Edible coating to keep strawberries fresh without refrigeration

University of British Columbia researchers have developed an edible, seaweed-derived coating that can help to keep strawberries fresh for at least four days at room temperature, outperforming uncoated berries stored in the fridge.

The solution is designed to help address food waste, with nearly half of all food produced being lost or wasted each year. Fresh fruits and vegetables are particularly vulnerable to spoilage, losing moisture and becoming susceptible to mould and bacteria during storage and transport.

Published in the Journal of Agricultural and Food Chemistry, the findings could help to provide a simple approach for extending produce shelf life and reducing reliance on refrigeration across the supply chain.

“We wanted to find a simple alternative to cold storage,” said senior author Dr Tianxi Yang, an assistant professor in UBC’s faculty of land and food systems. “Once we added the coating, the fruit became far less sensitive to changes in temperature and moisture and stayed fresh longer.”

UBC doctoral student Ivy Chiu (L) and UBC assistant professor Dr Tianxi Yang demonstrate their agar-based coating. Image credit: Clare Kiernan/UBC

The coating is made from agar, a substance derived from red seaweed that is widely used as a vegan alternative to gelatine and as a thickener in foods like puddings and jellies. On its own, agar forms a thick gel. But when researchers combined it with zinc, an essential nutrient, and tannic acid, a naturally occurring plant compound found in grapes and tea, the material transformed — self-assembling into tiny microparticles that create a thin protective layer around the fruit.

When dipped in the solution, strawberries, grapes and apple slices emerged with a thin, edible coating that dried completely clear.

“It was exciting to watch the particles self-assemble in real time, from a cloudy, milky liquid into this incredibly uniform, protective layer,” said doctoral student Ivy Chiu, the study’s lead author. “To our knowledge, no one had made an agar-based microparticle coating like this before.”

Over four days at room temperature, coated strawberries lost less than half as much water as uncoated fruit and remained noticeably firmer, with more vitamin C and antioxidants preserved. Grapes and apple slices showed similar benefits, with improvements lasting 14 days and 24 hours, respectively.

By comparison, untreated strawberries stored at room temperature began developing mould within two days, while refrigeration only extended their shelf life slightly — most untreated berries began to deteriorate by day four.

Coated strawberries stored without refrigeration remained mould-free for at least four days, while those stored in the fridge stayed fresh for at least six days.

The coating also showed antibacterial properties and no signs of toxicity in tests using human intestinal cells. For consumers who prefer to remove the coating before eating, most of it can be washed away with tap water within two minutes.

To assess its potential for real-world use, the team replaced laboratory-grade agar with commercially available food-grade agar. The results remained consistent, with coated strawberries showing reduced moisture loss and spoilage while maintaining quality.

“Our hope is to help keep produce fresh for longer throughout the food system,” Yang said. “If we can reduce spoilage during storage and transportation, we can reduce food waste while using less energy to preserve food.”

The research team is now testing the coating on additional fruits and vegetables and investigating how it could be scaled, tested and integrated into commercial food systems.

Top image credit: Clare Kiernan/UBC