Plastic packaging currently presents a huge challenge to global sustainability, and with a 5% average growth per annum over recent decades, it shows no signs of slowing down. Plastic is the second most widely used material for food packaging, mostly for its low cost and ability to create a controlled environment for food storage and transportation – keeping food free from moisture, oxygen and microbes that would otherwise compromise its freshness or make it unsafe to eat.
There is a difficult balance to strike between prolonging the shelf life of food and minimising the resource use, weight, and complexity of packaging. Reduction of this packaging means more food waste, as it can no longer be kept in a controlled environment. This, in turn, worsens the carbon footprint and increases cost. Current packaging solutions often use multiple film layers which are bonded together, making recycling much more difficult than that of a single-material product like a plastic bottle.
The food packaging industry is therefore in pursuit of a new material that ticks all of the sustainability and regulatory boxes – biodegradable, food safe, and lightweight, with some even looking into incorporating active ingredients to keep food fresher and tastier than existing solutions. The HeTa Food Research Centre for Excellence of the University of Birmingham is investigating the use of starch to make a biodegradable, bio-sourced plastic to solve this issue, using yeast slurry - a waste product that would otherwise be disposed of in the brewing industry.
Figure 1: A flowchart showing the current process of producing the starch-based plastic.
As shown in Figure 1, a systematic approach will be employed for producing the starch-based packaging material from the yeast slurry waste product. The first step is to cultivate the waste yeast in a growth medium, adding bioactive compounds and enzymes. Yeast cells will then be mechanically disrupted by ultrasonication (using high-frequency sound waves to break large particles into smaller fragments) to release and harvest the polysaccharides (biopolymer). These are then extracted to form the basis of the overall bioplastic.
Purification methods are then applied to the solution to remove impurities and beer residues, followed by producing the film into thin layers plus multiple steps of drying at a controlled temperature, to form the final product. The product is then cut to size and appropriate conditioning and treatments are applied.
Post-processing analyses will be undertaken on the films to characterize them. These include microstructure analysis using scanning electron microscopy and physico-chemical assays (physical and chemical tests) to determine tensile strength, elasticity, deformity, density etc. Furthermore, the film will be optimised for improved performance, for example making the film less brittle. This is a common issue with many starch-based plastics, such as those made from algae. The aim of this process is to enable the yeast to produce a bioplastic that is both stronger and more flexible compared to existing alternatives. Finally, characterisation and testing are done to ensure the film meets the specifications and requirements to become packaging, as well as testing for biodegradability to ensure appropriate end-of-life pathways.
Future considerations
There are a variety of pros and cons which need to be considered when evaluating the efficacy of implementing such a system. A substantial amount of energy is used through multiple steps - cultivating, drying, and processing. Other issues include greenhouse gas emissions from these high energy requirements, the length of the process, which could increase cost, and the end-of-life route which could lead to a linear cradle-to-grave life cycle when ideally it would be circular (cradle-to-cradle). Additionally, the water usage is quite high as the yeast needs a growing medium for cultivation, however, this is a trade-off against many other bioplastics which require extensive land use for production to grow crops for their sugars. Utilising waste products is a particular strength of this method, as it doesn’t take away from potential food supplies or land that could be used for growing food.
Regulatory issues need to be considered, such as the migration of certain compounds between plastics and food. Approaches to infuse antimicrobial agents such as nisin (which is Generally Regarded as Safe (GRAS) for use in food within the film, will be explored in order to reach compliance with existing food safety regulations, as well as to increase the efficacy of the packaging material. This ultimately moves towards the goal of elongating the shelf-life of packaged foods. Evaluating factors such as these through future characterisation of the product is essential for the continuation of this line of research.
Further research
Future research includes Food Safety Research Network (FSRN) funding in order to determine the biodegradability of the product and take it from the proof-of-concept phase into a fully realised and industrially produced product. Future work aims to determine how long it takes to biodegrade, what the final products are, and where they end up. Ideally, end-of-life avenues would include a completely circular model; as the process begins and ends with waste, the material can be kept in circulation and out of landfills. In addition, there are avenues being investigated to recycle bioplastics (see our RePHASe spotlight).
In addition, to ensure circularity and appropriate end of life, an LCA (Life Cycle Analysis) needs to be conducted to account for the amount of energy and resources that need to be recovered for this waste recycling to be considered worthwhile. The process needs to be economically, socially, and environmentally sustainable, and more work must be undertaken to secure the data and justify that these criteria can be met. If the product cannot be made for cheaper than traditional plastic, or at least at a similar enough cost for it to make sense, then there will be a reliance on legislation to incentivise materials with more potential for circularity.
If you would like to find out more about this research, please contact Dr Helen Onyeaka, h.onyeaka@bham.ac.uk, or Dr Taghi Miri, t.miri@bham.ac.uk.