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Initial Contamination of Fresh Foods |
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Initial Contamination of Fresh Foods - Foods consumed by man and animals may be classified into eight main divisions. These are cereal and cereal products, vegetables, fruits, milk and dairy products, meat and poultry, eggs, sea food, and sugar and sugar products. Broadly, these may be considered as plant products and animal products.
Foods may also be classified on the basis of stability :
1. Perishable foods such as meat and fish.
2. Semiperishable foods such as potatoes.
3. Stable foods such as cereals, flour and sugar.
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Any stable or semistable food becomes perishable food under moist condition.
Plant products:
The internal tissue of whole, healthy plants and fruits are usually free from microorganisms. However, the external surfaces of plant products arc contaminated by microorganisms from the soil, air, insects, human handlers, and packages. Cereals, so long as they are dry, can be preserved for a considerable time, if free from insects.
Sugar products are low in moisture content and possess a hip osmotic pressure, generally adequate to prevent microbial growth.
Honey, syrups, etc., are relatively stable, but when diluted with an equal volume of water decompose easily.
Root crops such as potatoes, beets, and carrots are coated with soil microorganisms. But these vegetables possess an exceptionally impenetrable skin and are non-succulent.
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They are rather stable, unless they are spoilt and the cells damaged. Low growing leafy vegetables such as lettuce, spinach, and cabbage are also heavily contaminated.
These products have a softer surface and are easily invaded by microorganisms. Fruits that grow some distance above the ground are contaminated by insects and by microorganisms in air. The latter are principally soil organisms. Fruits are rather high in sugars and usually somewhat acid. Hence; decomposition is likely to be by yeasts, as in grapes, or by moulds, as in citrus fruits.
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Animal products:
Animal products are subject to intrinsic as well as environmental and human contamination. The internal portions of a piece of meat are usually free from microorganisms if a healthy animal is properly slaughtered, as in an abattoir by a blow on the head, or by cutting the jugular vein. Meat immediately gets contaminated with microorganisms upon exposure in the abattoir.
The organisms are derived from hides, hair, and intestines of the animals, gloves, hands, and butchering instruments, and the air of the slaughter house. Freshly dressed eviscerated poultry have a microbial flora on their surface. Organisms arc normally present on the live birds, and the manipulations during killing, defeathering, and evisceration introduce organisms on the surface. The microbial flora of freshly caught fish reflects the microbial quality of the water from where they are harvested. Oysters, mussels, and some other shellfish fatten on sewage.
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This seafood is potentially capable of transmitting various pathogenic microorganisms. When the fish are cleaned and cut on shipboard under poor handling conditions, they are more likely to be covered by microorganisms, e. g., fish fillets clean, uncracked fresh eggs are usually free from microorganisms with the shell.
The interior of the egg gets contaminated under poor conditions of storage. The shell may be soiled with blood, manures, feathers, nest material or broken eggs.
These substances are most likely contaminated with organisms which are drawn in along with the air through the shell pores as the egg cools.
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