An Assessment of the Decay Hazard Associated with Hydrocooling Strawberries

Abstract

The decay hazard associated with hydrocooling strawberries was related to whether they became inoculated with postharvest pathogens during the procedure. Storage of hydrocooled berries at warmer temperatures or for longer periods than recommended allowed inoculation to be expressed into disease. Cooling strawberries by immersion hydrocooling did not consistently lead to increased postharvest decays when compared with conventional forced-air cooling in two separate trials. No differences in decay incidence were found in berries that were hydrocooled versus forced-air cooled and then stored 7 days at 1°C plus 1 day at 20°C. With a 15-day storage regime (14 days at ≤7°C plus 1 day at 20°C), hydrocooled fruit developed less decay than forced-air-cooled fruit in one trial but more decay in a second. Wrapping baskets of cooled berries with plastic film promoted disease development and slowed the moisture loss from both hydrocooled and forced-air-cooled berries. The wrap did not promote disease more when applied to wet, hydrocooled berries as compared with dry, forced-air-cooled berries. Residual moisture left on the berries by the hydrocool treatment did not predispose the fruit to postharvest decays. In contrast, wounds and abrasions on hydrocooled fruit were temporarily water soaked and berries typically increased in weight as they were hydrocooled. Berries cooled in water containing spores of Botrytis cinerea or Rhizopus stolonifer developed nearly 100% decay incidence during a storage regime that favored specific development of gray mold (11 days at 7°C) or Rhizopus rot (2 days at 24°C). Chlorinating the hydrocooler water (120 mg of free chlorine per liter at pH 6.5) before adding the berries and spores reduced the incidence of gray mold to 43%; in contrast, berries hydrocooled in clean water developed 61% gray mold. Chlorination of the clean water led to significant reductions in the incidence of gray mold (44%) but did not affect the incidence of Rhizopus rot. The hydrocool method for cooling strawberries with the addition of proper chlorination has promise as a rapid method for cooling and cleaning berries and reducing gray mold inoculum on berry surfaces.