Edible coating more than doubles strawberry shelf life

A new edible coating is based on pectin, pullulan and chitosan(Credit: Shutterstock)

Strawberries may be delicious, but they don't have much of a shelf life. So if you find a great bargain on a flat of them, you can end up throwing half of it away after a few days. In a move that may save many a shortcake, scientists at the University San Nicolás de los Garza in Mexico have developed an edible coating made from pectin that preserves strawberries for longer without affecting their taste.

According to the Food and Agriculture Organization of the United Nations, over 4.5 million tons (4 million tonnes) of strawberries are cultivated each year, with the main producers in the United States, Turkey, Spain, Egypt, and Mexico. The trouble is that, though the plants are tough, the soft fruits are very perishable, susceptible to bruising, and require a lot of special care. During harvest time, the fields need picking every three days and the fruit needs to be rushed from the field and cooled down with fans.

For shipping fresh strawberries, the fruit must be quickly and carefully cooled to 32° F (0° C), which is cold enough to preserve them, but just warm enough to prevent ice crystals from turning them into mush. Even then, the shipping containers must be specially packed to keep the temperature stable while preventing the fruit boxes from coming into contact with walls, floors, or ceilings of the transport. Even then, the last leg from market to dinner table is something of a sprint.

The team's answer to this situation was to create an Edible Active Coating (EAC) designed to improve the quality and extend the shelf life of strawberries. The coating is based on pectin, which is a constituent of many fruit and vegetable cell walls. This was combined with chitosan, which is an antifungal compound derived from crustacean shells and the key ingredient in a spray-on coating for bananas, pullulan for extracellular support, and sodium benzoate and potassium sorbate.

The strawberries were washed and disinfected, then dipped into the coating before being packed and stored at a temperature of 39.2° F (4° C). The team found that compared to a control group of strawberries, the coating preserved, or even improved, the color, flavor, and texture of the fruit. The strawberries with the coating lost less weight, remained firmer, retained their peak color longer, and had their shelf life increased from six to 15 days. In addition, the coating protected the strawberries longer from microbial growths, and the acidity was unaffected.

According to the team, the coating is suitable for industrial-scale application on post-harvest strawberries.

The team's results were published in the Journal of Food Science.

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