Distirbution, identification and amino acid composition analysis of proteins in the secondary precipitate of soy sauce

In this paper, proteins in the supernatant of soy sauce were used as control, and the secondary precipitate of soy sauce were prepared by static settlement-lyophilization.The molecular weight distribution, amino acid composition and average hydrophobicity of proteins in the secondary precipitate of soy sauce were investigated by N-TrisHydroxymethylMethylglycine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis ( Tricine- SDS- PAGE) and high- performance liquid chromatography ( HPLC) , then proteins in the secondary precipitate of soy sauce were identified by matrix- assisted laser desorption ionisation- time of flight /time of flight mass spectrometry ( MALDI- TOF/TOF MS) . Results showed that proteins with molecular weights of approximate22.7ku ( 80.20%, the basic polypeptide B3of soy glycinin G4) and 34.1ku ( 19.80%, the acidic polypeptide A1a of soy glycinin G1) were identified as the majority of proteins in the secondary precipitate of soy sauce. Furthermore, remarkable difference in amino acid compostion was observed between proteins in the supernant and the secondary precipitate of soy sauce, average hydrophobicity analysis showed that average hydrophobicity of proteins in the secondary precipitate was significantly higher than that in proteins of the supernatant. This work could contribute to the systematical knowledge of proteins in the secondary precipitate of soy sauce, and shed some light on its solving way.