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Listen to this siteMonday 18 November 2002
This research project aims to consider the feasibility of identifying unpasteurised milk in species other than cows.
Study Duration : April 2001 to June 2002
Contractor : Hannah Research Institute
The Food Standards Agency Scotland has undertaken a project to consider the feasibility of identifying unpasteurised milk in species other than cows: "Variabilty of alkaline phosphatase in goat and sheep milk in relation to its use as an effective index of pasteurisation". This work is targeted at reducing the potential threat to public safety associated with drinking inadequately processed goat and sheep milk.
The microbiological safety of milk depends on efficient pasteurisation and prevention of recontamination of the finished product with bacteria. Pasteurisation is a heat treatment equivalent to a minimum holding of milk at no less than 71.8°C for 15 seconds which inactivates potentially harmful bacteria found in raw milk. The test to determine the effectiveness of pasteurisation in pasteurised milk is called the alkaline phosphatase test. The test was developed in the 1930s when scientists found the enzyme alkaline phosphatase (ALP), which is present in milk from all species, was inactivated at slightly higher temperature conditions than those required to kill Mycobacterium tuberculosis , the organism responsible for tuberculosis. This heat treatment was also shown to effectively destroy other milkborne bacteria that may cause human disease.
Validation of the effectiveness of the pasteurisation process is based on the destruction of a natural milk enzyme, ALP. The effectiveness of this test hinges on the initial concentration of ALP in raw milk, determining the amount of ALP remaining active after pasteurisation. The detection limit for the reference test for ALP is equivalent to the contamination of properly pasteurised cows' milk by 0.1% raw milk. However, the amount of ALP in milk varies between species and within individual animals within a species.
In this study, the implications of applying the test to pasteurised goats' milk were explored as goats' milk is reported to have natural levels of ALP around 10% of that found in cows' milk. Therefore, in such circumstances, the sensitivity of the test for ALP is reduced tenfold, i.e. contamination by raw milk could reach a level of 1% before a pasteurised milk would fail the current statutory ALP test.
Before this study, detailed information regarding the ALP levels in goats' milk was not available. Consequently an investigation was undertaken to explore factors influencing changes in ALP levels in 12 British Saanen goats throughout a full lactation.
ALP levels in goats' milk were shown to be extremely variable in individual animals within a herd. More importantly, levels of ALP in goat milk were consistently at least tenfold lower than those found in cows' milk. Herd goat milk in early lactation contained the lowest levels of ALP and a 1% contamination of pasteurised milk with raw milk did not produce a fail in the current statutory colorimetric ALP test.
It was shown, however, that the more sensitive tests of bioluminescence and fluorescence could be used to detect a 0.2% contamination of pasteurised goats' milk with raw milk in early lactation but to use these tests effectively, the current legislative limit for ALP in pasteurised goats' milk would have to be reassessed and reduced considerably. Ideally, new test methods are required to assess the effectiveness of pasteurisation of goats' milk.
The final report is available from the FSA Library and Information centre. To obtain a copy, please contact the Enquiry Desk, Dr Elsie Widdowson Library and Information Services, Food Standards Agency ( tel: 020 7276 8181/8182 or email: library&info@foodstandards.gsi.gov.uk )
Contact
: For any enquiries concerning this research project, please contact the relevant programme contact or email:
science@foodstandards.gsi.gov.uk
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