MTGase聚合酪蛋白酸钠生物聚合物的结构特征研究

采用紫外光谱、荧光光谱及红外光谱分析技术,研究了微生物转谷氨酰胺酶(MTGase)聚合酪蛋白酸钠(Na-CN)生物聚合物的空间结构特征,并探讨了MTGase改善Na-CN乳化性能的作用机理。紫外光谱显示,MTGase聚合Na-CN生物聚合物的多肽链的Trp和Tyr残基的紫外吸收峰的强度明显低于Na-CN,说明生物聚合物的“空间结构效应”占较重要的地位。荧光发射光谱显示,Na-CN生物聚合物的Trp和Tyr残基的荧光强度比Na-CN有显著的增强,表明生物聚合物的疏水性区域更加暴露。然而,MTGase长时间催化(12h)得到的生物聚合物的荧光强度反而有所下降(与4h的场合相比),这反映了“空间位阻效应”。红外光谱显示,Na-CN与其生物聚合物的酰胺特征峰相差不大,说明两者的二级结构基本上相近。此外,MTGase改善Na-CN乳化性能的机理是:MTGase催化导致Na-CN的空间结构发生了变化,进而改变了蛋白表面的表面疏水性质,最终达到改善Na-CN乳化性质的效果。

Studies on the Structural Features of Sodium Caseinate Biopolymers Polymerized by Microbial Transglutaminase (MTGase)

Steric structural features of sodium caseinate(Na-CN)biopolymers polymerized by MTGase were studied through UV-,fluorescence and IR-absorption spectrums,and mechanism of improving the emulsifying activity of Na-CN by MTGase was also investigated. The UV-absorption spectrum showed that the UV-absorption intensity of Trp and Tyr residues in peptides of Na-CN biopolymers was clearly lower than Na-CN,which suggested that'steric stractural effects'of biopolymers be responsible for the decline of UV-absorption. The fluorescence emission spectrum showed that the fluorescence intensities of Trp and Tyr residues in Na-CN biopolymers were strengthened markedly,compared to Na-CN,which indicated that the hydrophobic regions of biopolymers were more exposed. However,the fluorescence intensity of biopolymers obtained with longer incubation time(12 h)with MTGase declined,compared to those with 4 h,which reflected the'steric hindrance effects'. IR-absorption spectrum showed that there were nearly no differences in amide adsorption between Na-CN and its biopolymers, which mean both secondary structures were almost same. Moreover,the mechanism of improving the emulsifying activity of Na-CN by MTGase was discussed and pointed out as follows:MTGase polymerization resulted in changes of steric structures of Na-CN, then the surface hydrophobic properties of proteins were changed, which at last improved the emulsifying activity of Na-CN.