Denaturation of Soybean Protein by Freezing Part I

Abstract

When a solution of soybean acid-precipitated or IIS protein was frozen and stored at -1 to -5°C, the protein became partially insoluble after thawing. Ultracentrifugation and disc-electrophoresis of freeze-stored 11S protein solution after removing insoluble com-ponents revealed that new components which may be aggregates or associates of the I1S component were formed. When concentrated and stored at 5°C, disc-electrophoresis of 11S component showed that associates were formed. Mercaptoethanol could dissolve the insoluble protein and also convert the associates to the original 1IS component. NEM-IIS was not insolubilized by frozen storage at -5°C or storage at 5°C after being concentrated. From these facts it can be concluded that denaturation of soybean protein by freezing may be caused by intermolecular reactions through S-S bonds as a result of concentration by freezing. This may suggest a mechanism of the formation of sponge-like texture in kori-tofu which is made by frozen storage of soybean curd for 15 to 20 days at -1 to -3°C.