Application of the plastein reaction to mycoprotein: I. Plastein synthesis

The plastein reaction has been applied for the first time to mycoprotein following in situ digestion of crude material to solubilise protein and produce the required initial peptide mixture. Pepsin was found to be superior to the other proteinases tested (trypsin, chymotrypsin, papain, Streptomyces griseus proteinase) in the plastein synthesis step although in all cases yields of insoluble plastein were low (10–15%). Unusually, plastein yield was not much influenced by pH over the range 3.0–7.5, but percentage yield increased almost linearly over the peptide concentration range 11–43% (w/w) while the absolute yield of plastein increased exponentially over this range. Incubation at different temperatures showed that the rate of plastein formation was highest at 65°C, reaching a maximum in 4–5 h but, although not reaching maximum yield for 24 h, a temperature of 37°C gave approximately 25% greater yield. In general terms, the results suggested that mycoprotein peptides represented a rather poor substrate for plastein synthesis and only opaque, viscous solutions were obtained rather than the more common thixotropic gel structures.