Reprinted from Northeast Sustainable Agriculture Research & Education 2020 Annual Report.
The Northeast strawberry season is the epitome of the phrase, “short and sweet.” On average, the average harvest lasts only three to four weeks, but consumer demand is strong (strawberries are the most consumed berry in the U.S.) and increasing, especially for local berries. In an effort to extend the local strawberry season, Thomas Gianfagna of Rutgers University studied advanced packaging technologies through a project funded by a Northeast SARE Research for Novel Approaches Grant.
Gianfagna examined the use of modified atmospheric packaging and essential oils to prolong fruit freshness and storage life as compared to conventional storage strategies.
Modified atmospheric packaging (MAP) is widely used in today’s food packaging; typically, levels of oxygen inside food containers are lowered to reduce oxidation, or carbon dioxide levels are increased to inhibit ripening. In this project, Gianfagna experimented with MAP bags outfitted with carbon dioxide emitters to reduce water loss in the berries. Fruit were evaluated in bags used with and without essential oil treatments.
Essential oils are recognized for their antimicrobial properties. Therefore, in this experiment, Gianfagna outfitted strawberry clamshell containers with sachets treated with oregano or thyme oil, known to control gray mold and other diseases. The project team harvested strawberries from four farms over the course of two-year’s worth of study.
The trials used about 20 berries placed in clamshells in MAP bags alone, outfitted with oregano or thyme oil sachets or a combination of essential oil sachets and MAP bags. Gianfagna and the team evaluated fruit quality based on weight loss over time, fruit firmness, sugar content (total soluble solids) and visible evidence of mold or disease.
Results indicated that modified atmosphere packaging, with or without essential oils, was most effective in maintaining postharvest quality; the team observed that MAP bags reduced the loss in fresh weight during cold storage for seven days in both years of the study for all farm harvests. Also, although not statistically significant across the entire study, a reduction in disease incidence was observed with the use of thyme and oregano oil sachets.
To address concerns about the potential for offflavors or aromas to berries caused by the essential oil sachets, Gianfagna also conducted consumer taste tests at farmers’ markets. Here, seven-day old stored fruit used in the trials were compared to freshly picked strawberries. While consumers preferred the freshly picked fruit, there was essentially no detection of herbal off-flavors or aromas with the stored berries.
Overall, the project showed promise that using MAP, especially in combination with essential oil sachets, can reduce disease incidence and maintain fruit quality. Results suggested that off-flavors and aromas should not be of concern to growers. Gianfagna said the next step for this research is to focus on partnering with a company to produce commercially available essential oil sachets. He was hopeful that farmers may use MAP and essential oil sachets, when commercially available, to extend the postharvest quality of fruits, vegetables and even cut flowers on their farms.