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This study focuses on protein alterations in fibrous meat substitutes produced by high moisture extrusion cooking of pea protein isolates. Three commercially available pea protein isolates and their respective extrudates were evaluated regarding their amino acid composition, molecular weight distribution and protein-protein interactions. Extrusion had no effect on the degree of hydrolysis and amino acid composition indicating that the thermal and mechanical energy during extrusion did not cause the formation of peptide bonds or the degradation of amino acids due to Maillard reactions. Decrease of protein solubilised from extrudates in a buffered solution containing urea indicated that the structural integrity of extrudates could be attributed mainly to covalent disulphide bonding and, to a smaller extent, to non-covalent interactions. Additionally, the disappearance of legumin bands in extrudates as determined by electrophoresis could be explained by its participation in a macromolecular network that was aggregated and cross-linked via disulphide bonds. This study contributes to a better understanding of the way the proteins interact during extrusion of pea protein isolates.

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The technofunctional properties of 2 protein isolates from Lupinus angustifolius L. Vitabor isolated by different procedures were investigated. The lupin protein isolate prepared by aqueous alkaline extraction with subsequent isoelectric precipitation (ILP) showed a significantly higher degree of protein denaturation and lower denaturation temperatures than the one obtained by aqueous salt-induced extraction followed by dilutive precipitation (MLP) as determined by differential scanning calorimetry. Rheological investigations revealed higher firmness and a viscoelastic solid-like behavior of ILP, in contrast to MLP that showed viscoelastic, liquid-like properties. Protein solubility of MLP was higher compared to ILP and solubility minima were slightly different for both lupin protein isolates. The protein isolates exhibited different technofunctional properties with ILP showing higher water binding capacity, lower oil binding capacity and lower emulsifying capacity than MLP. This reflects the different putative application of both lupin protein isolates as food ingredients, for example for ILP as a moisture enhancer and for MLP as a "natural" emulsifier in mixed food systems.

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