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

Mycoprotein peptide hydrolysates have been used as starting materials for p lastein synthesis. Compared to other proteins studied, mycoprotein hydrolys ates were a relatively poor substrate for the plastein reaction and general ly led only to thixotropic viscous solutions, rather than to gelled product s, 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 sol ubilised by detergents such as sodium dodecyl sulphate although, like other s, it was largely solubilised by 50% (v/v) organic acids or 1 M NaOH and pa rtially 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. G el filtration failed to reveal any change in peptide molecular weight distr ibution 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 conditio ns used. Amino acid analysis revealed a marked preferential incorporation o f hydrophobic peptides into the plastein fraction. Differential scanning ca lorimetry results showed only broad peaks which suggested heterogeneous rea ction mixtures and products with no well-defined structural elements. These results are entirely consistent with plastein formation proceeding via a p urely physical aggregation pathway. (C) 2001 Elsevier Science Ltd. All righ ts reserved.