Strawberries can remain presentable for several days at room temperature thanks to an almost invisible protective layer made partly with agar.
This substance derived from algae is already widely used in food. The new coating slows water loss and fruit deterioration without requiring permanent refrigeration.
A fresh strawberry quickly loses water after being picked. Its fragile surface also makes it vulnerable to damage and the growth of microorganisms. Cold slows these processes, but storing and transporting refrigerated food requires a great deal of energy.
Strawberries placed on a white table
Unsplash illustration
The scientists therefore designed a barrier that is deposited directly on the fruit. Its base is agar, a gelling material extracted from algae. They combined it with tiny particles formed through the interaction between zinc and tannic acid, a plant substance belonging to the polyphenol family.
Once applied, these particles assemble to form a continuous protective film.
This layer reduces exchanges with the environment. Treated strawberries lose less moisture, retain their firmness better and resist deterioration more effectively. Tests also involved grapes and apple pieces, with improved preservation of several characteristics related to their freshness.
The coating also has antibacterial activity measured in the laboratory. Tests conducted on cultured human intestinal cells showed no toxicity under the conditions studied. Much of the layer can also be removed by briefly rinsing it with water, making it easier to use on foods eaten directly.
The process was designed to go beyond the laboratory. The scientists obtained results using commercially available food-grade agar. This matters when considering larger-scale production, because it avoids relying on a rare or specially manufactured material.
The aim is not necessarily to eliminate cold storage everywhere. Such a film could mainly limit losses when refrigeration is difficult, costly or interrupted between harvesting and consumption. Very fragile fruits are particularly concerned, since a short period at room temperature can accelerate their deterioration.
The researchers also assessed the environmental impact of their process. Their analysis found that the coating had a lower carbon footprint and lower toxicity to freshwater environments than conventional refrigeration-based storage of strawberries.
The next step will be to confirm this performance on a large scale, under real storage and distribution conditions.