Interaction of Wax, Fungicide and Ethylene Treatments on Storage and Shelf-Life of Satsuma Mandarins

Abstract

Satsuma mandarins (Citrus unshiu Marc.) were once the center of an important industry along the Gulf Coast of the United States. Several freezes in the early 1900’s essentially wiped out the industry. In recent years there has been renewed interest in development of the industry. Currently little is known about the optimal postharvest practices for these small delicate fruit. Without improved knowledge of postharvest practices, the industry will not be able to expand into new markets, such as retail stores. Retail stores require fruit to be of a specific external quality, namely, orange, blemish free fruit with a turgid appearance. Since Satsumas can reach maturity prior to obtaining the required orange peel color, fruit often need to be degreened with an exogenous application of ethylene. Fungicides can be used to prevent disease related blemishes, while the use of wax may allow fruit to keep their turgid appearance for longer periods.

In order to identify the most efficient means of providing fruit that meet retail store specifications, a postharvest study was initiated to determine the best combination of degreening, waxing and treating with fungicides for both storage and shelf-life. Fruit were assigned to one of twelve treatments with combinations of ethylene (ethylene or no ethylene), wax (waxed or no wax), and fungicide (Imazalil, 2-(4-thiazolyl) benzimidazole, or no fungicide). Fruit with an ethylene treatment were exposed to 5ppm of ethylene for 24 hours at room temperature. Both external peel (color and amount of disease) and internal quality (Brix, titratable acidity, and Vitamin C) measures were taken for each treatment. Treating fruit at 5ppm of ethylene for 24 hours at room temperature had only a minor effect in promoting color development. Waxing the fruit had the greatest effect on preserving fruit quality, especially size and weight. Fungicide had a minor effect on preserving fruit quality, in part because disease incidence was low. In future studies, the impact of ethylene on internal quality needs to be monitored with respect to taste. Waxing also had a detrimental effect on Vitamin C in both years of the study. Higher rates of ethylene, higher temperatures, or longer exposure time to ethylene are most likely needed to achieve acceptable degreening. In a pilot study, fruit were exposed to higher concentrations of ethylene in order to determine if a higher rate of ethylene provides better color development. Results of the pilot study indicates that higher levels of ethylene and storage at room temperature provide for better color development compared to storage in a cold environment or no ethylene. Future research needs to identify the proper application rate of ethylene that promotes color development while minimizing fruit damage from excessive amounts of ethylene.