Scientists have developed a biodegradable packaging film from rapeseed-processing leftovers, aiming to cut plastic use and extend the shelf life of fresh foods.

Published in Food Quality and Safety, the study was carried out by researchers at the School of Biological Engineering at Dalian Polytechnic University with INNOBIO Corporation.

The film is based on chitosan (CS) and includes phenolic compounds taken from rapeseed cake, flowers, stems and leaves.

The team also produced silver nanoparticles (AgNPs) from these plant extracts under mild conditions and incorporated them into the CS material.

According to the researchers, the resulting film was designed to combine mechanical strength, food preservation properties and rapid breakdown in soil.

Tests showed the extracts could reduce silver ions into nanoparticles of 60 nanometres. These particles were then mixed into film-forming solutions.

Compared with pure CS film, the version made with rapeseed-cake extract and silver nanoparticles showed tensile strength rising from 8.1MPa to 17.0MPa.

The water contact angle also rose from 55.7° to 87.2°, suggesting a lower attraction to water.

Among the different formulations, the flower-based film showed the highest antioxidant activity, recording 89.7% scavenging in the DPPH test and 62.3% in the ABTS test.

The rapeseed-cake version also inhibited Escherichia coli and Staphylococcus aureus.

In food storage trials, coated cherry tomatoes kept more weight, ascorbic acid and titratable acidity than untreated samples.

Enoki mushrooms packed with the films showed reduced browning and less microbial spoilage.

Soil burial tests found the films completely decomposed within 21 days and did not significantly affect bok choy growth.

The authors said the findings indicate that crop-processing residues may serve not only as raw material replacements but also as sources of useful chemical properties in packaging.

The films may be suitable for coatings, wraps or liners for fresh produce and other foods prone to dehydration, oxidation, browning and microbial decay.

They also noted that commercial use would still require larger-scale production methods, cost and sensory evaluation, standardised food-contact testing and trials under transport and storage conditions.

EDS detected no silver on tested tomatoes, though the study described this only as preliminary evidence.