热加工对豆乳蛋白质溶解性和脲素酶活性的影响

本文研究不同热加工处理对豆乳蛋白质的影响,采用传统热煮浆、微波煮浆、加压高温煮浆对豆乳蛋白质氮溶解指数(nitrogen soluble index,NSI)和脲素酶活性的影响,同时对不同热加工处理的豆乳蛋白进行表面疏水性、自由巯基和透射电镜分析。结果表明:在90℃煮浆15 min的传统热煮浆条件下,蛋白质的NSI值为81.62%±1.07%;在650 W微波煮浆40 s条件下,NSI值为75.35%±0.65%;在100℃加压高温煮浆3 min,NSI值为91.31%±1.50%,均显著高于生豆乳的NSI值(69.03%±0.82%)。传统热煮浆、微波煮浆、加压高温煮浆三种热处理方式均可以降低脲素酶活性。通过对蛋白质自由巯基、表面疏水性和透射电镜观察分析,传统热煮浆、微波煮浆、加压高温煮浆与生豆乳相比,三种热处理方式均使蛋白质自由巯基含量显著降低(p<0.05);表面疏水性显著升高(p<0.05);豆乳体系油滴与蛋白共溶、分散性更好。由此可见,不同热加工处理的豆乳蛋白质的溶解性提高是通过深层改变蛋白的结构来实现的。 

Effect of different heating process on the protein solubility and urease activity of proteins in soymilk

In order to explore the effect on protein characteristics of soymilk by heating processes including traditional heating, microwave heating and high temperature with pressure heating, the protein NSI value, urease activity, surface hydrophobicity, free sulfhydryl and transmission electron microscope were studied. The results showed that, compared with the NSI value of protein of raw soymilk was 69.03% ± 0.82%, the NSI value of protein was 81.62% ± 1.07% by traditional heating at 90 ℃ for15 min.After microwave heating, the NSI value of protein was 75.35% ± 0.65% at 650 W for 40 s.The NSI value of protein of high temperature with pressure heating was 91.31% ± 1.5% at 100 ℃ for 3 min.Urease activity was inhibited by the processing of traditional heating, microwave heating, high temperature with pressure heating.Compared with raw soymilk, the free sulfhydryl content of protein was remarkably declined by traditional heating, microwave heating and high temperature with pressure heating ( p < 0.05) , but the surface hydrophobicity of protein was remarkably higher ( p < 0.05) , respectively. The microscopic structure analysis of the soymilk showed that soymilk protein and oil droplets cosolvent had uniform distribution and better dispersion.Thus, the improvement of protein solubility of soymilk after different heating processes was achieved by the deep change of protein structure.