FTIR spectra studies on the secondary structures of 7S and 11S globulins from soybean proteins using AOT reverse micellar extraction

Fourier transform infrared (FTIR) method was used to study the secondary structures of 7S and 11S globulins from soybean proteins using aqueous buffer and reverse micelles extraction method for the first time. The Fourier second derivative was applied to all spectra, revealing that the amideband of 7S and 11S globulins with two extraction methods consisted of eight bands. The I band frequencies were assigned to α-helix, β-sheet, unordered and turn structure. The second derivative spectra of 7S and 11S globulins had been shifted with reverse micellar extraction method compared with their spectra with aqueous buffer extraction method. The relative amount of different structure of 7S and 11S globulins could be estimated through accurate measurement of the band intensities. The results indicated that the percentage of 7S globulin α-helix and β-sheet, turn structures decreased with the reverse micelles extraction (7S globulin: 14.5% α-helix, 45.6% β-sheet, 14.4% unordered, 23.8% turn; 11S globulin: 17.0% α-helix, 47.3% β-sheet, 16.5% unordered, 19.3% turn), compared with 7S (16.5% α-helix, 47.6% β-sheet, 35.9% turn) and 11S (17.0% α-helix, 47.3% β-sheet, 35.8% turn) globulins by the aqueous buffer extraction, while the percentage of 11S globulin α-helix and β-sheet structures did not change. The percentage of unordered structure was 14.4 and 16.5, respectively. The amount change of these substructures might affect functional properties of 7S and 11S globulins.