Sunday 26 October 2014

The heat-resisting bacteria

John Donworth

Published 27/05/2008 | 00:00

Teat skin is a favourite environment for Thermoduric bacteria

Dairy farmers are very familiar with TBC and SCC levels in their milk supply. They know that if they go under a certain standard they will be penalised. All milk processors in Ireland penalise or reward farmers for their TBC and SCC levels. It is an accepted fact that elevated levels of both causes difficulty in the manufacture of product.

In recent years, another group of bacteria has come under the radar screen and some milk processors will now penalise elevated levels of this bacteria. These bacteria are called thermoduric bacteria.

Why are thermoduric bacteria a problem? Thermoduric bacteria have developed mechanisms to resist heat. They have an ability to create a protective spore. These spores end up in finished products. They can begin growing, and as a consequence damage product.

Pasteurisation of raw milk kills the vast majority of bacteria that are likely to cause potential damage. However, some survive this process and those that do are the so-called thermoduric bacteria.

Thermoduric bacteria are organisms that exist in the environment. They exist in the soil, on silage, faeces, bedding, teat skin and water. They also exist in deposits on the internal surfaces of milking machines and bulk tanks.

Good hygiene

So, how can the dairy farmer minimise thermoduric levels? Good hygiene is the key. Not alone does this apply to the cow, but it also applies to her environment. For instance, approach roads to the parlour, collecting yards, cubicle beds and passageways. How clean are they?

The cow herself, for instance, has her tail been clipped? And lastly, if you are washing cows' teats they should be dried with paper towels, where necessary. This last one will obviously slow down cow flow through the parlour.

Milk residues provide an ideal breeding ground for thermoduric bacteria. Dull areas on stainless steel will indicate a build up of residues. You will find milk residues in the bulk tank, in the milk filter, in the clawpiece, in the milk pump diaphragm, in the plate cooler, in the milk line and in the receiver jar.

I know if you are having TBC problems with the machine, all the above areas will get a thorough checking out. But one area, not mentioned above, can be a major source of thermoduric bacteria.

This area is the rubberware on the plant. As rubberware get older, it starts to crack. This allows bacteria to live in the rubberware. Here, they remain protected from hot water and chemicals. Exposure of rubberware to chlorine for long periods, will cause rubber to deteriorate more quickly.

Hence, it is vitally important that cleaning products are used in the correct way.

Cooling milk correctly

All bacteria, including thermoduric bacteria, increase rapidly in numbers if milk is cooled slowly or inadequately. Milk should be cooled within 30 minutes of milking, down to four degrees C, or below. Issues such as blend temperatures and collection days are also important.

So, it appears that the secret to low thermoduric levels is good hygiene. Is good hygiene becoming more difficult to achieve as parlour size increases and dairy farmers are asked to handle more units and more cows?

A Moorepark on-farm study in 2007, covering over 400 farms, found that 16pc of dairy farmers don't use a detergent after their afternoon milking; 14pc use a hot wash once a year, or never; 19pc do not use any milk filters; 45pc do not use any teat preparation; 64pc change liners once a year, or less; 39pc clip cow tails once a year, or less; and only 17pc clean collecting yards after each milking session.

The test that determines the number of thermoduric bacteria in milk is the Laboratory Pasteurisation Count (LPC). This test is used as an indicator of the effectiveness of farm sanitation and hygiene procedures. This test mimics pasteurisation, in that a sample of milk (5ml) is heated to 145°F (62.8°C), held for 30 minutes at that temperature, and then cooled. The number of bacteria that survive the test are counted.

Dairy farmers are penalised when the LPC figure goes above 1,000/ml. Counts greater than 300/ml are generally considered indicative of some source of contamination.

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