薄壳山核桃仁的蛋白质组成及其内源性 蛋白酶活性Protein components and activity of endogenous proteases in pecan kernels

Abstract

为了对薄壳山核桃仁中的主要蛋白质，特别是相对丰度较低的功能活性蛋白进行系统研究，以新鲜的薄壳山核桃仁为原料，利用电泳、液相串联质谱和氨基酸分析等方法，考察了薄壳山核桃仁的主要蛋白质和功能活性蛋白（抗氧化酶、内源性蛋白酶），并对内源性蛋白酶的最适pH和温度进行了研究。结果显示：薄壳山核桃仁的主要蛋白质包括11S球蛋白（58%）、7S球蛋白（17%）和9 kDa蛋白（15%），还含有0.239%超氧化物歧化酶、0.190%过氧化氢酶和0.282%内源性蛋白酶；只检测到1种蛋白酶抑制剂，并且其相对丰度极低；内源性蛋白酶在pH 3.5~5.5和40~60 ℃时可发挥水解活性，并在pH 4.5和50 ℃时活性最强；在氨基酸组成方面，薄壳山核桃仁蛋白的赖氨酸含量低（3.74%），但谷氨酸+谷氨酰胺含量（19.51%）和精氨酸含量（14.12%）高。说明国产薄壳山核桃适宜鲜食，对促进人体健康有益。 In order to systematically examine the major proteins in pecan kernels, especially the bioactive proteins with low relative abundance, the major proteins and bioactive proteins(antioxidant enzymes, endogenous proteases) in fresh pecan kernels were investigated by tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis, liquid chromatography tandem mass spectrometry and amino acid analysis.The optimum pH and temperature of the endogenous proteases were also studied. The results showed that the major proteins in pecan kernels included 11S globulins (58%), 7S globulins (17%) and 9 kDa proteins (15%), as well as 0.239% superoxide dismutases, 0.190% catalases and 0.282% endogenous proteases. Only one protease inhibitor was detected, and its relative abundance was extremely low. These endogenous proteases showed hydrolytic activity at pH 3.5-5.5 and 40-60 ℃, and optimal at pH 4.5 and 50 ℃. As for the amino acid composition, the proteins in pecan kernels contained a low content of lysine (3.74%), but a high content of glutamic acid + glutamine (19.51%) and arginine (14.12%). It is suggested that domestic pecans are suitable for fresh consumption, which is benifical for promoting human health.

Keywords

• 薄壳山核桃仁；蛋白质；抗氧化酶；内源性蛋白酶
• pecan kernel; protein; antioxidant enzymes; endogenous proteases