Fresh Produce – Prevention of Microbial Contamination

Most people believe that if fruit and vegetables were properly washed, then there is little health risk. It is a common believe that freshness of fruit and vegetables could be easily detected via look, smell, texture, colour, best before date on packaging and many deduced that one would be unlikely to eat a fruit or vegetable if it has gone “bad”. Most consumers are not aware of the risks of Salmonella, E.coli, etc. when it came to the fruit and vegetables category. These risks are normally linked with poultry and meat products only.

There are many points during production of fruits and vegetables at which microbiological contamination can occur. These include:

  • Growing (seeds, soil, water, manure, insects, animals)
  • Harvesting (faeces, handling, equipment, transport)
  • Post-harvest handling (washing, packing, vehicles, cross-contamination)

Fruit and vegetables (also termed ‘fresh produce’) are increasingly being recognised as an emerging vehicle for foodborne illness in humans. Traditionally meat, milk and egg products were the ‘usual suspects’. The consumption of fresh produce has now been linked, both epidemiologically and microbiologically to infectious intestinal disease.

Fresh produce foods typically have fewer barriers to microbial growth such as preservatives; therefore, simple errors can make the food unsafe. Cross-contamination is understandably a major contributing factor in outbreaks involving fresh produce as these foods are usually eaten raw.

Pathogens transmitted via fruit and vegetables

Bacterial:

  • Aeromonas
  • Bacillus cereus
  • Campylobacter
  • Clostridium botulinum
  • Clostridium perfringens
  • Escherichia coli O157
  • Listeria monocytogenes
  • Salmonella
  • Shigella
  • Staphylococcus aureus
  • Vibrio cholerae

Viral:

  • Hepatitis A
  • Norovirus

Protozoan:

  • Cryptosporidium parvum
  • Cyclospora cayetanesis
  • Giardia

Preventing Microbial Contamination along the Food Chain

There are a number of sources of contamination, all of which must be controlled in order to prevent or minimise microbial contamination of fresh produce. The key areas where microbial contamination can occur are in the field;during harvesting and processing; and in the home.

All efforts should be taken to harvest fresh produce that is of the highest microbiological quality possible. Preventing cross-contamination during harvesting can be achieved via thorough cleaning and decontamination of equipment, containers and transport vehicles. An effective decontamination stage is essential prior to packaging to help reduce the level of pathogenic and spoilage organisms in Ready-to-Eat produce.

Strategies used to control harmful bacteria:

  1. organic acid rinse: lactic, acetic & propionic
  2. ozonation
  3. chlorinated water wash
  4. hydrogen peroxide
  5. combinations of acid and hydrogen peroxide (peroxyacetic acid)‏
  6. acidified sodium chlorite (ASC)
  7. storage temperature after anti-microbial treatment

How effective are the decontamination strategies?

One study conducted in 2003 tested 13 disinfectants on strawberries. Of all the products tested, sodium chlorite acidified with citric acid (ASC) was the most effective. (Food Protection Trends, November 2003, pp. 882 – 886).

Acidified Sodium Chlorite (ASC) solutions is approved by FDA (21CFR173.325 (e)) to be used as an antimicrobial agent on raw agricultural commodities in the preparing, packing, or holding of the food for commercial purposes. It may be applied as a dip or a spray. Treatment of the raw agricultural commodities with acidified sodium chlorite solutions shall be followed by a potable water rinse, or by blanching, cooking, or canning.

Acidified Sodium Chlorite (ASC) solutions is also approved by FDA (21CFR173.325 (g)) to be used as an antimicrobial agent in the water applied to processed fruits and processed root, tuber, bulb, legume, fruiting (i.e., eggplant, groundcherry, pepino, pepper, tomatillo, and tomato), and cucurbit vegetables as a component of a spray or dip solution, provided that such application be followed by a potable water rinse and a 24-hour holding period prior to consumption. However, for processed leafy vegetables (i.e., vegetables other than root, tuber, bulb, legume, fruiting, and cucurbit vegetables) and vegetables in the Brassica [Cole] family, application must be by dip treatment only, and must be preceded by a potable water rinse and followed by a potable water rinse and a 24-hour holding period prior to consumption.

However, heating remains the most effective technique used to control pathogenic microbial growth. Heating of all fruits and vegetables is not possible due to the negative effects on some products. However, it is possible to use heat on some products. In one study, hot water treatment of Cantaloupe with 158 deg. F. water was able to achieve a 2-log reduction of Salmonella and treatment with 206 deg. F. water achieved 3.4-log reduction of Salmonella (Journal of Food Protection, Vol. 67, No. 3, 2004, pp. 432-437).

New technologies are continuously being explored to reduce foodborne pathogens in fresh produce. These include:

  • High pressure processing
  • Dense phase carbon dioxide processing
  • Ultra-violet irradiation processing
  • Electron-beam irradiation processing

Reference:

Consumer Focused Review of the Fruit and Vegetable Food Chain, February 2007 (Safefood)

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