荔枝汁中谷蛋白结构及特性

Structure and Characteristics of Glutelin in Litchi Juice

采用Osborne分级法制备荔枝汁中的谷蛋白,并采用十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(sodium dodecyl sulfate-polyacrylamide gel electrophoresis,SDS-PAGE)、差示扫描量热仪、红外光谱等方法分析荔枝汁中谷蛋白的分子质量分布、热稳定性以及二级结构等。结果表明:荔枝谷蛋白分子质量较大,主要集中在50 k Da及以上,而且成分复杂,约有10个条带,经还原后,少量大分子质量条带消失,出现新的较小分子质量条带,其分子质量集中在50 k Da左右;用蛋白样品结合SDS的能力表征蛋白质的表面疏水特性,得出1 mg的荔枝谷蛋白样品结合(74.25±5.26)μg SDS;游离巯基含量为(29.83±1.72)μmol/g,总巯基含量为(40.59±2.04)μmol/g,二硫键含量为(5.38±0.18)μmol/g;荔枝谷蛋白的变性峰值为105.24℃;β-折叠和β-转角为荔枝汁谷蛋白主要结构,所占百分比分别为33.92%和64.7%。因此,可初步推断荔枝谷蛋白组分复杂,分子质量较大,具有较强的表面疏水性,二硫键含量较少,对热较稳定。

The glutelin from litchi juice was purified using the Osborne sequential protein extraction method,and its molecular mass distribution,thermal stability and secondary structures were analyzed using sodium dodecyl sulfatepolyacrylamide gel electrophoresis（SDS-PAGE）,differential scanning calorimetry（DSC） and infrared（IR） spectroscopy,respectively.The results showed that the glutelin had a large molecular mass and contained approximately 10 bands,most of which had a molecular mass of 50 k Da or above.After reduction,a few bands with higher molecular mass disappeared and new bands with smaller molecular mass（mostly including 50 k Da） appeared.The surface hydrophobicity was evaluated by SDS-binding capacity.The glutelin could bind（74.25 ± 5.26） μg of SDS per mg sample,and its contents of free sulphydryl group,total sulphydryl group and disulfide bond were（29.83 ± 1.72）,（40.59 ± 2.04） and（5.38 ± 0.18） μmol/g,respectively.Its denaturation peak temperature was 105.24 ℃.The major secondary structures were β-sheet and β-turn,accounting for 33.92% and 64.7%,respectively.Hence,we can infer preliminarily that the composition of glutelin in litch juice is complex,mainly containing high-molecular-weight glutelins,which have strong surface hydrophobicity,low disulfide bond content and good thermal stability.