Report of the National Study on the Microbiological Quality and Heat Processing of Cows' Milk

Friday 21 March 2003

The national study on the microbiological quality and heat processing of cows' milk took place over a period of 18 months, between March 1999 and August 2000. Results from the study were presented to the Advisory Committee on the Microbiological Safety of Food at meetings in September 2000 and December 2000.

The papers and the advisory committee's comments were subsequently published on the Agency's website. This report draws the results together and provides further information on processing conditions and staff training.

All the dairies that volunteered to take part in the survey were included and this comprised a sample of 34% of approved dairy establishments throughout the UK which heat treat milk. The main objectives of the study were to obtain data on the microbiological quality of cows’ milk in the UK before and after heat processing and to analyse details of the production process by which the milk was heat-treated.

At the time the survey was being planned concerns were developing over the possible presence of Mycobacterium avium subspecies paratuberculosis (MAP) in pasteurised milk. The suggestion that it may be linked with the development of Crohn’s disease, coupled with experimental work which pointed towards the bacteria being able to survive pasteurisation, led to the Advisory Committee on the Microbiological Safety of Food (ACMSF) advising that MAP be included amongst the organisms to be sampled in the survey.

A total of 2036 samples were examined in this survey: 610 raw, 1413 pasteurised and 13 ultra heat-treated (UHT). A range of microbiological examinations were carried out on milk samples including total viable count (TVC), coliforms, coagulase positive staphylococcus, E. coli, E. coli O157, Listeria spp., L. monocytogenes, Salmonella spp., Campylobacter spp., Mycobacterium avium subsp. paratuberculosis (MAP) and M. bovis. Processing, staff and training details were also collected.

Although the majority of samples of pasteurised milk were of satisfactory microbiological quality, a number were found to contain coliforms and E. coli. This suggests possible post pasteurisation contamination, and therefore that, in some cases, improvements could be made by the industry.

Viable MAP was found to be present in a small percentage of pasteurised milk samples, some of which had been heated for 25 seconds. This appears to confirm laboratory studies demonstrating the relative heat resistance of this organism and suggesting that MAP will survive HTST (high temperature short time) pasteurisation.

The survey provides a baseline for any subsequent assessment of the levels of MAP and faecal contamination in raw and pasteurised milk. The intention is to evaluate the effectiveness of the MAP strategy by repeating the survey at a future date.