酸法脱酰胺改善大米蛋白的溶解性及其功能性质分析

Improvement of Solubility of Rice Protein by Acid Deamidation and Analysis of Functional Properties

大米蛋白是一种优质的植物蛋白,但较低的溶解特性限制了大米蛋白的应用范围,为提高大米蛋白的溶解性,该研究采用酸法脱酰胺对其进行改性处理,处理条件为料液比1∶25(g/mL)加入0.4 mol/L HCl溶液,95℃水浴加热搅拌4 h,分析改性前后蛋白的溶解性、起泡及起泡稳定性、乳化及乳化稳定性、表面疏水性、持水性、持油性等功能性质,以及亚基分子量、表面微观结构的变化。结果表明,酸法脱酰胺处理改善大米蛋白溶解性效果显著,中性环境(pH7)中由0.58%提高至56.60%,碱性环境(pH值为12、13)溶解性达到90.00%以上。pH值为3、7时起泡性、乳化性改善效果较好,起泡性分别由22.50%、80.40%提高至78.50%、151.70%,乳化性分别由4.4、6.6 m^(2)/g提高至14.3、16.5 m^(2)/g,过度的水解也会导致表面疏水性的降低,进一步影响界面性质的改善效果。酸法脱酰胺改性对蛋白质的持水性、持油性改善效果不明显。改性后蛋白亚基分子量大幅度降低,主要分布在6.5~20 kDa之间,有序的β-折叠结构转变成无序的无规则卷曲结构,蛋白微观结构由聚集变得松散,致密的球状结构变为不规则块状结构,表面由粗糙变得光滑。

Rice protein is a high-quality plant protein,but its low solubility limits its applications.In the present study,acid deamidation was employed to improve the solubility of rice protein.The treatment conditions were as follows:0.4 mol/L HCl solution was added at a liquid-to-solid ratio of 1∶25(g/mL),followed by heating and stirring in a water bath at 95℃ for 4 h.The functional properties such as solubility,foaming,foaming stability,emulsification,emulsification stability,surface hydrophobicity,water and oil holding capacity,and the changes of subunit molecular weight and surface microstructure were analyzed before and after modification.The results showed that the acid deamidation treatment significantly improved the solubility of rice protein.The solubility increased from 0.58% to 56.60% in a neutral environment(pH7)and exceeded 90.00% in an alkaline environment(pH12 and pH13).The foaming and emulsification properties were notably improved at the pH values of 3 and 7.The foaming properties increased from 22.50% to 80.40% and from 78.50% to 151.70%,respectively,and the emulsification properties increased from 4.4 m^(2)/g to 14.3 m^(2)/g and from 6.6 m^(2)/g to 16.5 m^(2)/g,respectively.Excessive hydrolysis led to reduced surface hydrophobicity,which further affected the improvement in interface properties.The acid deamidation modification had a less noticeable effect on water and oil retention of protein.After modification,the molecular weight of protein subunits dramatically reduced,mainly distributed between 6.5 and 20 kDa.The ordered β-sheet structure transformed into an unordered irregular coil structure.The protein microstructure transitioned from aggregation to looseness,the dense spherical structure changed to irregular block structure,and the surface changed from rough to smooth.