酰化对芸豆分离蛋白热学特性的影响研究

Study on effect of acylation on thermal properties of kidney bean(Phaseolus vulgaris L.)protein isolate

从参与酰化反应基团的视角,运用热分析(DSC)技术,研究了不同酰化阶段芸豆分离蛋白热学性质的变化规律。芸豆分离蛋白(KPI)的酰化过程存在两个主要的酰化阶段,酸酐-蛋白比为0～0.1(乙酰化)和0～0.2(琥珀酰化)g/g,为ε-氨基(Lys)酰化阶段(N-酰化);再增加酸酐与蛋白比,ε-氨基酰化基本完成,反应进入羟基(Thr,Ser)酰化阶段(O-酰化)。在N-酰化阶段,琥珀酰化诱导KPI的热稳定性增加,而焓变(ΔH)略有降低,乙酰化不影响KPI的热稳定性和焓变(ΔH);羟基酰化阶段,酰化导致KPI变性温度(Td)降低,伴随焓变(ΔH)急剧下降。

The objective was to investigate the acylation-induced change in thermal properties of kidney bean protein isolate（KPI）by differential scanning calorimetry（DSC）techneques.The possible reactive amino groups of proteins,taking part in the acylation of KPI were explored.The relationships between thermal properties of acylated KPI and acylated stage were established.The data indicated that the acylation of KPI included two stages.One was the acylation of ε-amino groups（N-acylation）,the other was the acylation of hydroxyl groups（O-acylation）.In the N-acylation stage,the degree of the N-acylation sharply increased to about 93%～94% with the anhydride levels increasing from 0 to 0.1（acetylation）or 0.2g/g（succinylation）.The O-acylation（Thr,Ser）distinctly occurred only when the N-acylation was nearly completed.In the N-acylation case,succinylation led to the increases in the thermal stability,the decreases in the enthalpy changes（ΔH）,while the Td and the ΔH of KPI were unaffected by the acetylation.In the O-acylation case,the acylation led to the decreases in Td of KPI,accompanied with the sharp decrease in ΔH.