Isolation, Identification and Amino Acid Composition of Proteins in Soy Sauce Residue
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Abstract:
In this paper, the soy sauce residue was prepared by filtration-lyophilization, and the supernatant of soy sauce was used as control. The proximate indices of soy sauce residue were comparatively analyzed. The molecular weight distribution, variety and source and characteristics of amino acid composition of proteins in soy sauce residue and the supernatant were investigated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), matrix-assisted laser desorption ionisation-time of flight/time of flight mass spectrometry (MALDI-TOF/TOF MS) and high-performance liquid chromatography (HPLC). Results showed that soy sauce residue (wet) was mainly composed of carbohydrate (15.98%), proteins (10.19%), NaCl (10.10%) and water (59.50%). Analysis of SDS-PAGE and MALDI-TOF/TOF MS results demonstrated that proteins in soy sauce residue primary consisted of molecular weights of 19.3 kDa (a, 59.40%), 31.8 kDa (b, 12.91%) and 12.3 kDa (c, 27.69%) subunits, and proteins with molecular weights of 19.3 kDa (a) was identified as the basic polypeptide B3 of soy glycinin G4. Research on amino acid composition indicated the hydrophobic amino acid content and the average hydrophobicity of proteins in soy sauce residue were significantly higher than those in the supernatant proteins. The differences were the chief characteristics in amino acid composition of proteins in soy sauce residue, and could explain the low solubility and formation of soy sauce residue proteins.
