useful insights on the mechanism of IPL-elicited bactericidal activities. An ideal IPL treatment is expected to achieve pasteurization with minimal influences on physical, chemical, and nutritional properties of powdered food. While IPL showed effective bactericidal effect, it is also essential to evaluate its influence on the food matrix. IPL-irradiated non-fat dry milk was prepared by solvent extraction and acid hydrolysis, and then examined by liquid chromatography-mass spectrometry (LC-MS) analysis. Targeted and untargeted chemometric analysis were performed to determine the chemical compositions of prepared samples and the effects of IPL treatment. Targeted chemometric analysis indicated that IPL treatment in this study did not significantly affect the amino acid composition of non-fat dairy milk powder. However, the multivariate models constructed by untargeted chemometric analysis of extracted samples revealed the dose-dependent chemical changes after IPL treatment. IPL treatment directly degraded riboflavin, and led to formation of peptides as a result of photolysis of milk proteins. Untargeted chemometric analysis on the chemical effects of IPL treatment will provide useful information to guide the development of IPL disinfection technology.