79-2 |
|
C. D. MEJIA, Food Science Department, Purdue University, 745 Agriculture Mall Drive, West Lafayette, IN 47907-2009, L. J. Mauer, Dept. of Food Science, Purdue Univ., 745 Agriculture Mall Dr., West Lafayette, IN 47907-2009, and B. R. Hamaker, Whistler Center for Carbohydrate Research, Purdue Univ., Dept. of Food Science, 745 Agriculture Mall Dr., West Lafayette, IN 47907-2009. Glycinin is the major seed storage protein of soybeans. The foaming and emulsifying properties of this protein in its native state were shown to be limited due to its globular structure, which is characterized by a low surface hydrophobicity and a limited molecular flexibility, thus significant efforts have been done to modify this protein. Partial dissociation of glycinin, achieved by changes in pH or ionic strength, has been proven to cause an enhancement of the surface behavior and functionality of the protein. However, the connection between these properties and changes in the secondary structure of glycinin has not been fully determined. Our objective was to analyze the changes in the secondary structure of glycinin caused by select ionic strength and pH conditions relevant for food products using Fourier-transform infrared (FTIR) spectroscopy. Glycinin was extracted and purified using centrifugation and isoelectric precipitation. The isolated glycinin was then dialyzed at 20°C against potassium phosphate buffers at pH of 7.6, 5.3 and 3.8 and ionic strength of 0.5, 0.2 and 0.03. ATR-FTIR spectra of the buffers with and without glycinin were collected using 256 scans, 4 cm-1 resolution, and a ZnSe ATR cell. PeakFit software was used to quantify secondary structure of glycinin from deconvoluted spectra. Results showed that at pH 7.6 and ionic strength 0.5, glycinin presented a greater proportion of b-sheet as compared with the solutions at lower ionic strength. However, when glycinin was in solution at pH 5.3 and 3.8 the opposite trend occurred. This alteration in glycinin secondary structure might explain the beneficial effect of dissociation on the functionality of this protein. Thus, modifications of its secondary structure will change its interfacial properties.
Session 79, Food Chemistry: Protein and enzyme chemistry
|