Towards Pea Protein and Pea Fibre Fortified Low Moisture Extrusion of Starch for the Manufacture of Expanded Extrudates

This work addresses the increasing demand for expanded snacks and cereal ingredients rich in protein and fibre and free of major allergens. Heat and shear induced structural changes of pea protein and how pea protein and pea fibre fortification af-fects the final product characteristics after low moisture extrusion were hence investigated. To separate the effect of heat and shear treatment on pea protein, a detailed study using capillary rheometry was carried out. Heat treatment resulted in the formation of shear sensitive aggregates, as identified via FTIR and SDS-PAGE, which reduced the water solubility. The longest heat treatment time affected the vicilin and convicilin subunits of the protein. When pea protein isolate was exposed to varying shear and heat stresses during low moisture extrusion, the vicilin and con-vicilin subunits were not affected. Similar to the capillary rheometry trials, however, protein aggregates were formed. Direct expanded extrudates with a sectional expansion index of up to 13 could be obtained at a specific mechanical energy input above 180 kJ/kg and a product temperature above 130°C. Further, investigation of the extrusion process of more complex blends, rice starch fortified with up to 42% pea protein and up to 24% pea fibre, showed a significant influence of the feed composition on the final product characteristics. At intermediate contents of protein (25%) and fibre (16%), enhanced expansion compared to rice starch occurred, while considerably less expanded extrudates were obtained at greater protein and fibre contents. This was likely caused by the protein and starch alignment in thin layers in the cell walls, which also resulted in disrupted surface morphologies as shown by light and scanning electron microscopy. µ-CT imaging identified that the addition of fibre resulted in increased air cell densities and, depending on the protein content, additionally in thicker or thinner cell walls at 10% and 42% protein or 0% and 25% protein, respectively. In a fourth step, based on the previous results, a blend was selected for scale-up trials from pilot to commercial scale extru-sion, resulting in the successful production of expanded extrudates with 42% protein and 16% fibre at an industrial manufacturing site