Intoxicating substances in milk present a very big challenge when dealing with food poisoning incidences.
Given that milk is a complete food with a stable proportion of both macronutrients and micronutrients, it is an ideal vehicle for the pathogens that produce toxins.
Food toxicology is the study of these toxins an their effects.
Food poisoning: infectious organisms or their toxins can contaminate food during production/processing. Click To Tweet
The toxic compounds can originate from:
- Natural sources as metabolites of plants and animal metabolism
- Biological or chemical contaminants from the air/water/soil
- Intentionally introduced food additives
- Toxicants from the food processing e.g. acrylamines
Sources of food poisoning in milk:
Microorganisms and their toxins
Milk and milk products harbor microorganisms that metabolize the milk for their normal metabolic needs producing metabolites in the process.
These metabolites/byproducts can produce both desirable and undesirable effects in the product.
Desirable effects include flavouring and texture while undesirable effects may include food poisoning.
Sources of microorganism contamination include the following:
Dairy animal: – health of the animal is an important consideration because the animal can transmit the diseases to humans through the milk e.g. brucellosis. They can get into the milk directly from the udder or indirectly through body discharges.
Human handlers: – sick people can transmit diseases like TB and brucellosis to other humans through the milk.
Environment: – the general cleanliness of the cowshed and the milking parlour has a greater bearing on the quality of the milk produced from the farm.
Antibiotics: – the residues of the antibiotics that remain after treating the cow for mastitis or any other bacterial infection.
These residues will find their way into the milk and cause contamination or even food poisoning.
These contaminants include the following:
Insecticides: – such as those used on the cowshed to control ectoparasites, which the animal may partially absorb through the skin and release into the milk later.
Foods containing organophosphate pesticides can cause food poisoning by inhibiting the acetylcholinesterase enzyme.
Preservatives and disinfectants: – added to increase the storage time of the milk e.g. hydrogen peroxide, boric acid, and formalin.
Formalin and boric acid are highly toxic in small quantities. Some compounds such as the hypochlorites remain in the milk containers after cleaning.
Radionuclides and heavy metals
Radionuclides including iodine 131 and Strontium 90 may be present in contaminated milk. Iodine 131 causes malfunction of the thyroid gland while Strontium 90 is lodged in the bones.
Heavy metals such as Zinc, Copper, and Iron gets into the milk through corroded metals.
Heavy metals such as Zinc, Copper, and Iron gets into the milk through corroded metals. Click To Tweet
Serious food poisoning by these metals is rare due to their effect on colour and taste; one will easily identify them due to their offensive smell and taste and therefore, choose not to drink the milk.
Relatively large amount of heavy metals are required to cause toxicity. However, these metals have a cumulative effect in the body and their effect will multiply over time.
This type of contamination is prevalent during dry season when animals eat a lot of plant matter. There is no significant evidence to show that toxic compounds are present in milk in quantities enough to cause effect on human consumers.
Flavor and drugs excreted in milk
Flavours act as extraneous substances that occur when cows consume certain plants that impart flavor in milk rendering the milk unwholesome.
A number of therapeutic drugs might be excreted in milk in minute quantities. This might affect heavy consumers of milk, especially children whose immunity is yet to be fully developed.
Do not use the milk for at least 96 hours after the last administration of drugs.
Dirt and other abnormal bacterial load.
The common adulteration methods include watering and skimming or addition of foreign fat.
To determine the amount of dirt present in a given batch of milk, sample half a liter of the milk, warm and pass through filter paper.
Compare the dirt on the filter paper with a sediment comparison chart. Warming makes the milk fat liquid to allow it to pass through the filter paper.
To test for foreign fat in any given milk sample, extract the fat using Rose Gotlieb method and then use a Butrorefractor at 40°C to take the readings.
The difference in reading from the standard value will show the presence of foreign fat. The readings of the Butrorefractor range from 1 – 100.
The normal refractive index of milk ranges between 1.422 and 1.895.
Test for foreign fat in milk via Rose Gotlieb method; read the buterorefractor at 40°C Click To Tweet
You can also employ the Gas-Liquid Chromatography (GLC) method to check the fatty acids present in the milk sample.