超声预处理对大豆蛋白聚集体结构和乳化特性的影响

以大豆分离蛋白为原料,采用超声对蛋白进行预处理,经加热(100℃、20 min)和离心得到可溶性热聚集体(STSPI),以可溶性大豆分离蛋白(SSPI)(原大豆分离蛋白溶于磷酸盐缓冲液后离心制备)作为对照,探究热诱导对超声预处理蛋白的结构特性(微观结构、粒径分布、官能团、二三级结构、电位、疏水性)和乳化特性(乳化性和乳化稳定性)的影响。结果表明:与STSPI相比,超声预处理再经加热、离心后得到的可溶性蛋白(USTSPI)在超声时间和超声功率为6 min、600 W时,其平均粒径、电位绝对值、蛋白质分散度指数(PDI)和浊度分别下降了273.50 nm、6 mV、0.33和288.2;官能团中羰基和二硫键质量摩尔浓度分别降低了0.26 nmol/mg和0.38μmol/g,游离氨基和游离巯基质量摩尔浓度提高了0.16μmol/mg和0.59μmol/g;α-螺旋和β-转角结构增多,β1结构相对含量降低了11.97个百分点;表面疏水性指数提高了364.78,乳化性指数和乳化稳定性指数提高了123.56 m2/g和360.95 min。这说明对蛋白进行超声预处理后能在一定程度上阻碍因热效应导致的蛋白乳化活性降低,可为解决因加热引起蛋白乳化特性降低问题提供参考。

Effect of Ultrasonic Pretreatment on Structure and Functional Properties of Soy Protein Aggregates

The protein was pretreated with soy protein isolate(0,6 min 200 W,6 min 400 W,6 min 600 W,12 min 600 W and 24 min 600 W),then heated(100℃,20 min),centrifuged and dried to prepare soluble thermal aggregate.Aggregates,using ultrasound-free pretreatment of soluble soy protein isolate(original soy protein isolate was dissolved in phosphate buffer and prepared by centrifugation)as a control,to investigate the structural characteristics(spatial structure,particle size distribution,functional group,potential,hydrophobicity)and emulsifying properties(emulsification and effect of emulsion stability).The results showed that compared with SSPI,USTSPI reached the maximum in the ultrasonic time and ultrasonic power of 6 min,600 W,and the average particle size,absolute value of potential,protein dispersity index(PDI)and turbidity were decreased by 273.50 nm,6 mV,0.33 and 288.2,respectively.The carbonyl and disulfide bonds in the functional group were reduced by 0.26 nmol/mg and 0.38μmol/g,respectively,and the free amino and free sulfhydryl groups were increased by 0.16μmol/mg and 0.59μmol/g.Theβ-turn structure was increased,theβ1 folded structure content was decreased by 11.97 percentage points;the surface hydrophobicity was increased by 364.78,and the emulsification and emulsion stability were increased by 123.56 m2/g and 360.95 min,respectively.The above results indicated that the thermal aggregates can change the protein structure to reduce the emulsification properties of the protein,while the ultrasonic pretreatment can resist the degradation of protein emulsification activity caused by thermal effects to some extent,which provided a method for solving the problem of protein emulsification degradation caused by heating.