Mechanical Harvest of Southern Highbush Blueberries: Influence of Harvest Interval, Delay to Impact, and Pulp Temperature at Impact on Postharvest Quality

Fresh market blueberry (Vaccinium spp.) fruits are fragile and experience numerous impacts during harvest, packing, and shipping. Mechanical harvest of southern highbush blueberries (SHB) is being increasingly implemented due to rising costs and limited availability of labor. As new commercial cultivars become available, questions arise among growers as to their suitability for mechanical harvest. Early spring harvests in growing areas in the southeastern U.S. routinely occur when ambient temperatures exceed 30 °C. A series of experiments was conducted over a decade to determine the effects of mechanical impacts on fruit quality. These experiments employed a 60 cm drop height to induce bruising under three scenarios encountered during commercial harvest and handling. (1) Harvest interval: Nonimpacted ‘Star’ and ‘Sweetcrisp’ fruits had higher soluble solids content to titratable acidity ratios (SSC:TA) after a 7-day interval (Harvest 2) as compared with those from the initial Harvest 1. Impacted ‘Star’ blueberries from Harvest 2 were 70–100% softer during 14-d storage at 1 °C/85% relative humidity than those from Harvest 1, whereas ‘Sweetcrisp’ fruits were less affected by the harvest delay (30–40% increase in soft fruit). (2) Pulp temperature at impact: There were no differences in bruise severity for ‘Meadowlark’, ‘Colossus’, or ‘Sentinel’ due to pulp temperature at impact. Overall, impacted fruits consistently exhibited greater weight loss (3% to 9%), were softer, and had more severe bruising compared with nonimpacted controls. (3) Delays between harvest and impact: Delay-to-impact (5 or 24 h) did not affect weight loss for ‘Meadowlark’ (0.57% to 0.62%) during 4 d of storage at 5 °C. ‘Colossus’ and ‘Sentinel’, held overnight at 22 °C, lost approximately 35% to 45% more fresh weight after the 24 h delay to impact compared with those fruits with the 5 h delay to impact. Impacted blueberries exhibited significantly more severe bruising (38.5% to 84.4%) than control fruits (1.0% to 8.3%). ‘Sentinel’ was softer at harvest than the other cultivars and had the highest amount of severe bruising (82.7%), followed by ‘Meadowlark’ (52.67%) and ‘Colossus’ (42.57%). Flavor profiles varied by cultivar, with SSC:TA ratios ranging from 18 (‘Colossus’) to 21 (‘Meadowlark’) to 44 (‘Sentinel’). Immediately after impact at 15 °C, 20 °C, or 30 °C, the respiration rate (RR) for ‘Meadowlark’ increased as compared with the control fruit. RR for fruits at 5 °C or 10 °C remained fairly constant during the 8 h measurement period. These findings highlight the interactions of harvest interval, pulp temperature, and delay to impact on the postharvest quality of several commercially grown, SHB cultivars over this extended period of time. These three factors must be considered in order to develop effective strategies for mechanical harvest under the warm spring conditions encountered in the subtropical growing conditions in the southeastern U.S.A.