4d.Progress report.
This report serves to document research conducted under a Specific Cooperative Agreement between ARS and the University of Illinois. Additional details of this research can be found in the report for the parent project 1275-42000-004-00D, entitled "Microbial Food Safety of Fresh and Fresh-cut Produce." The agreement was formalized in 2004 by the recruitment of one Visiting Scientist to undertake the studies on the dual controls of browning reaction and pathogen growth of fresh-cut apples, and the quality improvement of fresh-cut produce.

The inactivation mechanism of sanitizing agents on E.coli cells was investigated with atomic force microscopy (AFM). We found that peroxyacetic acid (POAA) treatment caused separation of cell membranes from cell cytoplasm and significant changes in surface topography and morphology. This indicates that electrolyzed water (AEW) and chlorine treatments inactivated E.coli cells by damaging cell surfaces. Adhesion force between the AFM tip and cell surface sharply decreased when morphological changes were observed. The difference in cell morphology between E. coli cells treated with POAA and that with AEW and chlorine may indicate a different bactericidal mechanism. This information is of importance to the future development of effective sanitizers to reduce microbial populations and maintain food quality and safety of fresh produce.

Surface roughness and topography of fresh produce affects the attachment and removal of human pathogens. A novel scientific method was developed to objectively quantify the surface roughness of fresh produce. A confocal laser scanning microscope was used to obtain a series of 2-D layered images by optically slicing the surface of a selected fruit. Average surface roughness (Ra) was then determined with MetLab software from a 3-D image reconstructed from the 2-D layered images. A positive linear correlation was found between surface roughness and microbial reduction rates from both metal and produce surfaces. These findings will provide insight into the mechanism of microbial attachment and removal and help to find means to improve produce washing efficiency.