Purpose: Evaluation of forced-air cooling (FAC), and hydrocooling with (HCS) or without sanitizers (HC) for microbial quality control of blueberries.
Methods: A cocktail of five rifampicin-resistant Salmonella enterica strains (Newport, Javiana, Enteritidis, Typhimurium and Braenderup) was utilized. Freshly harvested blueberries (170 g in 6-oz clamshell per replicate) were spot-inoculated with 10 µl inoculum, resulting in seven log CFU/blueberry, and were left to dry for one hour. Four sets, each consisting of three clamshells, were used in the experiments. One set was placed under a modified forced-air cooling unit for 60 to 90 minutes. One set each was hydrocooled for six minutes (with agitation) by complete immersion in water i) containing 150 ppm HOCl sanitizer solution and ii) without sanitizer. After hydrocooling, drained clamshells were placed on paper towels and weighed. All sets, including a control set (inoculated but not treated) were stored at 2°C and Salmonella was enumerated on days 0, 1, 3, 5, 7, 14, and 21 after inoculation.
Results: The FAC showed no significant effect (P>0.05) on the microbial quality of blueberries. The HC alone reduced the initial number (5.7 log CFU/g blueberries) of Salmonella significantly (P<0.01) on day 0. This decrease was most probably due to the mechanical action of the hydrocooling water washing the inoculum off the surface of the blueberries. Hydrocooling with sanitizer highly significantly (P<0.0001) decreased the number of inoculated Salmonella by >4 log CFU/g blueberries over 21-days incubation.
Significance: Hydrocooling, with or without sanitizer, of blueberries shows promising result in postharvest microbial quality control and storage of the fruits. Information obtained will be used for recommending the best temperature management to maintain postharvest quality of blueberries.