Microbiological Control of Cucumber Hydrocooling Water with Chlorine Dioxide ^†

Area of Science:

• Food Science
• Microbiology
• Agricultural Engineering

Background:

• Hydrocooling is a common method for cooling pickling cucumbers.
• Recycled hydrocooling water can accumulate high levels of bacteria, potentially exceeding those on unwashed fruit.
• Controlling microbial growth in hydrocooling systems is crucial for food safety.

Purpose of the Study:

• To evaluate the effectiveness of chlorine dioxide in controlling bacterial populations in hydrocooling water for pickling cucumbers.
• To determine the optimal concentration of chlorine dioxide for microbial control without causing excessive odor.
• To assess the impact of chlorine dioxide on microorganisms present on or within the cucumbers.

Main Methods:

• Pickling cucumbers (size 2B) were cooled in a spray-type hydrocooler.
• Bacterial populations in the hydrocooling water and on the fruit were quantified.
• Chlorine dioxide was added to the recycled water at various concentrations (0.95, 1.3, 2.8, and 5.1 ppm).
• Microbial reduction was measured using colony forming units (CFU) per gram.

Main Results:

• Hydrocooling to below 9°C took approximately 18 minutes for cucumbers initially at 25-29°C.
• Recycled water reached high bacterial counts (10^6-10^7 CFU/g total aerobes).
• Chlorine dioxide at 1.3 ppm optimally reduced bacteria in water (2-6 log-cycle reduction).
• Higher chlorine dioxide concentrations (2.8, 5.1 ppm) resulted in excessive odor.
• Bacterial populations on or in cucumbers were minimally affected by chlorine dioxide.

Conclusions:

• Chlorine dioxide is effective in managing microbial proliferation within hydrocooling water for cucumbers.
• Optimal chlorine dioxide concentration for water microbial control is around 1.3 ppm.
• Chlorine dioxide has limited efficacy in reducing microorganisms on or within the cucumber fruit, likely due to protection from the fruit surface or internal tissues.