ARS | Publication request: Effect of surface roughness on retention and removal of Escherichia coli O157:H7 on surfaces of selected fruits

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 2, 2009
Publication Date: March 15, 2009
Citation: Wang, H., Feng, H., Liang, W., Luo, Y., Malyarchuk, V. 2009. Effect of surface roughness on retention and removal of Escherichia coli O157:H7 on surfaces of selected fruits. Journal of Food Science. 74(1):E8-E15.

Interpretive Summary: Recent food-born illness outbreaks associated with the consumption of fresh produce highlight the importance of ensuring food safety of fruits and vegetables. Produce surface topographies vary greatly in chemical, physical, and structural properties; yet little scientific information exists as to how produce surface characteristics affect the retention and removal of disease-causing microorganisms. This study developed a novel method to quantitatively measure the surface roughness of fresh produce using an advanced microscopic technique, and examined the effect of surface characteristics on the retention and removal of bacteria on apples, avocadoes, oranges, and cantaloupes. We found that bacteria attached less on smooth fruit surfaces than they did on rough surfaces, and bacteria attached to smooth surfaces were also easier to remove during produce wash than those on rough surfaces. These findings provide important information to produce breeders for developing new crops to advance food safety and to the industry for developing new antimicrobials to achieve maximum reduction of disease-causing bacteria.

Technical Abstract: This study was undertaken to evaluate the effect of surface roughness on the attachment and removal of Escherichia coli O157:H7 on selected fruit surfaces. A new method to determine surface roughness was developed using confocal laser scanning microscopy (CLSM). A series of 2-D layered images were taken by CLSM optical slicing of the surfaces of Golden Delicious apples, Navel oranges, avocadoes and cantaloupes. The average roughness (Ra) of the fruit surfaces was assessed by reconstructing a series of 2-D images into 3-D images. A cocktail of five E. coli O157:H7 strains were spot inoculated onto fruit skin surfaces with different Ra. The fruits were then treated with acidic electrolyzed water (AEW), peroxyacetic acid (POAA), and sterile de-ionized water. Aluminum stubs with different Ra values as a model system were also spot inoculated with E. coli O157:H7 and subjected to a sonication treatment. Test results indicated that there was a positive linear correlation between Ra and adhesion rate of E. coli O157:H7, and a negative correlation between Ra and the efficacy of inactivation by AEW and POAA on fruit surfaces. A linear increase of residual bacteria population with increased surface roughness of aluminum stubs was also observed. The relationship between surface roughness and surface hydrophobicity was linear for the aluminum stubs, but was quadratic for the four fruits. The environmental scanning electron microscopy images showed that bacteria tended to attach to or be entrapped in the grooves or cavities of fruit skins, which provided protection to the cells against washing treatments.