Helping avocados stay fresh with a coating of chitosan-derived solution.

Avocado always seems to be popular when it’s smashed on toast, creamed with guacamole, or mixed into salad dressing. However, the fruits are notoriously hard to bear, turning from pale green to brown and mushy in the blink of an eye. Now, researchers in ACS Food Science and Technology Report a chitosan-based coating that preserves them for longer periods. The team also developed imaging technology to quickly predict their shelf life.

To see if an avocado is ripe, most people squeeze it gently, and a little sponginess indicates that it is ripe. Producers conduct similar assessments to determine which avocado variety can handle transportation to grocery stores. Despite these tests, some of them spoil prematurely.

Therefore, researchers have developed techniques to delay ripening, using compounds such as 1-methyl-cyclopropene (1-MCP). More recently, studies have shown that naturally derived chitosan—a prebiotic derived from the exoskeletons of oysters—confers antimicrobial activity when used as a coating on fruits, including avocados. Therefore, Angie Homes Jara, Angelica Sandoval Aldana, and colleagues wanted to compare the effectiveness of the two preservation methods on avocado quality and shelf life.

The researchers treated commercially ripe Hass avocados with either a gaseous solution of 1-MCP or aqueous solutions containing various concentrations of chitosan. Mimicking real-life transportation conditions, processed and unprocessed avocados were refrigerated at 41 degrees Fahrenheit for 21 days and then brought to room temperature to simulate a grocery store environment, until they rotted.

Untreated samples that were treated with either 1-MCP or 1% chitosan were at optimal ripening for 6 days. Fruits treated with a coating of 1.5% chitosan were the best for 12 days. However, these samples also had uneven hardness once they matured, as well as green and purple spots in the shell, which the researchers say shows that chitosan coatings could be improved in the future.

Throughout the study, the researchers also imaged the entire surface of the fruits with hyperspectral cameras in the visible and near infrared spectrum. The reflectance data from the images was then compared with the avocado’s firmness, skin color, oxygen consumption, and weight loss using a number of computer models.

Two machine learning models explained the changes that occurred during the ripening of avocados and could predict the remaining shelf life. Researchers say that a chitosan-based coating and prediction technology can help improve the shelf life and quality of avocados for sale.