MICROBIOLOGICAL CONTROL OF CUCUMBER HYDROCOOLING WATER WITH CHLORINE DIOXIDE

The time required to cool size 2B (3.43 to 3.75-cm-diameter) pickling cucumbers by a commercial spray-type hydrocooler to less than 9 degree s C was about Is min at typical initial fruit temperatures of 25 to 29 degrees C. During this period, the fruit was exposed to the recycled water, which reached relatively high populations of bacteria (10(6) to 10(7) colony forming unites [CFU]/g total aerobes and 10(5) to 10(6) CFU/g total Enterobacteriaceae) during a typical day's operation. Thes e numbers exceeded those present on the unwashed fruit, depending upon the volume of fruit previously cooled. Residual chlorine dioxide at 1 .3 ppm was found to optimally control (2 to 6 log-cycles reduction) th e numbers of bacteria. At 0.95 ppm chlorine dioxide, the numbers of ba cteria in the water were relatively static, while at 2.8 and 5.1 ppm t he odor of chlorine dioxide became excessive. The bacterial population s in/on the cucumbers were not greatly influenced by chlorine dioxide, even at 5.1 ppm. Apparently, microorganisms on or in the fruit were p rotected from the chlorine dioxide. Thus, the use of chlorine dioxide in hydrocooling water of cucumbers seems to be an effective means of c ontrolling microbial build-up in the water, but has little effect upon microorganisms on or in the fruit.