Delays to Blueberry Cooling and Effects on Storage Quality Under Commercial Conditions

Commercially grown blueberries are often harvested, partially cooled and held overnight for packing and final cooling the following day. However, consequences of this 24-hour delay on subsequent fruit quality have not been reported. Two tests were conducted in April and May 2015 on commercially harvested, southern highbush (Vaccinium corymbosum) blueberries (mixture of ‘Farthing’, ‘Sweetcrisp’, ‘Emerald’). Immediately after harvest six fruits were each fitted with a recording thermistor probe (2-mm diameter) and placed within the center of the fruit (+/- 3 kg) in each of six field lugs on the sixth layer from the base of a standard (100 cm X 120 cm) pallet. Probed fruit were positioned so as to measure pulp temperatures across the layer (air inlet, center, outlet) during partial forced-air (FA) cooling immediately after harvest. Half of these samples were packed into rigid, “clamshell” containers (312 g each; 8/carton), and FA cooled to final storage temperature. The other half were held overnight in the refrigerated packing area, and packed and FA cooled the following day. Following packing each probed fruit was repositioned in the center of a clamshell in the first three layers on the pallet to track pulp temperature during final forced-air cooling. Following final cooling, cartons were stored in the laboratory at 1°C/88% R.H. and analyzed over 21 d. Partial FA cooling lowered mean fruit temperature to 18^°C within 90 min of harvest; fruit held overnight cooled further to 10.6^°C prior to packing. Total time through final FA cooling was 6.3 hr (day of harvest) and 26.5 hr (following day). 7/8 Cooling was achieved during both cooling events. Storage time had a greater effect on blueberry quality than did the 24-hr delay to packing and cooling. Weight loss roughly doubled each 7 d to 1.83% after 21 d. Although fruit appearance was acceptable after 14 d, incidence of shriveling increased from 7.0% to 46% after 14 and 21 d of storage, respectively. Fruit remained firm throughout storage (1.67 N mm^-1); soluble solids content remained constant (10.2%), whereas total titratable acidity decreased by approximately 20% to 0.44% (citric acid basis). Decay was minimal after 21 days (4%). Based on these results, rapid cooling to 18^°C within 90 min of harvest permitted blueberries to be held overnight and packed the following day with minimal negative effects on quality during subsequent storage. Delays from harvest to initial cooling, though not tested here, may negatively affect quality during shipping.