A micron-thick coating, made largely from leftover eggs, can extend the shelf life of your fruits and vegetables. By improving preservation times, the film supports efforts to reduce food waste.

The formulation, developed by a team at Rice University, won top honors in the Sustainable Technologies category of this year's "Create the Future" Design Contest  – an annual SAE Media Group competition that rewards the top technology inventions.

The coating has a unique combination of ingredients: egg whites and yolk, turmeric, plant-derived cellulose nanocrystals, and glycerol.

Impermeable to water and gases, the edible coating slows down dehydration and respiration, and provides antimicrobial protection. The egg-based film is all-natural and washes off with water.

Egg whites, or albumen, and yolks account for nearly 70 percent of the coating.

Nanoscale cellulose, extracted from wood, acts as a barrier to water and gases like oxygen and carbon dioxide. The shield holds water within the produce, slowing the ripening process and preventing shriveling.

A small amount of curcumin, the active compound in turmeric, provides antimicrobial protection.

Finally, a splash of glycerol adds elasticity.

Dip-coated strawberries, avocadoes, and bananas maintained their freshness far longer than uncoated produce, according to the team's tests. Compression analysis also demonstrated that coated fruits were significantly stiffer and more firm than uncoated food.

The researchers continue to refine the coating’s composition and are considering other source materials.

“We chose egg proteins because there are lots of eggs wasted, but it doesn’t mean we can’t use other [proteins],” said Muhammad M. Rahman in 2020 . Rahman, an assistant professor at Rice and the principal investigator of the project, mentored and led the team's formulation efforts.

In a Q&A with Tech Briefs below, Rahman explains more about why his team's coatings are so important to a world with so much spoiled food.

Tech Briefs: What are the ingredients of the coating, and what inspired you to go with egg whites?

Muhammad M. Rahman: Every year, more than 80 million metric tons of eggs are produced. And so, there can be a tremendous amount of waste generated along with the loss of various resources, including 53 gallons for a single egg. Along with their antimicrobial proteins acting as a natural protective barrier, egg whites are used due to their superior film-forming properties resulting from the organization of denatured proteins that allow it to be mechanically robust.

Tech Briefs: Is this coating easy to make?

Muhammad M. Rahman: The coating is very easy to make – we can make it in a couple of minutes.

Tech Briefs: What is it about eggs that supports preservation of foods?

Muhammad M. Rahman: The egg is used for its excellent film-formation capability with moderate gas barrier properties. The film matrix, formed by egg protein, allows for additional ingredients like turmeric to be accommodated, giving the film its antifungal and increased gas and water barrier properties that help to slow the ripening process.

Tech Briefs: How long does this coating extend the shelf life of products?

Muhammad M. Rahman: Our coating is capable of extending the shelf-life of fresh produce nearly twice as long. Currently, wax is the most common preservative/coating used for preservation, which is fat-based, but our healthier protein-based coating offers more versatility with increased efficacy compared to natural alternatives.

Tech Briefs: Where do you apply it, and how do you apply it?

Muhammad M. Rahman: The coating can be applied onto the surface of the fruits and vegetables via the most common two methods used in the industry – spray-coating and dip-coating.

A coating developed at Rice University made primarily with protein from eggs that would otherwise be wasted can be used to extend the freshness of produce. Photo by Jeff Fitlow

Tech Briefs: What needs to happen before this is used in a mainstream way? Do you think people are willing to put an egg-based coating on their fruit?

Muhammad M. Rahman: The coating demonstrated exceptional results for the first prototype, but we are looking to optimize its versatility and properties to cater to different application and consumer needs. For example, this coating is washable and so consumers who cannot or do not want to eat egg have a flexible choice – unlike today’s un-washable wax coating.

We are looking to substitute the egg protein with agro-protein components to address the needs of various diet and allergy preferences. The coating has proved successful at the benchtop scale, however, since the industry works at a larger scale, we are looking into conducting pilot scale studies (>1000 fruits/vegetables).

Finally, cost is always a concern when a technology hits the market. Our coating smartly utilizes low-cost, quality natural-food components that otherwise go to waste, and so the overall costs expected to be minimal. We look forward to confirming through an analysis on techno-economic feasibility.

Tech Briefs: Why is this coating so important?

Muhammad M. Rahman: Shockingly, 50% of fruits and vegetables – adding to the total $160 billion worth of food – are wasted every year due to damage and spoilage. Even just a 15% decrease in food waste could mean feeding 25 million people. Coatings are instrumental to reducing this waste via longer preservation. Moreover, existing commercial solutions for extending shelf-life of fresh produce involve primarily artificial wax coatings.

These non-washable petroleum-based coatings, however, present critical environmental and long-term environmental and long-term human health concerns, including disruption to the physiological balance and metabolism. This edible and washable protein-based coating offers a healthy and sustainable alternative to current coating options, thereby catering to the growing health-conscious consumer base.

The team included materials scientist Pulickel Ajayan, graduate student Neethu Pottackal, and undergraduate students Seohui (Sylvia) Jung and Yufei (Nancy) Cui.

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