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Appl Environ Microbiol. 1962 September; 10(5): 431-435

Eflect of Relative Humidity on the Bactericidal Activity of Propylene Oxide Vapor¹

Institute of Agricultural and Industrial Microbiology, University of Massachusetts, Amherst, Massachusetts

ABSTRACT

Because of the low toxicity of its breakdown product, propylene oxide (PO) vapor will play an increasingly important role in the preservation of foods. It is therefore necessary that the diversified variables which influence effectiveness of PO treatment be thoroughly investigated and understood prior to advocating its general use in industry. Accordingly, the present study was undertaken to determine the effect of relative humidity (RH) upon the bactericidal activity of PO sterilant atmospheres. Death rates were established at increasing RH values of < 1, 52, 65, 80, and 98% and under constant conditions of concentration, pressure, and temperature. Test bacterial populations were preconditioned to corresponding moisture levels. Results indicate that gram-positive cocci were relatively insensitive to PO vapor at dry conditions but became progressively less resistant with the increase in RH up to a maximum of 65 to 70%. Lactic acid bacteria and gram-negative rods were much more sensitive at dry conditions, showing much less dependency upon water vapor. Bacillus subtilis spores elicited the highest degree of resistance but the death rate substantially increased with the increase in RH.

² Present address: Robert A. Taft Sanitary Engineering Center, Cincinnati, Ohio.

¹ Contribution No. 12 of the University of Massachusetts, College of Agriculture Experiment Station, Amherst.