Conformation Analysis of Soybean Protein in Reverse Micelles by Circular Dichroism Spectroscopy
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Conformation Analysis of Soybean Protein in Reverse Micelles by Circular Dichroism Spectroscopy Xiaoyan Zhao & Qiang Ao & Fangling Du & Qingjun Zhu
Received: 3 July 2010 / Accepted: 13 September 2010 / Published online: 25 September 2010 # Springer Science+Business Media, LLC 2010
Abstract Far-UV circular dichroism (CD) spectroscopy was used to study the conformation of protein from soybean flour under the influence of various reverse micelle environments and salt treatments, as compared with the protein using aqueous buffer extraction. These proteins exhibited characteristic CD spectra that reflected a considerable amount of residual secondary structures. The CD analysis showed that the protein modification by reverse micellar system was related to loss of α-helix and β-structure and increase of random coil. The ellipticity of protein in bis (2-ethylhexyl) sodium sulfosuccinate (AOT) and sodium dodecyl sulfate (SDS) reverse micelles was higher than in hexadecyl trimethyl ammonium bromide (CTAB) and TrionX-100. The CD spectra in reverse micelles except for SDS at 210 nm had lower intensity than in aqueous solution. Salts could influence the ellipticity of protein at near 194 nm in an order of NaCl>KNO3>>KCl>NaNO3 >Na2SO4 in monovalent salts and in MgCl2 >BaCl2 >CaCl2 divalent ones. Besides, the ellipticity was totally higher in monovalent salts than in divalent ones. Keywords Soybean flour . Reverse micelles . Salts . Soybean protein . CD spectra . Protein secondary structure X. Zhao : F. Du (*) : Q. Zhu Institute Agro-Food Science and Technology, Shandong Academy of Agricultural Sciences, No. 202, Gongyebei RoadJinan, Jinan 250100, China e-mail: [email protected] X. Zhao e-mail: [email protected] Q. Ao Institute of Neurological Disorders, Tsinghua University, Beijing 100049, China
Introduction Soybean proteins are applied in a wide range of food products as functional ingredients due to their high nutritional value, functional properties, and low cost. The method of protein isolation and processing will cause physicochemical changes on proteins and expand the range of protein functional properties. The soybean proteins contain four globulins, namely, 2S, 7S, 11S, and 15S proteins. These protein fractions are categorized by their sedimentation coefficients. The percentage content of 2S, 7S, 11S, and 15S was found to be 15%, 34%, 41.9%, and 9.1%, respectively (Fukushima 1991). The effect of general treatments on structural and functional properties of soybean proteins has widely been studied (Puppo et al. 2005; Wu et al. 2009). Adequate modifications on structure of soy proteins may well have different functional properties compared with the native proteins (Puppo et al. 2005; Mohamed 2002). Changes due to the difference in the extraction methods may alter the functional properties of the soy proteins, using physical (heat, high pressure, or mild alkali treatment), chemical (acylation, phosphorylation, and deamidation), and enzymatic extraction methods (Mohamed 2002; Li et al. 2007). Therefore, further funda
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