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pp.250-256
To verify the multiplication of microorganisms on the surface of strawberries, the fate of E. coli DH5α::gfp at different temperatures, times and strawberry extract concentrations were measured. The population of E. coli DH5 α::gfp rapidly increased by 7.36~7.78 log CFU/g at 25~30℃ for 24 hr and slowly increased by 6.49~8.49 log CFU/g at 10~20℃ for 48 hr. However, E. coli DH5α::gfp did not grow at 10~15℃ on the surface of the strawberries, regardless of the contact times with the bacterial suspension. E. coli DH5α::gfp reached 1.52~3.26 log CFU/g at 20℃ as the contact frequency increased from two to six times. The contact frequencies did not significantly differ. In the case of the six-time contact on the surface of the strawberry at 25 and 30℃, the E. coli DH5α::gfp increased by 5.17 and 5.01 log CFU/g. The effects of the strawberry extracts on the growth of E. coli DH5α::gfp showed that sterilization and non-sterilization do not affect the growth of microorganisms for 96 hr. In the minimal broth, the growth of E. coli DH5α::gfp increased by 1 log CFU/g for 96 hr. In less than 50 percent of the strawberry extracts, the growth rate of E. coli DH5α::gfp was higher than in the control and increased by 4 and 5 log CFU/g at 50 and 25 percent of strawberry extracts, respectively. Therefore, E. coli DH5α::gfp can multiply and survive on the surface of strawberries when it comes into contact with the fruit extract.
