采用FTIR技术研究高压处理对冻干大豆分离蛋白构象的影响

采用傅里叶转换红外光谱技术(FTIR)研究了高压(HP)处理对冷冻干燥的大豆分离蛋白(SPI)构象的影响。在SPI的去卷积FTIR光谱的酰胺Ⅰ′区域(1 600～1 700 cm-1)，观察到12个与蛋白构象相关的红外吸收峰，分别对应于CO键伸缩振动与肽键的C—N伸缩振动。通过对该区域的峰强度与波数分析显示，压力为200～400 MPa的HP处理导致SPI在该区域的峰发生明显的“红移”(约2 cm-1)，强度也显著增加。更高的HP处理进一步增强了SPI的酰胺Ⅰ′区域的峰强度。对酰胺Ⅱ峰分析显示，HP处理导致酰胺Ⅱ峰(如1 560～1 500 cm-1)的强度、面积逐渐增加(与压力呈正相关)。以上分析显示，HP处理导致SPI的二级与三级结构逐渐打开，然而变性蛋白的结构在高压释放后经历一个“重构过程”。

Effects of High Pressure on the Conformation of Freeze-Dried Soy Protein Isolate:A FTIR Spectroscopic Study

The effect of high pressure (HP)treatment on the conformation of freeze-dried soy protein isolates (SPI)was investigated by Fourier transform infrared (FTIR) spectroscopy. Within the amide Ⅰ′ region (1 600-1 700 cm-1)of the deconvoluted FTIR curve of SPI, more than 10 bands associated with protein conformation were distinctly observed, attributed to the CO stretching vibration and to a small extent to C—N stretching vibration of the peptide bonds, respectively. The secondary structure of native SPI is estimated to be composed of 15%-16% α-helix, 39%-44% extended strands, 17.5% random coils, and 21%-27% turns. The analyses of intensity and wavenumber of the bands showed that, HP treatment at pressures of 200-400 MPa resulted in the increases in intensity and a “red-shift” (about 2 cm-1)of these bands. HP treatment at 600 MPa further increased the band intensity of the amide Ⅰ′ region. The analyses of amide Ⅱ bands showed that HP treatment led to gradual increases in intensity and absolute area of amide Ⅱ bands, in a pressure-dependent manner. Thus, it is suggested that HP treatment resulted in gradual unfolding of secondary and tertiary structure of SPI, while the structure of denatured proteins underwent a “rebuilding” process after the release of high pressure. These results confirm that the HP-induced modification of SPI is by means of the HP-induced conformational changes.