Sanitisers and fungicides

There are few or no postharvest fungicides available for vegetable producers. A number of sanitisers can be used which help control pathogens in water and on vegetable surfaces. It is essential to include sanitisers in recirculating water systems. 

The ideal postharvest fungicide is water soluble, effective against a wide range of spoilage organisms, has no negative effect on the vegetable, is safe to workers and consumers, remains active over a long period, leaves no visible residues and is cheap. Unfortunately, no such product currently exists!

For many years, chemical fungicides were the main method used to control postharvest fungal diseases, particularly for fruit crops. However, a search of registered fungicides for postharvest application to vegetables reveals only one chemical registered for bulb crops, and two chemicals registered for potatoes. The remaining ‘fungicides’ are products usually considered sanitisers, but which have broad fungicidal activity. 

Unlike chemical fungicides, not all sanitisers need to be registered for use on vegetables.

  • Sanitisers used to ensure food safety by sanitising water or equipment DO NOT need to be registered.
  • Sanitisers marketed or supplied specifically for controlling spoilage organisms DO need to be registered.

If wash water is being recycled, or dip-tanks are being used, then it is essential to include a sanitiser to prevent spread of fungi and bacteria in the water during packing processes.

Sanitisers can also help kill fungi and bacteria on the surface of the produce. They will not affect pathogens that are already inside the vegetable flesh or internal air spaces.

There are a number of sanitisers that can be added to water or air, including:

  • Chlorine based compounds—calcium hypochlorite, sodium hypochlorite, bromo-chloro compounds, chlorine dioxide
  • Peroxyacetic acid
  • Iodine
  • Ozone 

Chlorine compounds  

Chlorine is cheap and effective. However, effectiveness depends on pH, and chlorine can be rapidly deactivated in dirty water. Chlorine is not permitted by some markets. 

The most common sanitiser used is chlorine. Chlorine is cheap, effective and easy to use. A number of chlorine-based compounds are available. The two main ones are calcium and sodium hypochlorite.

  • Calcium hypochlorite is a powder or granule, and is a common active ingredient in swimming pool chlorine products.
  • Sodium hypochlorite is a liquid and the active ingredient in household bleach.

Mixed with water, calcium and sodium hypochlorite generate hypochlorous acid (HOCl). This is the active form of chlorine that oxidises spores and bacteria in the water.

However, formation of HOCl is a function of pH. At high pH, the amount of HOCl decreases, with most chlorine in the inactive, oxidised form (OCl-). This is ineffective against pathogens.

Note that many chlorine test kits measure 'total chlorine', which is HOCl + OCl-.

The results from test kits therefore do not necessarily indicate how effective the solution is at killing microbes. This makes it important to also test pH, to check that chlorine is in the active form.

If water has pH over 7.5 it must be acidified for chlorine to be effective. Hydrochloric acid is often used to lower pH. However, this must be done carefully because if pH falls below 3 poisonous chlorine gas can be given off.

Hypochlorous acid can also be generated on site using electrolysis. The only inputs are electricity and small additions of salt (sodium chloride), or the process may use salts already in the water.

Effect of chlorine on the amount of hypochlorous acid present in the water.At high pH chlorine is in the inactive form and ineffective against microbes. At low pH poisonous chlorine gas is formed. Chlorine will only be effective against pathogens if pH of the water is 4 – 7.5. 

Chlorine is effective because it reacts with fungal spores and bacteria. However, it also reacts with other organic materials, such as dirt and debris. This means that chlorine is deactivated in dirty water. In general, double the amount of chlorine is needed to control pathogens if the water is dirty. Chlorine is corrosive to equipment, and is  deactivated by exposure to light, air and metals.

Typical doses used for sanitation are 50–200ppm of active chlorine (HOCl) in water. However, even much lower concentrations (10ppm) continue to provide some control of microbes.

Bromo-chloro-dimethyl-hydantoin (Tradename Nylate®) is less affected by organic matter than calcium or sodium hypochlorite. It is also less affected by pH, remaining active up to pH 8.5. Lower dose rates are usually needed to control pathogens, with the product usually used as a complete monitoring, filtration and dosing system. 

Chlorine dioxide gas is also less affected by pH than the hypochlorite sanitisers. It can be generated on site, is active at very low doses (1–10ppm) and is unaffected by organic matter. However, good ventilation is needed to ensure workers are unaffected, and the gas is explosive at high concentrations. 

Peryoxacetic acid 

Peryoxacetic acid is less affected by dirty water and pH than chlorine and remains effective at low temperatures. 

Peryoxacetic acid (Peracetic acid / PAA, sold under tradename Tsunami®) also remains active even when organic matter in the water is high. It is effective against a wide range of plant pathogens, and remains effective even at low temperatures, such as in a hydrocooler. High temperatures and high pH will deactivate the product. Dose rates are typically 50–150ppm. 

Note that peryoxacetic acid is not effective against yeasts, so is not suitable for use on carrots.


Iodine is an effective sanitiser and is not affected by dirty water. Australian diets are somewhat deficient in iodine, so use as a sanitiser has additional potential benefits. 

Iodine is not affected by organic material in the water and is effective at a wider pH range than chlorine. Iodine is also an essential element needed for good health; the recommended daily intake for adults is 150μg/day. However, iodine is often lacking in the Australian diet. Using iodine as a sanitiser therefore has potential benefits in addition to its wide activity against fungal spores and bacteria.

Fully automated iodine dosing and recovery systems are commercially available and used by some vegetable producers. The main issues are cost and availability. 



Ozone gas reacts with fungal spores and bacteria, but also with equipment and workers. It is difficult to monitor, yet the effect on waterborne microbes is highly dependent on contact time and concentration. There are no residual effects on washed products.

Ozone (O3) is a colourless gas with a distinctive smell. It is produced naturally during thunderstorms as well as by electronic equipment such as photocopiers.

Ozone is highly reactive with organic compounds. These include fungal spores and bacteria, and also soil, equipment, cardboard packaging and workers. Ozone is very effective at killing fungal spores in the air, with ozone generators often marketed as a way of sanitising cool rooms. While this reduces airborne pathogens, unless ozone directly contacts the surface of the vegetables it will have little effect on diseases already present. Ozone has no effect once fungi or bacteria are inside the vegetable. Ozone is also difficult to measure, can cause superficial damage to products at high concentrations and poses significant risks to worker health if not properly controlled.

Ozone can be bubbled through wash water to sanitise it. It reacts rapidly, with effectiveness dependent on contact time and the amount of ozone suspended in the water. As it reacts with soil, ozone is better suited to single use wash water than to recirculating water in dumps and flumes.

Once reacted, ozone has no residual activity. Passing water through an ozone generator will therefore kill pathogens carried in the wash water, but have no impact on microbes still on the surface of the vegetables. 

Overview of sanitisers suitable for fresh vegetables

Sold as… Monitoring Key points
Calcium hypochlorite Swimming pool chlorine
Frexus dry chlorine briquettes, Ym-Fab Activ-8
Test strips
Inexpensive and easy to use
Some residual effects on pathogens
Important to monitor and control pH (4.0 – 7.5)
Quickly rendered ineffective if water is dirty
Corrodes metals and packing equipment
Household bleach
Bromo chloro dimethyl hydrantoin (BCDMH) Nylate® Automatic
Reasonably inexpensive
Some residual effects on pathogens
Less corrosive than hypochlorites
Less affected by dirty water than
Still effective at up to pH 8.5
Reacts to form both hypochlorous acid and hypobromous acid (2 x active ingredients)
Must be generated on site
Chlorine dioxide  Vibrex hortiplus® Redox probe Effective at low concentrations
Some residual effects on pathogens
Not affected by dirty water
Still effective at up to pH 8.5
Must be generated on site
Relatively expensive
Requires good ventilation for workers
Peroxyacetic acid (PAA)  Tsunami® PAA test strips
Automated analyser
Less affected by dirty water than hypochlorites
Less affected by pH than hypochlorites
By-products are biodegradable
Effective at low temperature
De-activated by high pH or high temperature
Iodine AIS iodine granules Automated analyser Effective at broad pH range
Not affected by dirty water
May benefit human health
Only available as a dosing system
Relatively expensive
Corrosive to metals
Ozone   N/A Highly effective at killing fungal spores and bacterial pathogens
De-activated by dirty water
No residual effects on pathogens
Not easily monitored and concentrations highly variable
Corrosive to metals and equipment