Foodborne Listeria Monocytogenes in Seafood – Preventive Controls

Listeriosis, caused by Listeria monocytogenes, is a significant public-health concern as a result of its clinical severity and high mortality. Large foodborne outbreaks of listeriosis have occurred during the last two decades in Europe and the United States. L. monocytogenes has been associated with a wide variety of food especially seafood and poultry. As such it is highlyimportant that seafood manufacturers establish effective Listeria control plans in their factories.

Elements of a Complete Listeria Control Plan

  1. Sanitation and GMPs
  2. Training of Plant Personnel
  3. Plant Environmental Monitoring/Testing
  4. Raw Material Controls
  5. MinimizeGrowth in Finished Product

Various biocides and sanitation methods have been tried by the industry. Some of the sanitation methods currently being used include:

  • Liming – this is a cost effective method and is being used to treat raw whole Atlantic salmon. The salmon is soaked prior to raw processing. Chlorine dioxide is frequently used as a dip after liming and before splitting.
  • Sodium hypochlorite – this is added to the processwater and used on raw headed and gutted fish and raw fillets. This is the one of the most cost effective method.
  • Nisin-containing ingredientsystem (maltodextrin, cultured dextrose, sodium diacetate, egg white lysozyme, and nisin). This however, is a rather costly method.
  • Sodium/potassium lactate/sodium diacetate – these were tested on cold smoked salmon at brine/cure step. However, the treatment leaves a strong flavor giving a negative effect on the seafood quality
  • Citro bio – this has been tested oncold smoked fillets. Applied prior to drying and after fat line removal.
  • Lactobacillus extract spray – this proprietary chemicalhas also been tried
  • Lime or Ozone – washing raw headed andgutted fish in lime or with ozone. Somewhat effective.
  • Acidified Sodium Chlorite or Chlorine Dioxide – these has been used to wash headed and gutted fish prior to splitting. This is normally used as a fish wash dip after the liming process and before splitting the fish.

Acidified sodium chlorite solution is an FDA approved secondary direct food additives permitted in food for human consumption (21CFR173.325). The additive is allowed to be used as a single application in processing facilities as an antimicrobial agent to reduce pathogenic bacteria due to cross-contamination during the harvesting, handling, heading, evisceration, butchering, storing, holding, packing, or packaging of finfish and crustaceans; or following the filleting of finfish. The solution may be applied as a dip or spray. It is used at levels that result in a sodium chlorite concentration of 1,200 ppm, in combination with any GRAS acid at levels sufficient to achieve a pH of 2.3 to 2.9. Treated seafood shall be cooked prior to consumption.

Equipment Focussed in Sanitation Programme

  1. Slicers – Spray with chlorine dioxide at the end of the workshift. If environmental sampling shows any bacterial counts on equipment orproduct contact surfaces, the equipment is dismantled and heated at 300 F for 35min in the smoke oven. Larger pieces of equipment are shrouded andsteamed.
  2. Skinner
  3. Splitting machines
  4. Smoking racks
  5. Floor stress mats – soak inchlorine dioxide at 150 ppm without drying
  6. Drains and drain coverings – some manufacturers use iodine blocks in the drains and pluggingthe drains and soaking them with 200 ppm chlorine
  7. Tubs
  8. Food contact areas that involve complex equipment and parts that are not alwaysconstructed with sanitary parts, e.g., use of rubber or other absorbentmaterials that can be difficult or impossible to sanitize.
  9. Cart wheels, doors, smoke racks, pallet jacks, etc. – some manufacturers practice spraying these with chlorine dioxide solution during processing

Plant Environmental Monitoring

The frequency of conducting microbiological testing varies between the variousseafood manufacturing facilities. The frequency can range from 2 times per weekto 2 times per year, depending on the rate/size of operation, the level ofcontamination usually detected, the amount of historical data available, the effectiveness of the sanitation programme in place, etc. Some facilities even engage third party to verify routinely.

Minimize Growth in Finished Product

All seafood manufacturers have testing programmes in place for their finished product. However, the frequency of testing varies, ranging from every batch to 4 times per week to 4 times per year where some even engage third party testing routinely.


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