Hydrocooling, Forced-air Cooling and Hydrocooling Plus Forced-air Cooling of Two Southern Highbush Blueberry Cultivars and Effects on Fruit Quality

Blueberry is widely produced in the USA and around the world. Fruits are harvested fully ripe and, as such, are highly perishable. One strategy to maintain fruit quality during commercial handling is rapid cooling. Currently blueberries are forced-air cooled for 60 to 90 min to 2 to 3 ^oC pulp temperature. Hydrocooling is an effective cooling method widely used for many crops such as peach, cherry, avocado, mango, sweetcorn, and carrot. Hydrocooling is also a potential cooling method for blueberry. The objective of this work was to compare the cooling efficiency of forced-air cooling (FA) with hydrocooling (HY) and with hydrocooling plus forced-air cooling (HY+FA) and the effects on blueberry fruit quality. ‘Emerald’ and ‘Farthing’ (Vaccinium corubosum) are widely grown southern highbush cultivars released from the University of Florida breeding program. ‘Emerald’ is a vigorous, high-yielding cultivar with large fruit and good shipping quality. ‘Farthing’ has high quality, with dark peel color and exceptionally firm texture. ‘Emerald’ and ‘Farthing’ blueberries were commercially harvested and cooled using the three methods. FA was accomplished in a small-scale unit within a cold room with air maintained at 1 ^oC; there was 15.2 mm pressure drop across the plenum during a 27-min treatment period. For HY, fruits in clamshells (125 g) were immersed in chlorinated ice-water (200 ppm free Cl^-1) for 3 min. For HY+FA, following HY the clamshells were transferred to FA for 30 min. After cooling treatments, the clamshells were stored at 1 ^oC for 21 d and the fruit quality, weight gain/loss, appearance, freshness, firmness, bloom, anthocyanin content, soluble solids content, pH, titratable acidity, decay and bruising were determined weekly. ‘Emerald’ was more sensitive to HY than ‘Farthing’, where several fruit from the former showed skin breaks. The initial firmness for ‘Farthing was 3.5 N for all treatments and decreased to 2.9 N after 21 d while for ‘Emerald’ the initial firmness was 2,7 N and decreased to 2,4N during storage. The anthocyanin content for ‘Emerald’ decreased by 33% during 21d of storage when treated with HY+FA cooling, whereas for ‘Farthing’ the average of the anthocyanin content remained at 8.3 mg PGN g^-1 for all treatments during storage. ‘Emerald’ was less acidic with 0.3 % citric acid and sweeter (10.2 % soluble solids content) than ‘Farthing’ with 0.6% citric acid and 9.4 % soluble solids content for all treatments. Both cultivars had no decay during storage.