back to top
This article is not yet available in the language you selected
Contamination of several foodstuffs
Article index
1. Meat
1.1 Fresh meat
A. Quantitative contamination
Slaughter
In general meat of a carcass is sterile just after slaughter. If the animal became stressed just before slaughter, the meat can be contaminated. Depending on the animal species, the number of germs can amount 103/g in that case.
During bad evisceration, bacteria can enter the intestines of the muscles and cause “bone taint” (discolouration of the meat in the neighbourhood of the bone). Via the blood stream contaminated knives can also contaminate the meat. But with good manufacturing practices during slaughter only 1 bacteria /10-100 g meat is present.
Deskinning
During deskinning contamination takes place via the skin, knives, hands, cloths, water and equipment. With GMP applied, the following counts are registrated:
Cattle : total germs : 103 – 105 /cm2
Enterobacteriaceae : 10 – 102/cm2
Sheep : total germs : 103 – 106/cm2
Enterobacteriaceae : 103/cm2
Pork : total germs : 103 – 106/cm2
Total Enterobacteriaceae is high as the skin is not removed.
Cooling
Due to rapid cooling at low temperature and high air velocity, total counts on the surface of the carcass can decrease. When the cooling occurs badly, total counts can increase; with the mesophilic count increasing more rapidly than the psychrophilic one. As pathogens are mesophilic, the risk for food intoxication will then increase. GMP requires rapid cooling under 3°C.
Cutting to pieces, deboning and packaging
During deboning and cutting to pieces, the relative surface will enlarge and the number of germs a gram will increase. The count depends on the initial contamination of the carcass, the hygienic conditions and the temperature/time conditions of the treatment. Good results are obtained at 10°C and on the conditions of efficient cleaning and disinfecting of the equipment.
B. Qualitative contamination
- Saprophytes
Gram negative rods : Acinetobacter, Moraxella, Aeromonas, Alcaligenes, Flavobacterium, Pseudomonas, Enterobacteriaceae
Gram positive rods : Corynebacterium, lactic acid bacteria, Microbacterium thermosphactum, Bacillus
Gram positive cocci : micrococci, staphylococci, faecal streptococci
Yeasts and moulds
- Pathogens
Salmonella, Escherichia coli, Yersinia enterolytica, Staphylococcus aureus, Clostridium perfringens, Clostridium botulinum
Organ meat contains higher counts than muscle meat. Its pH is higher and organs act as physiological filter.
1.2 Meat preparations
Minced meat preparations have a high microbial load due to:the meat originating from different parts of the carcass that are treated intensively and microbiological highly loaded
Mincing enlarging the relative surface and the number of germs a gram
The equipment is contaminated
Some of the spices used are microbiological highly loaded
The intestines
2. Poultry meat
A. Quantitative contamination
Transport and stunning
During transport of poultry, cages, feathers and legs are contaminated with Acinetobacter-Moraxella, Pseudomonas, corynebacterium, Micrococcus, Staphylococcus, flavobacterium and yeasts. Typical is the faecal contamination during electrical stunning (contraction of the cloaca with faeces contaminating the carcass).
Scalding
During scalding the poultry is submersed in hot water during 2-3 minutes at 60-63°C. Scalding is needed to defeather the poultry. The hot water contains 50000 germs/ml. During the heating process the mesophilic count on the carcass decreases from 107/cm2 to 104/cm2, and the psychrotrophic count decreases from 104/cm2 to 102/cm2.
Defeathering
During defeathering the total count increases. Especially in the feather follicles there is an accumulation of micro-organisms. The mesophilic number increases from 104 to 105/cm2. The psychrophilic count remains constant. During defeathering, contamination with Salmonella is critical.
Evisceration
During good evisceration, no quantitative increase of the microbial load may occur. Qualitatively, contamination with Enterobacteriaceae may occur. There is risk for cross contamination between man and equipment.
Rinsing
Rinsing occurs by spraying with water that contains 40-60 ppm chlorine. Water contaminated with Pseudomonas is a disadvantage for the microbiological quality of the poultry. By rinsing, 50 to 90% of the germs is mechanical removed.
Cooling
Cooling of the poultry carcass can in several ways:
in static tanks (1/3 ice, 1/3 water, 1/3 carcasses) during 4-24 hours : the psychrophilic count increases and there is cross contamination with salmonella
by continuous immersion in cooled water (with or counter stream, during < 1 h at 4°C : total count remains constant, but there is cross contamination with salmonella
by air cooling : light drying of the skin : total number remains constant
Weighing and packaging
Total count is determined by GMP. Cross contamination with Salmonella remains risky.
B. Qualitative contamination
At the end of the slaughter process, the microbiological contamination is as follows:the meat is sterile
on the skin there are 104 – 105 total germs per cm2, with the following species:
Pseudomonas, Acinetobacter-Moraxella, corynebacteria, micrococci and enterobacteriaceae.
Pathogenic germs: Salmonella, Campylobacter, Yersinia enterolytica, Staphylococcus aureus, Clostridium perfringens and Escherichia coli.
3. Fish, crustaceans and molluscs
A. Quantitative contamination
a. Fresh fish
Fish meat is sterile. Skin, gills and intestines are contaminated:
| Environment | Skin | Gills | Intestines |
| Pure cold water | 102/cm2 | 103/g | 103/g |
| Polluted tropical and subtropical water | 107/cm2 | 109/g | 109/g |
Additional contamination on board and land is determined by the GMP. Contamination occurs mainly via boat room, equipment, ice and man.
Treatments aboard increasing the contamination: gutting, rinsing (with sea water), storage in ice. On land, contamination occurs as follow: unloading, deboning, gutting, cutting into pieces, packaging and transport.
b. Crustaceans
Crustaceans in cold water contain 105 germs/g. In warn water, they contain 105-106 germs/g.
c. Molluscs
Oysters and molluscs contain 104 to 106 germs/g.
B. Qualitative contamination
a. Fresh fish
Fresh fish from cold water is mainly contaminated with psychrophilic Gram negative germs like Pseudomonas, Acinetobacter-Moraxella, Flavobacterium and Alcaligenes. Fish from warm water is contaminated with Gram-positive germs like Corynebacterium, Bacillus, Micrococcus. Storage in ice gives more than 90% Pseudomonas spp.
Fish from polluted zones or treated unhygienically can be contaminated with Salmonella, Enterococci, Staphylococcus aureus, Clostridium botulinum type E. In living fish, 2 pathogens can survive : Clostridium botulinum type E and Vibrio paraheamolyticus (in warm water).
b. Crustaceans
Crustaceans from cold water are contaminated with Pseudomonas, Acinetobacter-Moraxella and Flavobacterium (Gram-negative psychrophilic bacteria). Crustaceans from warm water are contaminated with Gram-positive corynebacteria and micrococci. The pathogens observed in Crustaceans are the same like those observed in fish.
c. Molluscs
In Molluscs, no to little Gram-negative germs are present. The following Gram-negative germs are found : Vibrio, Pseudomonas, Acinetobacter-Moraxella, Flavobacterium and Cytophaga.
Molluscs cultivated in estuaries that are highly contaminated, can be contaminated with enteropathogens originating from manure. Typical are Salmonella, Shigella, Vibrio cholerae, Escherichia coli, Clostridium botulinum, Clostridium perfringens, Staphylococcus aureus and some viruses.
4. Milk
Fresh raw milk can be contaminated via the udder, the exterior animal body, the equipment and other sources. The contamination can be quantitative and qualitative different.a. Udder
Residues of milk in the mamilla of animals can give rise to streptococci and micrococci. They can enter the udder and contaminate fresh raw milk with 102-103 germs a ml. When mastitis occurs, 106 germs a ml milk can be present.
In milk given by healthy cows, the following micro-organisms can be found:
- small numbers of mastitis streptococci : Streptococcus agalactiae, Steptococcus dysgalactiae, streptoccus uberis
- high amounts of micrococci : micrococcus spp. (105/ml) especially due to unsatisfactory cleaning of the milk equipment.
b. Exterior animal body
Animals are attached with ground, feed, straw and manure. The udder and milk become contaminated with Bacillus, Clostridia and Enterobacteriaceae. The contamination amounts 102 to 103/ml, depending on the cleaning and decontamination of the udder before milking.
c. Equipment
Milk machinery, cooling tanks and transport carriers can be contaminated with milk residues due to bad cleaning and disinfection. Raw milk can via this source be contaminated with S. lactis, S. cremoris, S. lactis var. diacetylactis, coliforms and gram-negative psychrophilic bacteria (Pseudomonas, Alcaligenes, Flavobacterium, Chromobacterium).
In milkstone, resistant and slowly growing micrococci, enterococci and lactobacilli can be present (105/ml milk).
d. Other sources
During milking with the hands, air contamination with micrococci and spores of Bacillus and Clostridium occurs. These spores are heat resistant and are difficult to eliminate by pasteurisation.
5. Legumes
Legumes are contaminated via the ground, water, air, insects and rodents. The contamination degree depends on the structure of the plant. Man increases the degree of contamination during harvesting. Legumes undergo destruction : (a) nutrients liberated from the legumes promote the growth of the micro-organisms and (b) invasion of micro-organisms in internal tissues takes place. During manipulation, in e.g. the rinsing of the legumes, the total number of micro-organisms will decrease. During cutting, the number of micro-organisms will increase. Insecticides will decrease the total count.The internal tissue of fresh intact legumes is spoiled with gram-negative rods.
A. Quantitative contamination
Legumes are contaminated with high amounts of bacteria.Via ground and air relative high amounts of mould spores (< 103 – 105 spores/g) can be found.
| species | degree of contamination |
| Carrots | 105/g |
| Beet | 106/g |
| Cabbage | 103/g-106/g |
| Bean | 103/g-105/g |
| Potato | 105/g-107/g |
| Peas | 105/g-107/g |
| Spinage | 106/g-107/g |
B. Qualitative contamination
a. Saprophyts
- Bacteria : Pseudomonas, coliforms, corynebacteria, lactic acid bacteria, micrococci, sporeformers- Moulds : Aerobasidium, Fusarium and Alternaria
b. Pathogens
Legumes can be contaminated by contact with manure : Salmonella, Shigella, Vibrio cholerae, Bacillus cereus, hepatitis-viruses6. Fruit
The sources of contamination of fruit are the same as with legumes. Contamination mainly occurs during transport and ripening. Damage during harvesting can give rise to invasion of micro-organisms in low contaminated fruit flesh. The main source of contamination is the water used during washing, rinsing, cooling and transport of fruit. This water is recycled, making the degree of contamination larger.A. Quantative contamination
On and in fruit, little bacteria are present. Moulds are the most important micro-organisms in fruit (103 – 105/g).B. Qualitative contamination
a. Saprophytic micro-organisms
Penicillium, Alternaria, Rhizopus, Fusarium, Mucor, and Botrytis.b. Pathogenic micro-organisms
Penicillium expansum producing patulin.7. Nuts
Nuts have a natural protection against micro-organisms. The mesocarp (coconut, walnut) and shell offer good protection against microbial contamination.a. peanuts
Peanuts can be contaminated with Aspergillus, Penicillium, Fusarium and aflatoxin producing Aspergillus flavus.
b. Tree nuts
Nuts from tree are normally sterile. However, damage during treatment, by birds, and by insects can contaminate the nut. During harvesting, the nuts can fall on the ground making them contaminated. Moisture is an aid in contamination. Faecal contamination can occur when the ground is manured.
1. Saprophytic micro-organisms
Bacteria : Pseudomonas, Acinetobacter-Moraxella, Xanthomonas, Clostridium, Bacillus, Corynebacterium, Micrococcus2. Pathogenic micro-organisms
Moulds : Penicillium, Aspergillus, Trichotecium.
Salmonella and mycotoxin producing moulds like Aspergillus flavus.
8. Eggs
The content of an egg is normally sterile. However, contamination can occur via the oviduct in ducks.Important sources of contamination of the egg shell are: intestines, nest, (faecals), dust, ground, feed, transport and man.
A. Quantitative contamination
The egg shell contains 102 – 107 germs / shell.B. Qualitative contamination
a. Gram positive cocci : micrococci, staphylococcib. Gram positive rods : Arthrobacter, Bacillus
c. Gram negative rods : Pseudomonas, Acinetobacter – Moraxella, Alcaligenes, Escherichia, Enterobacter, Aeromonas
companias