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Research offers improvements for commercial strawberry handling

Strawberries are very fragile and highly susceptible to mechanical injury during commercial production.

Strawberries are very fragile and highly susceptible to mechanical injury during commercial production.

Growers interested in ways to increase profits and reduce product loss are seeking improved handling and temperature management techniques. Collaborative research from scientists from the Brazilian Agricultural Research Corporation—Embrapa and the University of Florida contains several findings that show promise to significantly improve commercial strawberry handling.

Because of their fragile nature, strawberries must be harvested when they are ripe to minimize bruising, a critical concern leading to product and revenue losses for growers. Bruising is caused by impact, compression, and vibration forces. Impact bruising results from a sudden sharp force – for example, when a fruit falls onto another fruit or onto a hard surface, or when an object strikes the fruit. Compression bruising occurs when tissue is subjected to a constant force such as that undergone during hand-harvest (finger pressure), or when the fruit is on the bottom layer of a container.

To replicate commercial handling conditions, the research team used forced-air or hydrocooling with three strawberry cultivars (Chandler, Oso Grande, and Sweet Charlie) to help them reach pulp temperatures of 1 or 30 Celsius. The fruit was then subjected to compression and impact forces and subsequently evaluated for bruising; each berry was sliced through the centre of the impact area. It was considered bruised if damaged tissue was visible below the impact area.

According to the study results, strawberries with a pulp temperature of 24 Celsius exhibited sensitivity to compression but greater resistance to impacts. As pulp temperature decreased, fruit were less susceptible to compression, as shown by up to 60 per cent reduction in bruise volume. In contrast, strawberries at 1 Celsius pulp temperature had more severe impact bruising, with up to 93 per cent larger bruise volume than at 24 Celsius, depending on the cultivar.

The strawberries also showed different susceptibility to impact bruises, depending on the cooling method. Impacted fruit that were forced-air cooled had larger bruise volumes than those that were hydrocooled. The impact bruise volume for strawberries forced-air cooled to 1 Celsius was 29 per cent higher than for fruit hydrocooled to 20 Celsius, 84 per cent higher than for those forced-air cooled to 20 Celsius, and 164 per cent higher than for those hydrocooled to 1 Celsius.

The results proved that strawberries had different responses to compression and impact forces based on pulp temperature. Fruit at low temperature were more resistant to compression, while fruit at higher temperatures were more resistant to impact. This finding translates to practical recommendations for commercial strawberry growers, suggesting that fruit bruising caused by compression may be minimized by harvesting and transporting early in the day when pulp temperatures are lowest.

“There is potential for strawberries to be graded and packed on a packing line,” states the report. “However, impact bruising at transfer points must be minimized. In this scenario, the strawberries could be harvested into field lugs (two or three layers deep of fruit) and transported to the packinghouse. It would be more advantageous to use hydrocooling than forced-air cooling because hydrocooling cools fruit at a much faster rate.”

The authors added that because incidence and severity of impact and compression bruises are temperature-dependent, strawberry growers should consider pulp temperature for harvest scheduling and for potential grading on a packing line.

“Hydrocooling shows to rapidly cool strawberry fruit while reducing weight loss and bruising sensitivity,” the researchers concluded.

The complete study and abstract are available on the ASHS HortScience electronic journal website: http://hortsci.ashspublications.org/cgi/content/abstract/44/7/1953