Novel uses of bio-polymers in composites : from chemistry to processing of materials and food

Abstract: Plant bio-polymers obtained as industrial side-streams (wheat gluten and potato proteins) and specifically designed potato starch and hemp fibres were used to produce composite materials. Fractionated pea protein and pea dietary fibres were used to make pasta-like sheets for production of healthy food. During processing of composite materials and food, the blend composition, temperature and additives influenced protein chemistry and structure and caused physicochemical changes. These physicochemical changes in proteins and other blend components, and their interactions, influenced the functional performance of materials and food. In wheat gluten protein-hemp fibre composites, the hemp fibres contributed to increasing stiffness, while higher temperatures increased protein cross-linking and thereby the mechanical strength of the composites. In wheat gluten protein-starch blends, high processing temperature (130 compared with 110 °C) induced a high degree of protein cross-linking and increased β-sheet formation, which increased both stiffness and strength in wheat gluten-starch blends and only strength in glutenin-starch blends. The gliadins showed a hierarchical hexagonal arrangement, observed for the first time in a gliadin-starch processed composite. The wheat gluten protein-starch composites also showed low oxygen permeability suitable for packaging applications. Combining glycerol with water improved composite processability and micro-structural morphology and also increased protein cross-linking and β-sheets. This increased the strength, stiffness and extensibility of wheat gluten- and glutenin-starch composites. Hot pressing at 130 °C induced a high degree of protein cross-linking and high amount of β-sheets and improved the mechanical properties of pea protein and pea protein-fibre at 90/10 and 80/20 blends. Pasta-like sheets with higher pea fibre content showed higher water uptake and reduced cooking losses. Chemical modification of wheat gluten and potato proteins de-polymerised the proteins, and thereby making them less cross-linked. In hot-pressed materials, less cross-linked proteins re-cross-linked and increased the tensile performance for potato proteins but not for wheat gluten. Processing conditions and blend component interactions in composites and foods governed the variation in protein cross-linking, structure and mechanical performance.