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Postharvest Decay Risk Associated with Hydrocooling Tomatoes

Tomatoes (breaker stage) hydrocooled with a cell suspension of Erwinia carotovora subsp. carotovora containing 50 to 200 mg of free chlorine per liter (ppm) (10°C, pH 7) remained decay free during a 10-day storage at 20°C. Sporadic disease appeared during storage of tomatoes similarly cooled with chlorinated water containing spores of Rhizopus stolonifer. In contrast, when chlorine was omitted from the pathogen suspensions, 50 to 100% of the fruit became diseased. A laboratory-scale shower hydrocooler reduced fruit temperatures from 35 to 15°C within 13.3 min, whereas a flume cooler produced the same temperature reduction in 10.5 min. In both systems, tomatoes increased in weight during cooling, evidence for water uptake. Larger weight increases occurred among tomatoes cooled in the shower than in the flume. An upward instead of downward orientation of stem scars under the shower streams led to significantly larger weight increases, presumably because pores in the stem scar were continuously flooded with water. Tomatoes intermittently submerged in cold water (10 2-min immersions followed by 30-s pauses) absorbed significantly less water than those continuously submerged for 20 min. Hydrocooling appears to be a viable method for rapid cooling of tomatoes. Technical refinements in the hydrocooling process that prevent continuous coverage of fruit surfaces by water should reduce water uptake and the associated risk of pathogen internalization. Maintenance of free chlorine at up to 200 ppm in the cooling water and prevention of direct water pressure on fruit should minimize decay risks. No evidence of phytotoxicity was observed among fruit infiltrated with 200 ppm of chlorine. These tomatoes ripened similarly to those that were not cooled or were cooled in tap water.