The Microbicidal Activity of Gaseous Propylene Oxide and Its Application to Powdered or Flaked Foods

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Abstract
SUMMARY: The sporicidal activity of gaseous propylene oxide was determined at several concentrations and at low and high relative humidity (RH). At 37°C, 85% RH, and a concentration of 1250 mg/L, propylene oxide will kill 90% of a population of dry spores of B. subtilis var. niger in one hour. If RH is lowered to 25% under the same conditions, 90% of the spores are killed in 40 minutes. Microbial decontamination of several flaked or powdered foods with propylene oxide was determined in 4‐L rolling jars or in a 4‐cu‐ft revolving blender. The bacterial count of cereal flakes inoculated with dry spores of B. subtilis var. niger was reduced 95% in 4 hours at 37 and 55°C, hut further reduction in count was achieved only after prolonged holding times. Studies with cocoa powder showed that exposure to a propylene oxide concentration of l‐2% by weight of cocoa (or 1000‐2000 mg/L of space) at 37°C for 2‐3 hours reduced bacterial count by 50‐70% and thermophilic count by 50‐90%. Destruction of molds and vegetative bacteria in cocoa or other foods was 90‐99.9% under these conditions. Destruction of the microbial flora of cocoa was greater when the treated Cocoa was stored with some residual propylene oxide in bottles or plastic bags. Addition of liquid propylene oxide directly to small samples of cocoa gave good reduction of the microbial flora, but also some physical destruction of the contents.

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