4.3.2. Methods for sanitation

Disinfection

Many producers and suppliers are committed to good practices to reduce the risk of contamination. Conventional methods to decrease contamination include post-harvest decontamination procedures. However, experiments using standard post-harvest decontamination procedures with solutions containing approximately 20–200 mg ml^-1 free chlorine for various lengths of time found that bacterial numbers were reduced but the treatments did not completely eliminate either the natural microbial population, or human pathogens.

Household natural sanitizers including fresh lemon juice and vinegar have been shown to have some effect in the reduction of Salmonella serovar Typhimurium on rocket leaves and spring onion. A 15 min treatment with 1:1 lemon juice and vinegar reduced viable counts to undetectable levels. Treatment of carrots with this solution reduced Salmonella CFUs to an undetectable level.

Treatment of commercial iceberg lettuce pre-inoculated with natural spoilage organisms with chlorine, ozone or a combination of them reduces the number of viable microorganisms. Additionally chlorine–ozone combinations increase the shelf life of lettuce. No visible changes in rinse water turbidity or reduction in quality are observed during rinsing of the lettuce, indicating applicability to commercial processing.

Ionizing radiation has demonstrated efficacy in reducing microbial contamination. In particular, studies focused on leafy greens have shown multiple log reductions in L. monocytogenes, Salmonella and E. coli O157:H7 when used on various leafy greens, including iceberg lettuce, Romaine lettuce, and spinach.

Biocontrol

An alternative method to reduce contamination would be the use of agricultural practices that encourage growth of competing bacteria within the phyllosphere to reduce the contamination with human pathogens. Various studies suggest that the natural microflora of plants can inhibit the growth of E. coli O157:H7, Salmonella serovars Montevideo and Chester, and Staphylococcus aureus. Pseudomonas and Bacilus species isolated from green pepper, Romaine lettuce, baby carrots, alfafa, and clover sprouts can inhibit the growth of Salmonella serovar Chester and L. monocytogenes. Enterobacter cloacae reduced the colonization of carrots, cress, lettuce, radish, spinach, and tomatoes by E. coli O157:H7 and L. monocytogenes, whereas Enterobacter asburiae decreased their survival on lettuce. Also, growth of Arabidopsis thaliana with E. asburiae in gnotobiotic conditions strongly reduced the root contamination by Salmonella or E. coli O157.

Image-based control

Identification and quantification of plant diseases are required for adequate plant protection, determination of crop losses, and for the design of breeding strategies in agriculture. The potential of image-based analysis in the detection and monitoring of plant disease is well accepted and the use of these techniques to study plant infections with potential human pathogenic microorganisms is a new and developing area. This analysis involves capturing targets arrays of plant production and search of phenotypic marks in plants, which are an indication of phytopathogenic diseases or the development of human pathogens.