霉变和辐照对大豆蛋白质理化性质和结构的影响

Effect of Mildew and γ-Irradiation on the Physicochemical Property and Structure of Soybean Proteins

摘要:

以新鲜大豆为原料制备了不同霉变程度的大豆，利用60Co-γ射线对大豆进行了辐照处理，采用胃蛋白酶体外消化率、氨基酸组分测定、SDS-PAGE电泳和傅里叶红外变换光谱（FT-IR）研究了霉变和辐照对大豆中蛋白质体外消化率以及蛋白质组成和结构的影响。研究表明：大豆培养30 d后，霉变导致大豆胃蛋白酶消化率降低23.74%，氨基酸总量减少2.07%，大豆蛋白质二级结构中的β-转角和无规卷曲分别增加了2.67%和4.17%，而α-螺旋和β-折叠相应减少3.62%和3.21%。在所考察的剂量范围内（10~30 kGy），辐照对新鲜大豆的胃蛋白酶体外消化率、氨基酸组成、蛋白质亚基组成没有显著影响（P>0.05），但对蛋白质二级结构中的α-螺旋与β-折叠具有显著影响（P<0.05）。霉变大豆经过γ射线辐照处理后，氨基酸总量降低，蛋白质二级结构中的α-螺旋与β-折叠减少，无规则卷曲增加。

Abstract:

Soybeans with different levels of mildew were prepared from fresh soybeans and then irradiated using cobalt-6060Co-γ rays. The effects of mildew and γ-irradiation on the in vitro digestibility, composition, and protein structure were investigated in terms of in vitro pepsin digestibility, amino acid composition, and results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) as well as Fourier transform infrared spectroscopy (FT-IR). The results indicated that mildew on soybeans reduced pepsin digestibility and total amino acid content by 23.74% and 2.07%, respectively, after 30 d culture. Moreover, the amount of β-turns and random coils increased by 2.67% and 4.14%, respectively, while the amount of α-helices and β-sheets decreased by 3.62% and 3.21%, respectively, in the secondary structure of soybean proteins. In fresh soybeans, γ irradiation had no significant effect (p > 0.05) on the amino acid composition, pepsin digestibility, and protein subunit composition within the dose range studied (10 to 30 kGy). However, a significant effect (p < 0.05) was observed on α-helices and β-sheets in the secondary structure of soybean proteins. On the other hand, in moldy soybean, γ irradiation resulted in a decrease in total amino acid content, a decrease in the amount of α-helices and β-sheets, as well as an increase in the amount of random coils in the secondary structure of soybean proteins.