“The most significant property challenge that is solved is achieving antimicrobial properties, low oxygen permeability, and low water vapor permeability simultaneously with a coating of biological origin that is edible, easily washable, and exhibits sufficient adhesion and good ripening retardant properties”Muhammad M Rahman
Researchers at Rice University have developed a protein coating that can extend the shelf life of perishable products such as fruit and vegetables. The micron-thick egg-based coating is also edible, prevents dehydration, offers antimicrobial protection and is mostly impermeable to water vapor and so retards dehydration, and gas, preventing premature ripening in fresh produce.
It is thought that about 3% of all eggs end up in landfills, while a third of food produced is also wasted. As described in Advanced Materials [Jung et al. Adv. Mater. (2020) DOI: 10.1002/adma.201908291], when the team applied the natural coating, either by spraying or dipping, it was able to stop produce from rotting for a longer time than conventional coatings while also avoiding some of the problems these can cause.
Standard methods for food preservation have their own health and environmental concerns, involving genetically modified produce, refrigeration, chemical additives, or inedible wax coating, all of which are either expensive, energy consuming, or not very good for you. About two-thirds of the new coating in this more environmentally friendly method is made from yolks and egg whites, with the remainder being nanoscale cellulose extracted from wood that acts as a barrier to water and helps keep produce from shriveling, and small amounts of curcumin and glycerol.
On testing fruits that were dip-coated, they were found to keep their freshness much longer than uncoated produce. Compression tests also demonstrated that coated fruit were substantially stiffer and firmer, and retained water in the produce, slowing down ripening. As team leader Muhammad M Rahman told Materials Today, “The most significant property challenge that is solved is achieving antimicrobial properties, low oxygen permeability, and low water vapor permeability simultaneously with a coating of biological origin that is edible, easily washable, and exhibits sufficient adhesion and good ripening retardant properties”.
This multifunctional green composite material could be used as post-harvest preservative coating for farms and a commercial product to extend freshness for consumers, as well as to prolong food storage. As it uses materials that can be sourced from waste, the approach is a possible low-cost solution to the problem of world hunger.
The team are looking to further refine the composition of their coating and are exploring source materials such as proteins extracted from plants rather than animal produce, including corn or soy protein to make them suitable for vegans or those with egg allergies. Other coating methods could also be assessed, including atomizing spray coating systems.