Our team have been developing new and novel materials for packaging with a focus on antimicrobial films for extended shelf-life of food products. In recent years, the emphasis has shifted towards bio-based and biodegradable polymers. Some examples of our research in this area are provided below.
Incorporation of essential oil extracts into LDPE film to impart antimicrobial activity:
The extracts studied include thymol, carvacrol, and linalool which are obtained from plant species such as thyme, basil and oregano. The levels of the extracts were varied and were also tested in combination. As suite of physico-mechanical and antimicrobial inhibitory tests were performed to optimise the formulations.
Inhibition of S. aureus by extruded LDPE films with and without thymol.
Starch-based films coated with antimicrobial agents for extended shelf-life of cheese:
In this work, thermoplastic starch films were prepared using different levels of carvacrol, thymol and linalool. Physico-mechanical, migration and inhibitory tests were conducted, and the films were also tested using cheese samples.
Example of mould inhibition of carvacrol coated starch film (upper image) and significant mould growth when carvacrol was not coated on the film (lower image).
Polylactic acid/kenaf fibre composites containing thymol:
In this work, PLA composites were formed by combining natural plant fibres and essential oil extract thymol which imparted both antimicrobial activity and a plasticizing effect. The prepared composites were optimised for the best overall composition and were shown to inhibit fungal growth on processed chicken with 40 wt% kenaf and 10 wt% thymol.
Inhibition of mould growth on processed chicken is evident after 24 days when the PLA/kenaf composite contains thymol.
Microencapsulation of thymol in beta-cyclodextrin for controlled release from LDPE film:
One of the challenges using essential oil extracts is their volatility during high temperature processing required to produce films. This work optimised the encapsulation of thymol in BCD to both protect thymol from loss during processing, and to enable its controlled release. The films produced were effective in extending the shelf-life of ground beef.
Influence of ethanol content on the encapsulation efficiency of thymol in BCD showing that <10% ethanol is optimal (left image). Molecular representation (right image) of BCD in the centre, thymol, ethanol, and water molecules.
Semi-refined carrageenan films for packaging applications:
Seaweed extracts such as carrageenan can be easily formed into biodegradable films. This work used a semi-refined carrageenan which is less expensive than the more refined type. Films were prepared and optimised based on levels of plasticiser, the addition of nanocellulose and nanoclay, coating with polycaprolactone, and crosslinking agent.
Addition of nanocellulose fibrils (NCF) into semi-refined carrageenan (SRC) and refined carrageenan (RC). The trends show the influence of NCF on various properties related to hydrophilicity with the SRC generally more hydrophilic than RC. The inclusion of NCF into both types slightly improving the moisture and barrier properties.
Have investigated ethylene vinyl alcohol (EVOH) films incorporated with green tea and oregano extracts, and red beet extracts; polypropylene/polyethylene terephthalate laminated films impregnated with olive leaf extract; and hydroxypropyl methyl cellulose films containing PLA/green tea extract nanoparticles.