Processing residues used to create an active film for fresh food

Bio-based films offer a renewable and biodegradable alternative for modern food packaging, but these chitosan (CS) films often lack the mechanical strength, barrier performance, water resistance and active protection needed for demanding preservation conditions. Rapeseed production also generates cakes, stems, leaves and flowers rich in cellulose, polyphenols, flavonoids and other useful compounds, although much of this material remains underused.

Researchers from the School of Biological Engineering at Dalian Polytechnic University, working with INNOBIO Corporation Limited, have now addressed these challenges by turning underused rapeseed-processing residues into a biodegradable active film designed to protect fresh food.

The study, which has been published in Food Quality and Safety, said the material combines CS with phenolic extracts from processing residues of Brassica napus L., together with biosynthesised silver nanoparticles (AgNPs). This combination is designed to strengthen the film, improve resistance to water, oxygen and UV light, and adds antioxidant and antimicrobial activity.

Storage tests have been conducted using cherry tomatoes and enoki mushrooms — with the research evaluating whether the resulting films could combine structural durability, active preservation, food-contact promise and rapid environmental degradation in one packaging system.

The team prepared extracts from rapeseed cake, flowers, stems, and leaves, then used their plant compounds to reduce silver ions and form AgNPs averaging about 60 nanometres. The particles and extracts were blended into CS film-forming solutions and cast into composite films. Microscopy, FT-IR, XRD, and thermal analysis showed smooth, compact matrices with well-dispersed silver and no large crystalline aggregates.

The researchers also measured tensile behaviour, water resistance, light transmission, gas barriers, radical scavenging, bacterial inhibition, produce quality and soil degradation. Compared with pure CS, the researchers said the rapeseed-cake extract silver nanoparticle film increased tensile strength from about 8.1 to 17.0 MPa and raised elongation at break from 20.7 to 31.5%. Its water contact angle rose from 55.7 to 87.2°, indicating a less water-attracting surface. The flower-based film delivered the strongest antioxidant performance, reaching 89.7% scavenging in the DPPH assay and 62.3% in the ABTS assay. The rapeseed-cake film inhibited Escherichia coli and Staphylococcus aureus. Coated cherry tomatoes retained more weight, ascorbic acid and titratable acidity, while packaged enoki mushrooms showed less browning and microbial deterioration. The films fully degraded in soil within 21 days without significantly affecting bok choy growth.

By pairing rapeseed phenolics with biosynthesised AgNPs, the team created a film that is claimed to be stronger, less vulnerable to moisture and better able to slow oxidation and microbial growth. They said the produce trials are especially important because they move the concept beyond laboratory measurements and show how the material performs on highly perishable foods with different spoilage patterns and preservation needs.

The films could have potential for coatings, wraps or liners for fresh produce and other foods vulnerable to dehydration, oxidation, browning and microbial spoilage. Their use could also create new value streams for rapeseed-processing residues while reducing dependence on petroleum-based plastics.

More work is required before it is ready for commercial packaging applications. It will require scalable manufacturing, cost and sensory assessments, standardised food-contact testing and more trials under realistic transport and storage conditions.

Image credit: iStock.com/Photography By Tonelson