| In this project, the effect of freeze/thaw process on E. coli and spores of Bacillus megaterium survival was studied. The storage time, the concentration of salt and preserve temperature were the significant factors affecting E. coli's survival. The effect of freezing temperature on microorganism reduction is: -5°C > -35°C > -15°C. The cells at exponential growth phase were more sensitive to the freeze/thaw process than the stationary growth phase cells. In the spraying freezing test, samples collected two days after spraying, the number of E. coli surviving dropped dramatically. Bacillus megaterium spores reduction with freeze/thaw process showed stronger tailing phenomenon after UV exposure than without freezing. At low chlorine concentration (2.0 mg/L), this process made spores more resistant than at higher concentration (6.0 mg/L). It appeared that the freeze/thaw process caused damage to the cell structure, but also decreased the water activity and clumped the spores. In spraying freezing test, there was no significant effect on the survival of spores. |
