Application of the plastein reaction to mycoprotein: II. Plastein properties

Mycoprotein peptide hydrolysates have been used as starting materials for plastein synthesis. Compared to other proteins studied, mycoprotein hydrolysates were a relatively poor substrate for the plastein reaction and generally led only to thixotropic viscous solutions, rather than to gelled products, and only low yields of insoluble plastein material. Once formed, however, the insoluble fraction remained insoluble over the whole pH range of 2–11. In contrast to many other plasteins, the mycoprotein material was not solubilised by detergents such as sodium dodecyl sulphate although, like others, it was largely solubilised by 50% (v/v) organic acids or 1 M NaOH and partially solubilised by chaotropic agents such as 8 M urea, 6 M guanidinium chloride and 7 M potassium thiocyanate. A combination of 8 M urea and 50% (w/v) citric acid completely solubilised the plastein to a clear solution. Gel filtration failed to reveal any change in peptide molecular weight distribution on plastein formation while ion-exchange chromotography showed some quantitative differences but these were difficult to interpret as most of the material did not adhere to the anion-exchange column under the conditions used. Amino acid analysis revealed a marked preferential incorporation of hydrophobic peptides into the plastein fraction. Differential scanning calorimetry results showed only broad peaks which suggested heterogeneous reaction mixtures and products with no well-defined structural elements. These results are entirely consistent with plastein formation proceeding via a purely physical aggregation pathway.