4.3. Food plant sanitation

4.3.1. Sources of contamination

Assuming the bacteria are not internalized in the plant tissue, surface sanitisation is normally an effective way to remove pathogenic bacteria from products. Many reports show that contaminated surfaces are most likely the source of product contamination, and that the risk of contamination is highest between the primary trimming and chopping and the packaging stages. Sources of contamination that should be considered are: hands, gloves, and personal protective equipment; slicers; conveyors; washing tanks and wash water; holding containers and racks for packaging, and packaging equipment.

Cross-contamination is one of the main risks to food safety during processing. Cross-contamination can occur in three main ways:

• Food to food. Food can become contaminated by bacteria from other foods. This type of cross-contamination is especially dangerous if raw foods come into contact with cooked foods.
• People to food. People can be a source of cross-contamination to foods, when good hygienic practices are not performed by food handlers, such as handling foods after using the toilet without first properly washing hands, touching raw meats and then preparing foods without washing hands between tasks, using an apron to wipe hands between handling different foods, or wiping a counter with a towel and then using it to dry hands.
• Equipment to food. Contamination can be passed from kitchen equipment and utensils to food. This type of contamination occurs because the equipment or utensils are not properly cleaned and sanitized between each use.

Temperature during storage and distributioncan also be a source of contamination. Disease-causing pathogens can grow well in food when it is kept at temperature between 5°C and 57°C, which is known as the temperature danger zone. If food is kept at these temperatures for more than 4 hours, pathogens can grow to levels high enough to cause serious food-borne illnesses. Therefore, it is very important to keep hot food at 60 C or higher and cold food at 5°C or lower, and check the food’s temperature at least every 4 hours during storage and distribution.

To prevent or reduce the amount of pathogens, different methods of sanitation are implemented. Sanitation is a multistep process that involves cleaning and sanitizing as two very important and separate steps. Effective cleaning and sanitation procedures, which include debris removal, use of detergent solutions, rinsing with water, disinfection where necessary and dry cleaning, are required to achieve the correct level of hygiene in food-handling or production facilities. If these are not adhered to, there is a greater risk of food becoming contaminated by pathogenic or spoilage microorganisms. There is also a risk of biofilms forming on factory and food preparation surfaces if these programs are inadequate. It is important to avoid the use of phenolic and metal-ion based products as they may cause product tainting and consumer safety issues.

Cleaning and sanitation programs include four steps:

• Routine procedures performed throughout and at the completion of food processing or preparation on a daily basis;
• Periodic procedures required less frequently;
• Monitoring to ensure the procedures are performed correctly;
• Verification to check the effectiveness of the program.

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.