Hostname: page-component-77c89778f8-rkxrd Total loading time: 0 Render date: 2024-07-18T23:44:45.026Z Has data issue: false hasContentIssue false
  • English
  • Français

The water agar test: a new test to measure the bacteriological quality of cream

Published online by Cambridge University Press:  15 May 2009

Margaret M. Taylor
Margaret M. Taylor
Affiliation:
The Hannah Research Institute, Ayr KA 6 5HL
Rights & Permissions [Opens in a new window]

Summary

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

A new test, the water agar test, is described that gives a qualitative index of the presence of bacteria that indicate contamination of the cream, poor storage conditions or both of these factors. The method is simple and requires little equipment. The bacteria grow in a film of diluted cream adsorbed on the surface of a non-nutrient base. After incubation at 30 ± 0.5° C. for 18–20 hr., a proteolytic and mucoid colony count is obtained which has the same percentage coefficient of variance as a standard plate count.

An examination of the effect of storage at different temperatures on the types of bacteria present in cream showed that of all the tests done initially, only the water agar test could predict subsequent bacterial growth with any consistency. The multiplication of presumptive coliform organisms occurred even at 3.5° C. Irrespective of the colony count, the methylene blue reduction time was not shorter than 7½ hr. unless the bacteria were in the logarithmic phase of growth when sampled.

A survey was made of the bacterial flora of 188 retail samples of double cream of 15 different brands. The age of the samples varied from freshly separated cream to cream that had been kept in the shop for a day longer than that recommended for sale. The water agar test was compared with the colony count, the presumptive coliform test, a confirmatory coliform count in violet red-bile agar, a lipolytic colony count, a staphylococcal count and the methylene blue reduction test.

Type
Research Article
Information
Journal of Hygiene , Volume 74 , Issue 3 , June 1975 , pp. 345 - 357
Copyright
Copyright © Cambridge University Press 1975

References

REFERENCES

Ayres, S. H. & Mudge, C. S. (1920). Milk-powder agar for the determination of bacteria in milk. Journal of Bacteriology 5, 565.CrossRefGoogle Scholar
British Standards Institution. Methods of microbiological examination for dairy purposes. British Standard 4285: 1968.Google Scholar
British Standards Institution (1970). Methods of microbiological examination of milk products. Supplement no. 1 (1970) to British Standard 4285: 1968.Google Scholar
Cheeseman, G. C. (1963). Action of rennet and other proteolytic enzymes on casein in caseinagar gels. Journal of Dairy Research 30, 17.CrossRefGoogle Scholar
Chilson, W. H. & Collins, M. A. (1940). Application of the resazurin test in determining the quality of pasteurized cream. Journal of Milk Technology 3, 334.CrossRefGoogle Scholar
Department of Health for Scotland Memorandum. No. 9/46 (Revised 1955). Scottish Milk Testing Scheme.Google Scholar
Higginbottom, C. (1941). The examination of raw milk by the methylene blue and resazurin tests and by the plate count. Proceedings of the Society of Agricultural Bacteriologists 4, 32.CrossRefGoogle Scholar
Hobbs, B. C. (1939). The part played by bacteria in the reduction of methylene blue. Journal of Dairy Research 10, 35.CrossRefGoogle Scholar
Jezeski, J. J. & Macy, H. (1946). Cryophilic organisms in water and butter. Journal of Dairy Science 29, 439.CrossRefGoogle Scholar
La Grange, W. S. & Nelson, F. E. (1965). Evaluation of dye reduction tests for manufacturing-grade bulk-tank milk. Journal of Dairy Science 48, 1129.CrossRefGoogle ScholarPubMed
Morris, C. S. (1941). Cryophilic bacteria as a cause of milk samples failing the methylene blue test. Proceedings of the Society of Agricultural Bacteriologists 4, 33.CrossRefGoogle Scholar
Milk (Special Designations) Order (1936). Statutory Rules and Orders, 1936, No. 356.Google Scholar
Milk (Special Designation) Regulations (1963). Statutory Instruments, No. 1571: 1963.Google Scholar
Mossel, D. A. A. (1974). Bacteriological safety of foods. Lancet i, 173.CrossRefGoogle Scholar
Report (1939). The bacteriological examination of water supplies. Reports on Public Health and Medical Subjects, Ministry of Health, London, no. 71.Google Scholar
Report (1958). The bacteriological examination and grading of fresh cream. Report of a working party of the Public Health Laboratory Service. Monthly Bulletin of the Ministry of Health and the Public Health Laboratory Service 17, 77.Google Scholar
Report (1971). The hygiene and marketing of fresh cream as assessed by the methylene blue test. Report of a working party of the Public Health Laboratory Service. Journal of Hygiene 69, 155.CrossRefGoogle Scholar
Taylor, M. M. (1967). A hygiene test for milk. Dairy Industries 32, 278.Google Scholar
Taylor, M. M. (1971). The water agar test for rapid estimation of psychrotrophs. Dairy Industries 36, 400.Google Scholar
Thomas, S. B., Druce, R. G., Davies, A. & Bear, J. S. (1966). Bacteriological aspects of bulk milk collection. Journal of the Society of Dairy Technology 19, 161.CrossRefGoogle Scholar
Zoller, H. F. (1923). The value of milk powder agar in the bacteriological laboratory. American Journal of Public Health 13, 384.CrossRefGoogle ScholarPubMed