The Effect Mechanism Of Microwave And Inorganic Salts On Wheat Germ Lipase

Wheat germ(WG) is "the natural treasure-house of human nutrition", however, because of its endogenous enzymes, it incline to get rancidity and deteriorated rapidly, which leading to the resources can not be fully used. Microwave treatment is one of the effective methods to inactivate wheat germ lipase, however, the mechanism of wheat germ stabilization by microwave has not been confirmed yet. Meanwhile, in view of the important effect of inorganic salts on the lipase structure and activity, wheat germ and its endogenous enzymes were used as the research objects, supplemented with inorganic salts, and the characteristics of wheat germ dielectric and interfacial tension and interfacial rheology of oil-water interface as the hydrolytic site of wheat germ lipase, respectively. The aim of the study was to reveal the mechanism of microwave cooperated inorganic salt on the inactivation of in wheat germ lipase.The main research contents and results are summarized as follows:1. The network analyzer and coaxial probe technology were used to study the dielectric properties of WG under different conditions. The results showed that wheat germs ε’ at frequencies of 915 MHz were slightly larger than those at 2450 MHz, but ε″ at 2450 MHz was significantly larger than that at 915 MHz, WG had a better thermal conversion ability at microwave frequency of 2450 MHz than that at 915 MHz. WG dielectric properties increased with the increase of water content, when the water content increased from 4% to 16%, the ε’ and ε " increased from 2.61 and 0.02 to 4.32 and 0.8, respectively. The increase of WG water content could significantly increase the dielectric properties of WG, and enhance the WG stabilization effect to a certain extent; The dielectric properties of WG with 5 kinds of inorganic salt added showed that NaCl had a significant effect on ε’ and ε", and the effect was most obvious when the mass fraction of NaCl was 1%.2. The interfacial activity of wheat germ lipase(LA) was investigated by interfacial tension meter and rotary rheometer. The results showed that the interfacial tension and tanδ decreased with the increase of wheat germ LA concentration, and when the concentration of wheat germ LA exceeded 1.7×10-6 mol/L, the interfacial tension was unstable. The interfacial characteristics were most obvious at the range of 1.7×10-6 mol/L in the range of LA concentration of wheat germ. The effects of glycerol trioleate, glycerol monooleate and oleic acid on the interfacial properties were studied.The effect extent of them on wheat germ LA interfacial activity was: glycerol trioleate> glyceryl monooleate> oleic acid, And the concentration of the three compounds was 1.0×10-5 mol/L, 1.0×10-5 mol/L and 5.0×10-6 mol/L, respectively.While in the presence of triolein, the effect of glycerol monooleate and oleic acid on the interfacial properties can be further verified.3. The effect of inorganic salt ions on wheat germ LA interfacial activity of wheat germ was studied by interfacial tension meter and rotary rheometer. The results showed that the interfacial tension changed regularly while the interfacial rheological parameters changed inregularly. Na+ and K+ increased the oil-water interfacial tension, and the maximum value was respectively 21.078 mN/m and 20.835 mN/m at the concentration of 1.00×10-5 mol/L and 1.00×10-6 mol/L respectively. The effect of Na+ is stronger than that of K+, that is, Na+ is more effective in inhibition of the wheat germ LA interfacial activity; Ca2+ could decrease interfacial tension at low concentration and increase interfacial tension at high concentration, while Mg2+ was opposite to Ca2+, could increase interfacial tension at low concentration. At the same time, the decrease effect of Ca2+ on interfacial tension was more obvious than Mg2+.4. The effects of inorganic salt ions on lipase interfacial activity of wheat germ under different interface conditions were studied using interfacial tension meter and rotary rheometer. The results showed that the interfacial tension of the control group and Na+ group was similar in the temperature range of 25 ℃-45 ℃, and the interfacial tension was the highest at 30 ℃, which showed that Na+ had the best inhibition on wheat germ LA interfacial activity at 30 ℃. The interfacial tension of K+, Ca2+ and Mg2+ groups was similar at 25 ℃-45 ℃, and reached the maximum at 45 ℃. The temperature effect was the most obvious on Ca2+ group. The influence of temperature on the interfacial rheological properties was mainly influenced by G’’, and the variation of G’’ and tanδ were consistent with the variation of interfacial tension. The results also showed that the addition of inorganic salts with different types and concentrations reduced the interfacial tension of oil and water in the presence of glycerol trioleate or oleic acid, and the effect of Na+ on G’ and G’’ was the most obvious while the changes of tanδ were inregular.