荔枝浊汁粗蛋白组分的结构和特性研究

The structure and characteristics of litchi cloudy juice protein fractions

采用Osborne分级法提取荔枝浊汁的上清液蛋白,沉淀中的球蛋白、醇蛋白和谷蛋白,对这4种蛋白进行了十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)、差示扫描量热法(DSC)和红外光谱分析,并测定了等电点(p I)、表面疏水性、总巯基和游离巯基及二硫键的含量。结果表明:4种蛋白的等电点在p H=4.0~4.5,上清液蛋白亚基分子量主要集中在(30~95)ku,谷蛋白(>270 ku);上清液蛋白、球蛋白、醇蛋白和谷蛋白的游离巯基含量分别占总巯基的71.86%、92.18%、58.82%、37.96%,且二硫键的含量均较低;上清液蛋白和醇蛋白均有2个变性峰,分别为88.0℃和129.5℃、40.5℃和92.3℃,而球蛋白和谷蛋白均只有一个变性峰,分别为103.0℃、85.3℃;4种蛋白的二级结构均以β-折叠和β-转角为主。综上所述,荔枝浊汁在热处理过程中上清液蛋白、醇蛋白和谷蛋白易变性,在贮藏过程中谷蛋白可能直接聚集,而其他几种蛋白可能逐渐变性而聚集。

Litchi cloudy juice and precipitation protein was divided into supernatant protein, globulin, gliadin and glutelin by Osborne classification method. We analyzed the four proteins by sodium dodecyl sulfate polyacrylamide gel electrophoresis （SDS-PAGE）, different scanning calorimetry （DSC）and infrared spectroscopy （IR）. Isoelectric point （pl）, surface hydrophobicity, total sulfhydryl group, free sulfhydryl group and S-S bond content were also determined. The results showed that their pl was about pH=4.0~4.5. The bands of supernatant protein were complex and mainly at （30~95）ku, while glutelin has the largest molecular weight （〉270 ku）. The free sulfhydryl groups of supernatant protein, globulin, gliadin and glutelin accounted for 71.86%, 92.18%, 58.82%, 37.96% of total sulfhydryl groups, respectively. The content of S-S bonds were low in these proteins. Two denaturation peaks, 88.00 ℃ and 129.5 ℃, 40.5 ℃ and 92.3 ℃, were observed in supernatant protein and gliadin, respectively; one denaturation peak, 103.0 ℃ and 85.3 ℃ were observed in globulin and glutelin, respectively. These proteins were β-sheet and β-turn. Taken together, supernatant protein, gliadin and glutelin were easy to denature during litchi cloudy juice thermization. Glutelin maybe aggregate directly during storage, while the other proteins maybe gradually denature and then aggregate.