To minimize food safety risks associated with microbial pathogens, fruits
and vegetables that have visible soil or organic matter residues on their
surface should be thoroughly washed before sale. Washing should be done
with potable water only. Washing with potable water is a simple way to
reduce microbial populations on the surface of fresh fruits and vegetables.
Repeated rinsing or multiple washes may be needed to thoroughly clean produce.
If potable water is not available, wash water should be chlorinated.
Removal of soil and organic debris prior to washing in chlorinated water
(by brushing or pre-washing) is essential because organic matter reacts
with chlorine in solution to lower its effective concentration. The more
organic matter in solution, the more chlorine is tied up.
The purpose of chlorination is to drastically reduce the number of microorganisms
in the water and thus reduce or prevent inoculation with post-harvest diseases
or contamination with human pathogens. To do this, chlorine must be in
all water that contacts the produce prior to it being packed or sold. Chlorine
should also be used in cleanup water to sanitize packing equipment, picking
containers, and other sites that come in direct contact with the produce.
Chlorine gas, sodium hypochlorite (household bleach), and calcium hypochlorite
(chlorinated lime) are the most common disinfectants containing chlorine
in general use. All these chlorine containing chemicals form the same active
ingredient, hypochlorous acid, when added to water. The disinfectant activity
of a chlorine solution is determined by its pH. The pH level should be
maintained between 6.0 and 7.0 to provide for greatest effectiveness without
damage to produce and equipment. At a higher pH, chlorine is not a very
effective germicide. At a lower pH, the solution becomes corrosive to metals.
If the pH is decreased below 4.0, deadly chlorine gas is formed. Thus,
the pH of the wash water should be checked periodically. This may be done
with litmus paper (which changes color at different pH's), available test
kits, or pH meters. The pH can be adjusted to a desired level by adding
a weak acid or base, as is done in swimming pools.
It is essential that the concentration of active chlorine in the fruit
or vegetable wash water be monitored so that an adequate level can be maintained.
This may be done continuously with automatic equipment, or it may be done
intermittently with commercial chlorine test kits. Avoid kits used to check
chlorine in swimming pools since these are designed for low levels, between
2 to 6 ppm. The most effective treatment results when chlorine is metered
into the wash water continuously, whereas the most ineffective method is
to dump some in the tank occasionally. In the later case, the chlorine
concentration can vary tremendously, and during rush periods when the need
for chlorine is most critical, the tendency is to forget it. Although 50
ppm of chlorine is probably more than adequate if that concentration is
maintained, the general recommendation is for 100 to 150 ppm. Higher concentrations
provide some protection against unusual conditions resulting from overloading
the systems or from loads containing excessive amount of organic matter.
To make an effective sanitizing agent containing approximately 70 ppm
chlorine for use on fresh produce, food handling equipment and machinery
add one pint of household bleach (5.25% sodium hypochlorite) to 50 gallons
of water. Adding 2 pints of 40 grain distilled white vinegar should adjust
the solution's pH to between 6 and 7. Adding 1/4 pint wetting agent, such
as liquid soap, will help the chlorine get into the nooks and crannies
on the surface of produce.
The National Organic Standard at first blush apeared to limit the use
of chlorine to 4 ppm where it comes into contact with produce on organic
farms. However, recent interpretations of the organic standards by the
National Organic Program appear to allow chlorine in wash water at levels
higher than 4 mg/L,sufficient to control microbial contaminants.
But, while chlorine use in water cycle on an organic operation is not limited
to 4 mg/L, the discharge from that system may not exceed 4 mg/L, so dilution
will likely be required. Further, organic certification agencies may differ
in their interpretation of the NOP ruling, so be sure to check with your
certifier before adding chlorine to wash water.
Chlorine is highly poisonous and must be handled with care according
to instructions. For the safety and comfort of the workers, provisions
must be made for adequate ventilation to remove chlorine fumes from enclosed
packinghouses. All workers handling chlorine and chlorine equipment should
use protective equipment recommended for the particular form that is being
used. Read the label before opening any container.
- Coon, S. "Chlorination Cuts Postharvest Losses." American Vegetable
Grower, Sept. 1990.
- Hicks, J.R. and R.H. Segall. "Water Chlorination for Vegetable Packinghouses".
VC-1, University of Florida Cooperative Extension, Gainsville, FL.
- Schlimme, D. "Cleaning and Sanitizing Fresh Produce and Fresh Produce
Handling Equipment, Utensils and Sales Areas". Fact Sheet 715. University
of Maryland Cooperative Extension, College Park, MD.
- Suslow, T. "Microbial Food Safety is Your Responsibility!". Dept. of
Vegetable Crops, University of California, Davis, ucanr.org/sites/GAP/newsletters/Microbial_Food_Safety_IS_Your_Responsibility41362.PDF.