Improving shelf life of blueberries with upcycled edible coating

A team of chemical engineers from UNSW Sydney are turning what was once waste into a protective film that could help extend the expiry date of Australia’s delicate summer fruits — such as blueberries, which are known to perish quickly. 

As described in the journal Food and Bioprocess Technology, the researchers have developed an edible film made from coffee waste that could help preserve the freshness of delicate fruits by reducing how much water seeps in or out. The new formulation was created and tested in their lab, making sure it could be applied directly to food. The next step is to test this as a coating in real-life environments, before scaling it up to commercial production.

By upcycling spent coffee grounds, the research offers a two-for-one environmental win: reducing food-industry waste while creating a biodegradable product. Preliminary tests also suggest the oil-containing films could help inhibit bacterial growth on the film’s surface. This opens the door to a further antimicrobial function.

“We’ve created a polysaccharide-based coating to improve the fruit’s water-vapour barrier,” said UNSW lead author and PhD candidate Lilah Saidi.

“The coating contains cellulose nanofibres (CNFs) — derived from used coffee grounds — and grapeseed oil.”

Current polysaccharide films made from other plant cellulose fibres or starches are already widely studied for use as edible coatings because they are biocompatible, biodegradable and food-safe. But they are not effective at protecting fresh produce from moisture.

“Polysaccharides are excellent biopolymers for films, but their major disadvantage is their high water affinity,” Saidi said.

“Our innovation lies in repurposing spent coffee grounds. These are an abundant waste product from cafes that can serve as both nano-fillers and stabilisers in the coating.”

Saidi said nanofibres from the coffee grounds help create a tighter, more interconnected network, making it harder for water molecules to migrate through. The grapeseed oil, being water-repellent, further reduces the film’s affinity for moisture.

“This leads to a food film that is still clear and see-through while also having an improved mechanical strength. The nanofibres from coffee grounds make it tougher and more flexible — and are also safe to eat.”

Saidi said the new formulation provides a gentle, edible ‘skin’ in the form of a spray coating or a packaging film that preserves freshness, reducing the reliance on synthetic plastics.

“These properties are especially well-suited to barrier coatings, potentially slowing dehydration, or moisture absorption, in those more highly perishable fruits like blueberries.”

Challenges ahead

Professor Cordelia Selomulya, Saidi’s PhD supervisor, said while the research is helping improve polysaccharide-based films, turning this innovation into a solution for large-scale commercial fruit production remains a challenge.

“Translating laboratory films into a commercially viable fruit coating is no easy process,” Selomulya said.

This means testing the coating on fruit beyond the lab under real-world storage and transport conditions, while exploring application methods and regulatory approvals.

The team’s next study will investigate a new source of cellulose nanofibres that can be produced differently and offers further unique properties — paving the way for even more advanced and versatile coatings.

For now, they’ve filed a provisional patent for this discovery and are open to collaborations with commercial fruit producers.

Image credit: iStock.com/mtreasure