Role of multiscale leaf surface topography in antimicrobial efficacy of chlorine-based sanitizers

Abstract

Conventional washing and sanitizing approaches for leafy greens provide limited inactivation of bacteria on leaf surfaces. For a quantitative understanding of the barriers to bacterial inactivation on leaf surfaces, this study develops a numerical simulation approach based on mass transport and surface reaction kinetics. Two specific sections of a leaf surface, i.e., a local region with “macroscale” veins and a local region with “microscale” contours without veins, were selected for numerical simulation. This study also evaluates the effectiveness of a novel sanitizer composition using chlorine bound with yeast microcarriers. This composition reduces the nonspecific reactivity of free chlorine and promotes targeted binding of the microcarriers to bacteria to enhance the inactivation of leaf-attached bacteria. For experimental validation, baby spinach leaf sections with and without macroscale veins were inoculated with 5 log CFU/cm2 of E. coli and treated with these chlorine-based sanitizers for 30 min, and the surviving bacteria on the leaf samples were enumerated by plate counting. Both simulation and experimental results show ∼0.7 log reduction of inoculated bacteria by free chlorine treatment for a local region representing macroscale leaf surface geometry. However, no significant bacterial inactivation was observed on the microscale leaf surface geometry. In contrast, yeast-bound chlorine improved bacterial inactivation in both macro-and microscale geometries based on enhanced stability and bioaffinity. Overall, this study illustrates the influences of heterogeneity of leaf surface topography and chlorine delivery systems on the inactivation of leaf-attached bacteria.