Commercial Scale Hydrocooling of Fresh Market Strawberry

Strawberry flavor and appearance is best for fruit picked full-ripe. However, ripe strawberries soften faster and are more susceptible to bruising, decay, moisture loss, and shriveling. Therefore, commercial operations typically pick fruit ¾-ripe, field-pack into rigid clamshell containers, place in corrugated cartons, palletize, and forced-air cool (FAC). However, achieving 7/8 cooling time for FAC can vary from 60-120 min and final pulp temperature can vary within the pallet. A 6-h delay to FAC can reduce strawberry quality after 7 d storage; such fruit are softer, lose more weight, and have lower total sugars and ascorbic acid content than fruit cooled shortly after harvest. Previous tests using immersion hydrocooling (HC) with sanitized water showed promise for strawberry shippers, in that fruit were uniformly cooled in approximately 13 min, potentially increasing throughput by 4- to 8-fold. HC strawberries in clamshells cooled at the same rate as those in bulk; after 14 d at 2 ^oC, quality of HC fruit was equal to or better than FAC fruit. In Spring 2014, strawberries (‘Red Merlin’, ‘Florida Strawberry Festival’, ‘Radiance’) were field-packed into 1-lb clamshells and placed in either corrugated cartons (FAC; eight clamshells/carton) or returnable plastic containers (RPC) (HC; nine clamshells/RPC). Twenty-eight RPCs (stacked two high) were sequentially immersed in a semi-commercial flume HC system installed at the cooling facility. Water (1.2 ^oC, 180 ppm free chlorine) was concurrently circulated (2,800 L/min) with the RPCs, achieving 7/8 cooling in approximately 15 min; RPCs were then drained (15 s), palletized (five/layer) and stored in the cold room (1.2 ^oC) for 15 d. Pulp temperatures were monitored in top (one probe) and bottom (two probes) layers during HC. For FAC, palletized cartons (six/layer) were arranged in tunnels (four pallets/side); pulp temperatures were monitored on the air inlet and outlet sides (three fruit/side). After 75 min fruit were moved to the cold room.  Following cooling FAC pulp temperatures ranged from 3^o to 8 ^oC, whereas HC fruit ranged from 2^o to 3 ^oC. However, fruit quality from both cooling treatments was similar during storage. Strawberry appearance decreased from 9.0 (Day 1) to 6.4 (Day 8) (appearance ratings: 9=excellent; 5=limit of marketability; 1=extremely poor), but was unmarketable by Day 15. Soluble solids content, total titratable acidity and anthocyanin content were 6.79%, 1.48% and 19.7 mg/100 g, respectively. Although HC fruit retained free moisture during storage, decay was low (<2%) for both treatments by Day 15.