In this section:
Sanitation
Significant efforts have been made to assist growers, packers and exporters to identify potential hazards.
Water quality is recognised as a primary source of contamination (Anon, 1998). Whenever water comes in contact with produce, its quality dictates the potential for contamination. This applies equally for agricultural water and processing water. Water sanitation can play a critical role in processing plants by reducing contamination of fresh fruit and vegetables. This paper describes sanitation practices used by citrus packers to illustrate the role of sanitisers in food safety.
More information: Peter Taverner or Nancy Cunningham
Application to citrus packingsheds
Fresh produce has populations of 104 to 106 microbes per gm when they arrive at packingsheds (Beuchat, 1995). Water used during postharvest handling can clean contaminated dirt from produce but it may also be a source of contamination. Wash water is often recirculated, which can lead to a build-up of microbes, including pathogens. Fruit is sprayed with recirculating fungicide solutions to control postharvest diseases. These chemicals are specific and do not control other pathogens that, if present, pose a health risk
Sanitisers can maintain water quality by reducing microbe levels in water. Successful maintenance of processing water requires an understanding of the sanitisers used and the factors likely to affect their performance in packingshed operations.
Classes of sanitisers
The sanitisers used in the citrus industry are chlorine-releasing compounds. Sanitisers commonly used are listed:
- Hypochlorites are inexpensive and widely used. However, they must be monitored carefully as they are very sensitive to pH, are rapidly inactivated by organic matter and corrosive to metal. They are sold as a concentrated liquid (sodium hypochlorite) or in a granular/ powdered form (calcium hypochlorite).
- Isocyanuric acid derivatives release chlorine more slowly. They are often formulated with detergents, surfactants and buffers to improve cleaning and wetting.
- Bromo-chloro-dimethyl-hydantoins rely on a synergistic effect between chlorine and bromine to produce greater fungicidal activity.
- Chlorine dioxide is a powerful oxidising agent. Low levels are required, it is more stable in the presence of organic matter and is effective at a wide pH range. There are several methods and products used to generate chlorine dioxide.
- Peroxyacetic acid is a relatively new sanitiser it is strongly oxidising with a strong "vinegar" odour with high microbial activity. Works best at pH 5.5-8.2
- Iodine works at a wider pH than chlorine and is effective at pH above 8. Less corrosive than chlorine.
Factors affecting ability of Chlorine sanitising products and the factors affecting their respective activity have been reviewed (Taverner, 1998; Suslow, 1997). The major factors are listed:
pH - Many sanitation compounds are very pH sensitive. The activity against microbes is related to the amount of undissociated hypochlorous acid (HOCl) (see Table 1).
Table 1: The % undissociated hypochlorous acid at different pH (O'Grady, 1979)
| pH | % hypochlorous acid |
|---|---|
| 3 | 99.7 |
| 6 | 96.9 |
| 7 | 75.7 |
| 8 | 28.3 |
| 9 | 3.0 |
Concentration - The influence of concentration on kill is relatively minor compared to pH and time. Often a 4 fold increase in concentration results in only a 50% reduction in killing time. However, concentration may influence corrosion rates greatly.
Temperature - Every 10oC increase in temperature reduced killing time by up to 60%. This result will depend on the product. High temperature may increase the risk of corrosion.
Organic Matter - The main disadvantage of many chlorine compounds are that they are rapidly inactivated by organic matter. This creates a huge chlorine demand in dirty situations and makes surface disinfection of oranges very difficult.
Water Hardness - Calcium and magnesium levels of up to 400ppm have little effect on the activity of hypochlorites (Rudolph & Lavine, 1941). These compounds are reasonably tolerant of water hardness.
Compatibility with Other Chemicals - Chlorine can be inactivated when in contact with surfactants and other compounds. This can lead to incompatibility with postharvest fungicides (Taverner, 1998).
Take home message
Whenever water comes in contact with produce its quality dictates the potential for contamination. Sanitisers can play an important role in controlling water quality but only with a clear understanding of their strengths and limitations.
References
Anon (1998). 'Guide to minimise microbial food safety hazards for fresh fruit and vegetables.' (Food safety initiative staff, HFS-32, USDA, 200 C Street S.W. Washington, DC).
Beuchat L.R. (1995) Pathogens organisms associated with fresh produce. J. Food Prot.. 59: 204-216.
O’Grady G.F.G. (1979) A review of chemical sanitisers and disinfectants for winery use. Winemaker and grape grower.
Rudolph A.S. and Lavine M. (1941) Factors effecting the germicidal efficiency of hypochlorite solutions. Bull 150. Engr. Exp. St., Iowa State College.
Suslow T. (1997) Postharvest Chlorination. DANR UCLA. Copies from http://danrcs.ucdavis.edu.
Cunningham N.M (2007) Packer Newsletter. 86 (PDF)
