复合酶法改性制备乳清分离蛋白可溶性聚合物的性质

Properties of Soluble Aggregates Prepared from Whey Protein Isolate Modified by Mixed Enzymes

为探究胰凝乳蛋白酶与谷氨酰胺转氨酶(transglutaminase,TGase)复合酶法改性制备乳清分离蛋白(whey protein isolate,WPI)可溶性聚合物的性质,本实验利用电泳、荧光分光光度计和旋转流变仪等对可溶性聚合物的性质进行对比分析。结果表明:复合酶改性制得的聚合物与单一TGase改性相比,黏度增大,游离巯基含量显著降低,但表面疏水性和ζ-电位无显著变化。复合酶改性聚合物平均粒径是(153.66±9.15)μm,而TGase改性聚合物平均粒径是(157.92±10.91)μm,没有显著差异。通过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳和非变性聚丙烯酰胺凝胶电泳对比分析得出,单独的TGase改性聚合物分子质量较大,被截留在凝胶加样口,而复合酶改性聚合物分子质量更多的集中在65 k D附近,即聚合物分子大小适中,这与粒径的结果相呼应。胰凝乳蛋白酶和TGase复合改性聚合物表面呈波纹片状,结构均一紧致。与未改性的WPI相比,复合酶改性WPI聚合物pH值溶解性曲线在pH 2.0~7.0范围变化较平缓,且在pH 4.0~5.0时溶解性提高。此研究结果为复合酶法改性WPI在酸乳或酸性乳饮料方面的应用提供了理论依据与技术参考。

This study was aimed to explore the properties of soluble aggregates from whey protein isolate(WPI)modified with mixed chymotrypsin and transglutaminase(TGase)using electrophoresis,a fluorescence spectrophotometer and a rotational rheometer.The results showed that the viscosity of protein aggregates modified by mixed enzymes was higher,and the content of free sulfhydryl groups was significantly decreased;however,the surface hydrophobicity andζ-potential did not change significantly when compared with single TGase modification.The average particle size of mixed enzymemodified aggregates was(153.66±9.15)μm,while that of TGase-modified aggregates was(157.92±10.91)μm,suggesting no significant difference.Comparative analysis using SDS-PAGE and Native-PAGE showed that single TGase-modified aggregates had higher molecular weight,and was trapped at the injection port;in contrast,the molecular weight of aggregates modified by mixed enzymes was moderate,mostly distributed around65kD,which was coincided with the particle size distribution.The surface of aggregates modified by both enzymes showed a corrugated shape with structural uniformity.The solubility curve of mixed enzyme-modified WPI aggregates in the range of pH2.0-7.0was gentle,while the solubility was increased at pH4.0-5.0when compared with the unmodified whey protein.The results in this study may provide a theoretical basis and technical reference for applying enzymatically modified WPI in yogurt and fermented dairy beverage.