In a study published in the Journal of Food Science, researchers used confocal laser scanning microscopy (CLSM) to show that surface roughness of fruits allows bacteria to attach and is thus harder to remove. 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. Among the four fruits, apples had the smoothest surface, while the cantaloupes had the highest Ra value.
After the surface roughness was determined, a cocktail of five Escherichia coli strains were spot inoculated onto the fruit skin surfaces. The fruits were then treated with acidic electrolyzed water (AEW), peroxyacetic acid (POAA), and sterilized deionized water. Results showed that the adhesion rates of E. coli cells increased with Ra values of the four types of fruits treated with sterilized deionized water, AEW, and POAA. Once a bacterium was attached to a surface, the irregularity or defects on the surface could provide protection against a washing treatment. In addition, the bacterium becomes more firmly attached to the surface the longer it remains.
The researchers concluded that the CLSM technique is a feasible tool to study the contribution of surface topography of fruits and vegetables to the attachment and removal of microorganisms on food surfaces. This could be beneficial to the produce industry in its effort to enhance microbial safety in produce production. Additionally, it was shown that an increase in surface roughness would introduce protection to microbes entrapped on fruit surfaces, resulting in reduced washing efficacy.