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The Detection of Formaldehyde in Milk by Means of the Methylene Blue Reduction Test¹

Kansas Agricultural Experiment Station, Manhattan, Kansas

ABSTRACT

It is possible to use the methylene blue reduction test as a basis for suspecting the presence of formaldehyde in milk. The addition of effective quantities of formaldehyde shortens the reduction time, especially if the methylene blue reduction test is run soon after the formaldehyde has been added. It is not intended, to imply that the methylene blue reduction test can be used as a specific test for the presence of formaldehyde, but that short reduction times may suggest the application of more exact qualitative tests for the presence of formaldehyde.

The range of dilutions of formaldehyde which effectively retarded bacterial growth, definitely delayed the coagulation time, and at the same time escaped detection by a majority of those who tasted the milk was between 1:15,000, and 1: 25,000. The addition of more than 1:15,000 formaldehyde is quite certain to be detected by the consumer, whereas less than 1: 25,000 fails to accomplish the purpose for which it is usually added. In other words, the dairyman must be able to adjust the final concentration within this rather narrow range. On a basis of the volume of commercial formalin the margin between "enough" and "too much" is only 0.25 cc. or about 5 drops per gallon. The chemical precision requisite for such careful adjustment is not usually to be expected outside of the laboratory. This suggests that the addition of formaldehyde to milk by the average dairyman is more likely to fail than it is to accomplish the intended result. The addition of too much is likely to be detected by the consumer or to arouse the suspicion of the milk plant operator by anomalous results of the methylene blue reduction test as outlined in this paper. Specifically, any sample of fresh milk which shows a reduction time of less than one hour may be suspected of containing formaldehyde, especially if the keeping quality or the bacterial counts are contraindicative.

¹ Contribution No. 160, Department of Bacteriology.