Bread bags from bread returns

Presented as part of Technology Transfer Seminars 2023

Returned bread and single use plastic bags are two major sustainability issues facing the industrial bread sector globally. Gert-Jan Moggre presented the results of the first stage of a research project he is part of, funded by BIRT and the Bioresource Processing Alliance, aiming to address these issues in a single solution by turning bread returns into bread packaging material.

In 2022 a total of 9,605 tonnes of bread return was collected in New Zealand, 74% of which was in the North Island, and 26% in the South Island. Most of the returns were loaf (86%). The majority of this is currently going to animal feed.

A compositional analysis showed that starch made up the bulk of the composition, with a larger variation in composition for mixed dried breadcrumb than white fine breadcrumb. Protein and insoluble fibre were identified as key components to try to control as their presence will affect the final properties of any new packaging material.

The project team developed and applied a method to extract starch from mixed dried breadcrumb (MDBC) and white fine breadcrumb (WFBC) starting materials with consistent composition (starch, protein and moisture), and which demonstrated consistent mechanical properties.

Three film casting experiments were carried out to test the options for creating material for packaging, first using bread thermoplastic starch (TPS) with no plasticiser, then bread TPS with plasticiser, and finally commercial TP with plasticiser.

They found differences in mechanical properties for the WFBC and MDBC in both rheological and film forming abilities, however thin-film composites could be formed from both the MDBC and WFBC when starch extract and supernatant were combined back in.

Tensile testing established that the more plasticity in the packaging, the more biodegradable it is, so there needs to be a balance between the bags being biodegradable and able to last long enough for good use.

The next steps in the project will be to test viability in commercial application by characterising material properties of TPS as a standardised, consistent polymer product, and carrying out a technoeconomic analysis to establish capital required, operating costs of proposed processes, and other factors that may affect profitability.

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