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Presented as part of Technology Transfer Seminars 2025
Dr Gert-Jan Moggré, Senior scientist, food chemistry and functionality at the institute of Plant & Food Research limited.
Solving two problems at once
Gert-Jan reported on the progress being made in the “Bread bags from Bread Returns” project which has now completed stage 2.
The project aims to address two major sustainability issues: returned bread, and single use plastic bags by asking what if we combined these two things? Can we make packaging out of bread returns using recovered starch turned into bread bag material that are compostable? The first step is to create starch thermoplastic. This behaves like a plastic and can be transparent but is fairly brittle and can attract water so it is blended with a second polymer to get the mechanical properties they need.
Stage 2 of the project is extruding and blending: ThermoPlastic Starch (TPS) by extrusion, blending with co-polymer, techno-economic modelling.
The team had to design an extraction process that is profitable and easy to do. They tried several processes. While there is higher starch recovery from white bread than mixed bread, they want to be able to use all bread returns. They have now confirmed they can make TPS using bread returns starch mixed with a polymer, with a range of tensile strength similar to commercial TPS based packaging materials.
A technoeconomic analysis came next, to consider if the concept makes financial sense. They needed to estimate the relative economic viability of the different processing options. Based on producing 220 million bread bags (the full requirement in New Zealand) they found that there are enough bread returns and that bags could be made at scale cost effectively based on their estimates, although on price alone they can’t compete with low density polyethylene bags. Consumer preference or legislation may require change to the use of these in future. The technoeconomic analysis for preparing TPS from returned bread found a net positive return in comparison to using commercial starch-based polymers made of virgin starch material.
Next steps are bread TPS production for bread bag applications including pilot-scale starch extraction, blow-forming bags with bread TPS/PBAT blends and testing functionalities key to the baking industry.
Further investigation is needed of the techno-economic analysis to settle on an optimum system and to increase the quality of the analysis assessment, involving unit operations user requirement specifications and quotations, variability testing, and setting feedstock and product specifications.