Chinese scientists have developed an edible, washable protein-based coating that can extend the shelf life of fruit by 2½ times, by reducing moisture loss and microbial growth.
The low-cost coating was tested across 17 varieties of whole and cut fruits, including strawberry, tomato, kiwi and mango. It was shown to effectively delay rot by almost a week or more, at a cost of just 9 US cents per kilogram of fruit, according to a paper in the peer-reviewed journal Nature Communications.
The new strategy is as effective as existing preservation methods but reduces carbon dioxide emissions and the potential for toxicity, offering a promising solution to a major factor in global food waste.
“Addressing critical challenges in perishable fruit preservation ... we present an eco-friendly amyloid-like protein coating strategy developed through computer-aided molecular simulation,” the team led by researchers at Shaanxi Normal University said in their paper published on May 31.
“With edible properties, easy washability, and low cost, the coating demonstrates universal applicability for post-harvest and fresh-cut fruits.”
Around a third of all food produced globally is wasted, most of it perishable items like fruit and vegetables.
While all fruit have a natural protective barrier on their surface, harvesting renders them easily perishable due to dehydration, microbial growth, oxidation and ageing, thus limiting shelf life.
Strategies explored to extend the shelf life of fruit include genetic modification, wax coating, cold storage, and using “harmful” chemical preservatives such as formaldehyde.
While the waxing of fruit is widely adopted, there are concerns over the health implications of long-term consumption, due to the potential of wax to restrict oxygen and carbon dioxide exchange, according to the research team.
Meanwhile, cold storage may be more biosafe than some of the other methods, but it is expensive and energy-intensive, which adds to global carbon emissions.
Functional coating technologies using natural substances are a promising alternative, but developing a combination of materials that can evenly spread and adhere over the water-repellent fruit cuticle poses a challenge.
The researchers chose to use a phase-transitioned, amyloid-like protein, a type of material that is used to make underwater adhesives and stain-resistant fabric coatings.
Amyloid-like proteins are soluble and can be sprayed onto the surface of fruit. The researchers combined this with molecules of antimicrobial materials to make their coating.
“The superior performance of the amyloid-like protein coating stems from its enhanced spreadability, film formation, adhesion robustness and uniformity on fruit surfaces, which result in improved coating stability and prolonged preservation,” the team said in the paper.
“Our coating reduces carbon emissions by 90 per cent compared to standard refrigeration practices while extending shelf life by 2.5 times.”
The coating can delay fruit rot while achieving 60 to 98 per cent nutrient retention, which is more efficient than chemical preservation without the risk of toxicity, according to the paper.
While bare strawberries showed noticeable signs of decay after four days and severe fungal growth by day 10, the coated strawberries showed no apparent decay over this period.
The coating was able to extend the shelf life of cherry tomatoes from six to 16 days, kumquats from 15 to 30 days, and from two to eight days for both bananas and mangoes.
The material was also able to function under high temperatures, extending the shelf life of strawberries by three days under 42 degrees Celsius (107.6 degrees Fahrenheit).
While freshly cut uncoated apples showed bacterial presence on day two, the coated ones did not show such signs until day eight, indicating that the coating could delay browning and decay even on cut and peeled fruit.
“These findings underscore the universal fresh-keeping capability of the [coating] for fruit, doubling or even quintupling the typical shelf life of highly perishable fruits,” the team said.
Researchers from Tianjin University, Xinjiang Normal University, Changan University and the Second Affiliated Hospital of Xian Jiaotong University also took part in the study.
The biosafety of the coating was tested by feeding rats with spray-coated rat food. The animals exhibited no “distinct pathological alterations” and their blood, kidney and liver function tests were normal.
“The biocompatible, edible, and easily washable nature of the [amyloid-like protein] coating provides a practical and safer alternative for food preservation,” the team asserted.
-- SOUTH CHINA MORNING POST
