Phage contamination and phage rotation in dairy production

Disruption of the fermentation process by bacteriophages

For the production of yoghurt, cheese and other dairy products, a culture (also called starter culture) is added. Such a culture consists of lactic acid bacteria. These bacteria convert lactose into lactic acid; which lowers the pH of the milk, thus preventing the growth of other harmful bacteria. These lactic acid bacteria start to grow during fermentation. Fermentation means that something becomes sour; in this case, milk is made sour until it becomes a yoghurt, buttermilk or cheese. This fermentation process can be disrupted by bacteriophages. This is because bacteriophages destroy the desired lactic acid bacteria before they can do their ‘work’.

What exactly is a bacteriophage?

Bacteriophages (phages for short) are viruses that can attack and destroy bacteria. They are the ‘natural’ enemies of bacteria. They occur wherever there are bacteria, such as on our skin and in our intestinal system and in nature. Bacteriophages only die at temperatures above 80°C. Often in dairy preparation, including cheese making, these temperatures are not reached and so the phage can survive during the heating step of the milk.

A bacteriophage fights a bacterium by specifically attaching itself to it and introducing its hereditary material into the bacterial cell. This disrupts the bacterium and it then starts producing lots of new phages. The phage multiplies very rapidly in a bacterium. This allows the phage to spread in the area and look for new bacteria to multiply. This happens so fast that the bacteria do not multiply, but the phage does. The phage takes over and inhibits or stops acidification altogether.

6 measures to prevent phage contamination

There are several causes through which phage contamination can occur. Largely, it has to do with poor hygiene in and around the process area that allows lactic acid bacteria to be present. And it is precisely in these places that phages can start to grow. Fortunately, there are a number of measures that can be taken to prevent phage contamination.

1. Ensure proper cleaning and disinfection of equipment and surroundings.
   Good hygiene, cleaning and disinfection of equipment and surroundings (process area) should be a basic requirement at all times.
2. Give extra attention to cleaning and disinfecting tools.
   Consider brushes and other auxiliary materials. Clean and disinfect these in a separate container.
3. Replace rubber rings and hoses on time.
   These can become porous, allowing bacteria and phages to survive more easily as contamination remains.
4. Check and repair walls and floors.
   Phage contamination can also take place via airborne infections through cracks and seams in walls or floors. This is often slow and will not immediately lead to outbreaks, but can cause problems over time.
5. Wash work clothes regularly on boil wash.
   This is because work clothes can also cause contamination.
6. Make use of phage rotation
   A phage is bacteria-specific. Rotating with different cultures, each containing different strains of bacteria, counteracts phage contamination. We call this phage rotation. These cultures give the same end product. Which frequency of phage rotation to use in this process is specific to each situation. A general guideline or advice here is:
   • Daily production up to several times a week: about once every four weeks.
   • Weekly production: about once every three months.

Ensuring continuous production of a high-quality end product

Phage contamination can cause a major problem for the production process, but fortunately there are measures to prevent contamination. Besides regular cleaning and disinfection of equipment and environment, phage rotation is a very effective way to reduce the risk of contamination. So that a high-quality, tasty and shelf-stable dairy product can be produced continuously.

Want to know more about the proper use of phage rotation with different cultures or advice on your cleaning process?

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