Without bacteria in dairy production, products like cheese and yoghurt would not exist. However, for safe food production it is critical that only the right bacteria are allowed to grow and thrive, and that harmful pathogenic bacteria are eliminated from the production and processing.
Bacteria in Milk
Bacteria in dairy production begins with the milk. When milk is first secreted it is sterile, but by the time it leaves the udder it has already been contaminated with bacteria. Most of these bacteria are harmless and the numbers are low. Throughout the milking, handling, storage and processing it is possible for further bacteria to be introduced into the milk. If these bacteria in the milk are allowed to multiply they can cause the milk to spoil and be unsuitable for consumption.
Why is it significant?
Information about the bacteria in milk can be used to assess its sanitary quality and the production conditions. Reputable suppliers are likely to have lower bacterial loads in the milk as a result of more stringent quality controls and checks. The milk can also be further contaminated throughout production with pathogenic bacteria which may cause food poisoning. Production controls should help to minimise bacterial growth or destroy harmful bacteria to help keep the food safe for consumption.
Spoilage and Pathogenic Bacteria
The process of food deteriorating to a point that it would be unappetising or unsuitable for human consumption is called spoilage. It may be that the texture, colour, odour or flavour have changed due to microbial activity. These microbes, or the enzymes that they produce can degrade the proteins, carbohydrates or fats that make up the food. In milk, most of the bacteria that would cause spoilage are destroyed by pasteurisation temperatures, although some are heat stable and can survive the pasteurisation process.
Pathogenic bacteria are bacteria that will make you ill if ingested, often described as food poisoning. In hygienic dairy production, the threat of serious illness such as tuberculosis, brucellosis, or typhoid fever are now very low. This is largely due to improvements in food laws including regulating of pasteurisation, where milk is heated to a high temperature then cooled rapidly to kill bacteria. Food borne illness as a result of bacteria in dairy production is now most often associated with milk that has not been properly pasteurised, or with products that have been contaminated post-pasteurisation during processing, storage or transport.
In the UK it is still possible to buy raw or unpasteurised milk, and businesses that sell it have to comply with additional controls to ensure that bacterial levels are low. However the Food Standards Agency does recommend that people in vulnerable groups such as pregnant women, the elderly, the immune compromised, infants and children should not consume unpasteurised milk and that packaging must include a warning about the risk of food poisoning to allow customers to make informed decisions before consumption.
Producing Cheese and Yoghurt
Some desirable bacteria in dairy production initiate chemical changes in the milk which are essential to the production of products such as cheese and yoghurt. These may be added to pasteurised milk in the form of a starter culture. Starter cultures are the desirable bacteria added to milk, which are used in the production of cultured or fermented dairy products like cheese and yoghurt. They replace the natural microorganisms in the milk which may have been destroyed in pasteurisation or are too inefficient or unpredictable. The subsequent predictable bacterial growth provides controllable characteristics in the finished dairy product.
Starter cultures may have a range of functions including altering the flavour or aroma, and inhibiting the growth of undesirable organisms. Today, most starter cultures are laboratory produced by scientists and so produce very predictable results. The starters may contain only one type of bacteria (known as simple or defined starters) or might combine two or more bacterial strains each with their own characteristics (known as mixed or compound starters).
How do the bacteria in cheese and yoghurt work?
Many starters contain some form of lactic acid bacteria which ferment lactose into lactic acid. The acid causes the proteins in the milk to precipitate or clump together which is why the fermented product is usually a thicker consistency than the milk. The high acidity generated by these bacteria inhibit the growth of other bacteria which enables them to outcompete any pathogenic or unwanted bacteria still remaining.
Yoghurt production usually uses two bacterial species, Lactobacillus bulgaricus and Streptococcus thermophilus. Once the yoghurt has the right flavour and consistency, it is usually kept chilled, slowing the bacterial growth and preventing further fermentation. Cheese production is similar, but the solids are usually separated from the whey (the liquid that remains) and processed further using enzymes such as rennet. In some cheeses, other bacteria or moulds may be added such as Penicillium mould in blue cheese.
Probiotics and Health benefits
Some yoghurts and dairy products make claims about “probiotics” which are live microorganisms which have supposed health benefits for the host if there is a sufficiently high concentration. While research is ongoing, there is not currently enough evidence to point to a definitive cause and effect for their beneficial claims.
So are the bacteria in dairy production safe to eat? If the manufacturer has followed safe food production protocols there is no reason to be concerned. The bacteria introduced are considered to be safe for consumption, and some like the veins in blue cheese are intentionally added for their flavour or other characteristics. Any harmful pathogenic bacteria should only exist in small enough numbers that they should not make you ill.
If you found this article useful, you may wish try iQualifi’s online level 2 course in Food Manufacturing to learn more about bacterial controls in food manufacturing. Or you may be interested to learn about how producers of liquid products like dairies keep their pipework clean and bacteria free with our blog.