适宜无机盐及浓度抑制麦胚脂肪酶存在时油水界面张力

为了探明无机盐稳定化脂肪酶的潜在机理,该文以小麦胚芽脂肪酶为研究对象,基于界面酶学的分析方法,研究添加浓度介于1.0×10-9~1.0×10-2 mol/L的Na~+、K+、Ca~(2+)、Mg~(2+)的氯化物对小麦胚芽脂肪酶存在的油-水界面特性的影响。结果表明,当小麦胚芽脂肪酶体系浓度为1.7×10-6 mol/L时,一价金属中Na~+更有利于抑制油-水界面的表面张力(P0.05),对麦胚脂肪酶存在时的油水界面特性影响也较大;二价金属离子Ca~(2+)对界面张力的影响趋势与一价离子不同,在高浓度时反而增加界面张力;当油水界面上存在脂肪酶的催化底物(三油酸甘油酯)和产物(油酸)时,添加浓度分别为10-6、10-6、10-4和10-9mol/L的Na~+、K~+、Ca~(2+)、Mg~(2+)均可一定程度上降低油水界面张力,从而降低麦胚脂肪酶的作用效果,三油酸甘油酯存在时Mg~(2+)的作用效果最明显(P0.05),油酸存在时Na+的作用效果最明显(P0.05)。综上,无机盐金属离子主要通过影响麦胚脂肪酶在油水界面的聚集行为及底物结构状态起到钝化麦胚脂肪酶的作用,该结果可为麦胚脂肪酶存在时界面的活性调控及麦胚的稳定化处理提供参考。

Suitable inorganic salt and its content inhibiting tension of oil-water interface with wheat germ lipase

Abstract: The stabilization of lipase is an important means to control the rancidity of highly oil-containing agricultural products, such as wheat germ. In this paper, the effects of different concentrations of Na+, K+, Ca2+ and Mg2+ on the oil-water interface characteristics of wheat germ lipase A (LA) were examined, based on the interfacial enzymatic analysis methods using interfacial tension meter and rotary rheometer. Firstly, the influence of the different concentrations of wheat germ LA on the interfacial tension of oil-water was studied to determine the concentration of LA system for the subsequent investigation about the effects of inorganic salts on the oil-water interface. Then, the interface tension and rheological properties of the oil-water after adding monovalent and divalent metal salt were studied to explore the effects of species and concentration on the oil-water interface. Next, the effects of different kinds of inorganic salts on the surface tension and rheological properties of oil-water interface, where there were lipase-acting substrate and product, namely, glycerol trioleate and oleic acid, were studied. Finally, the potential mechanism of inhibiting the catalytic activity of metal ions of inorganic salt in inhibiting wheat germ LA activity was discussed. The results showed that, when the concentration of LA was 1.70×10-6 mol/L, the monovalent metal ions Na+ and K+ were more favorable to decrease the interfacial activity of oil-water and the interfacial activity of wheat germ LA, than other divalent metal ions, i.e. Mg2+ and Ca2+. And the effect of Na+ was higher than that of K+. In the divalent metal ions, Ca2+ could decrease the interfacial tension at a low concentration and increase interfacial tension at a high concentration, while Mg2+ was opposite to Ca2+. At the same time, the decrease effect of Ca2+ on the interfacial tension was more obvious than Mg2+. Besides, the effects of glycerol trioleate and oleic acid on the interfacial properties of wheat germ LA were studied; the effect extent was glycerol trioleate > oleic acid, and the concentration of these 2 compounds was 1.0×10-5 and 5.0×10-6 mol/L, respectively. Under the 2 concentrations of glycerol trioleate and oleic acid, adding Na+ (10-6 mol/L), K+ (10-6 mol/L), Ca2+(10-4 mol/L), and Mg2+(10-9 mol/L)to the oil-water system, could reduce the interfacial tension of oil and water, and then reduce the effect of wheat germ lipase. In summary, inorganic salts play an important role in the inhibition of interfacial activity of wheat germ LA mainly by reducing the catalytic effect through affecting the aggregation behavior of wheat germ LA in oil-water interface and the structure of substrate, and play a role of passivating wheat germ LA. The results of this paper can provide theoretical support for the regulation of lipase activity and wheat germ stabilization in wheat germ industry.