Lab protein coating developed from eggs by scientists from the Brown School of Engineering extended the shelf life of perishable fruits and vegetables. The researchers continue to refine the coating’s composition and are considering other source materials.

Did you know that eggs could be used as the base of an in expensive coating to protect fruits and vegetables? Lab tests on dip-coated strawberries, avocadoes, bananas, and other fruit showed they maintained their freshness far longer than uncoated produce. Compression tests showed coated fruit were significantly stiffer and more firm than uncoated and demonstrated the coating’s ability to keep water in the produce, slowing the ripening process.

The Brown School of Engineering lab of materials scientist Pulickel Ajayan and his colleagues have developed a micron-thick coating that solves problems both for the produce and its consumers, as well as for the environment. When the coating was applied to produce by spraying or dipping, it showed a remarkable ability to resist rotting for an extended period compared to standard coatings like wax but without some of the inherent problems.

The coating relied on eggs that never reached the market. The United States produces more than 7 billion eggs a year, and manufacturers reject 3 percent of them. The researchers estimated that more than 200 million eggs end up in landfills. “Reducing food shortages in ways that don’t involve genetic modification, inedible coatings or chemical additives is important for sustainable living,” Ajayan said. “The work is a remarkable combination of interdisciplinary efforts involving materials engineers, chemists and biotechnologists from multiple universities across the US.”

Along with being edible, the multifunctional coating retarded dehydration provided antimicrobial protection and was largely impermeable both to water vapor to retard dehydration and to gas to prevent premature ripening.

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Eggs that would otherwise be wasted can be used as the base of an inexpensive coating to protect fruits and vegetables, according to Rice University researchers.

Along with being edible, the multifunctional coating retarded dehydration provided antimicrobial protection and was largely impermeable both to water vapor to retard dehydration and to gas to prevent premature ripening. The protein coating was all-natural and washed off with water.

Egg whites (or albumen) and yolks account for nearly 70 percent of the coating. Most of the rest consists of nanoscale cellulose extracted from wood, which serves as a barrier to water and keeps produce from shriveling, a small amount of curcumin for its antimicrobial powers, and a splash of glycerol to add elasticity.

An analysis of freestanding films of the coating showed it to be highly flexible and able to resist cracking, allowing better protection of the produce. Tests of the film’s tensile properties showed it to be just as tough as other products, including synthetic films used in produce packaging. Further tests proved the coating to be nontoxic, and solubility tests showed a thicker-than-usual film is washable. Rinsing in water for a couple of minutes can completely disintegrate it, Ajayan said.

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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. Photos by Jeff Fitlow

The researchers continue to refine the protein 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 others,” said co-corresponding author Muhammad Rahman, a research scientist in Ajayan’s Rice lab, who mentored and led the team.

Ajayan is chair of Rice’s Department of Materials Science and Nano Engineering, the Benjamin M. and Mary Greenwood Anderson Professor in Engineering, and a professor of chemistry.

The Robert A. Welch Foundation and the Brazilian Ministry of Education’s Coordination for the Improvement of Higher Education Personnel program supported the research.