热杀菌期间胰蛋白酶改性对蛋清液耐热性和结构特性的影响

Effect of Trypsin Modification on Heat Resistance and Structural Properties of Liquid Egg White during Heat Sterilization

为提高蛋清液的巴氏杀菌温度,开发具有较高耐热性的蛋清液,探究胰蛋白酶改性对蛋清液耐热性和结构特性的影响。本研究设置未改性组和酶改性组,以25℃蛋清液为对照,4种不同热杀菌温度为实验组(56、62、68℃和72℃处理3 min),采用浊度和上清液蛋白含量2个指标衡量蛋清液耐热性的变化,利用表观黏度、粒径、表面疏水性、傅里叶变换红外光谱、十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(sodium dodecyl sulfate-polyacrylamide gel electrophoresis,SDS-PAGE)和扫描电子显微镜(scanning electron microscope,SEM)等对蛋清蛋白结构进行表征。胰蛋白酶改性能显著降低蛋清液浊度,提高上清液的蛋白含量(P<0.05)。随着热杀菌温度提高,蛋清液的浊度逐渐增加,上清液蛋白含量逐渐减少,粒子大小也逐渐增大。在相同热杀菌温度时,与未改性蛋清液相比,酶改性蛋清液的浊度和表观黏度显著降低,同时表面疏水性显著升高(P<0.05),粒径分布接近正态分布。酶改性可抑制蛋白热聚集,改善耐热性。SEM结果显示酶改性使蛋清蛋白表面孔隙增多,颗粒更加分散,在同一热杀菌温度时,表面保留的颗粒数量明显多于未改性蛋清。SDS-PAGE分析显示酶改性后蛋清中大分子蛋白发生降解。傅里叶变换红外光谱显示,在低于68℃条件时,酶改性蛋清液α-螺旋结构的相对含量显著高于未改性蛋清液(P<0.05),无规卷曲结构相对含量明显低于未改性蛋清液。综合分析,胰蛋白酶可有效改善热杀菌过程中蛋清蛋白热聚集,提高蛋清液的耐热性,对扩大其销售半径有重要意义。

In order to increase the pasteurization temperature and heat resistance of liquid egg white,the effect of trypsin modification on the heat resistance and structural properties of liquid egg white was investigated in this study.The sample in this study consisted of two groups:unmodified and enzyme-modified.Each group was kept at 25℃(control)or sterilized at 56,62,68 or 72℃for 3 min.The changes of heat resistance were measured by turbidity and supernatant protein content,and the structure of egg white protein was characterized by apparent viscosity,particle size,surface hydrophobicity,Fourier transform infrared(FTIR)spectroscopy,sodium dodecyl sulfate-polyacrylamide gel electrophoresis(SDS-PAGE),and scanning electron microscopy(SEM).Trypsin modification significantly reduced egg white turbidity and increased the protein content of the supernatant(P<0.05).As the sterilization temperature increased,the turbidity and particle size of egg white gradually increased,while the protein content of the supernatant gradually decreased.At the same sterilization temperature,the turbidity and apparent viscosity of the modified egg white were significantly lower,while the surface hydrophobicity was significantly higher(P<0.05)and the particle size distribution was closer to the normal distribution compared with that of the unmodified egg white.Enzymatic modification could inhibit protein thermal aggregation and improve heat resistance.SEM results showed that enzymatic modification increased the surface porosity of egg white protein and the dispersity of the particles;at the same sterilization temperature the number of particles retained on the surface was higher in modified than in unmodified egg white.SDS-PAGE analysis showed that enzymatic modification promoted the degradation of large molecular mass proteins in egg white.Fourier transform infrared spectroscopy showed that at temperatures below 68℃,the relative content ofα-helix of the modified egg white was significantly higher than that of the unmodified egg white(P<0.05),while the relative content of random coil was significantly lower than that of the unmodified egg white.In conclusion,trypsin can effectively improve the thermal aggregation of egg white proteins during heat sterilization and improve the heat resistance of liquid egg white,which is important for expanding its sales radius.