利用核磁共振研究脂肪氧合酶酶促氧化蛋黄磷脂

Lipoxygenase-Catalyzed Oxidation of Egg Yolk Phospholipids Studied by Nuclear Magnetic Resonance Spectroscopy

利用^(31)P核磁共振比较酶促氧化前后蛋黄磷脂的组成,通过^(1)H核磁共振监测并比较空白组(未氧化)与脂肪氧合酶酶促氧化及95℃水浴加热氧化过程中脂肪酰基的相对物质的量、一级和二级氧化化合物含量的变化。结果表明:磷脂酰胆碱和磷脂酰乙醇胺是蛋黄磷脂的主要成分;蛋黄磷脂氧化后,磷脂酰胆碱和磷脂酰乙醇胺含量均下降,而溶血性磷脂含量增加;所有被氧化的蛋黄磷脂样品中总不饱和脂肪酸相对物质的量均下降,而饱和脂肪酸相对物质的量均上升;其中在pH 6酶促条件下,亚油酸降解速率最快。脂肪氧合酶在pH 6条件下催化氧化蛋黄磷脂生成更多的氢过氧化物,加热后主要生成(Z,E)-2,4-二烯醛;而在pH 9条件下蛋黄磷脂生成氢过氧化物后快速降解,在加热后生成较多正构烷醛。因此,可以利用脂肪氧合酶在pH 6条件下催化氧化蛋黄磷脂生成更多的2,4-二烯醛类风味化合物。

^(31)P nuclear magnetic resonance(NMR)spectroscopy was used to compare the composition of egg yolk phospholipids before and after enzymatic oxidation.^(1)H NMR spectroscopy was used to monitor and compare the changes in the molar percentage of fatty acyl groups and the concentrations of primary and secondary oxidation compounds between the unoxidized control,lipoxygenase-catalyzed oxidation and thermal oxidation(in water bath at 95℃)groups.The results showed that phosphatidylcholine and phosphatidylethanolamine were the major components of egg yolk phospholipids.After oxidation of egg yolk phospholipids,the contents of phosphatidylcholine and phosphatidylethanolamine decreased,while the content of hemolytic phospholipids increased.The molar percentage of total unsaturated fatty acids in both oxidized samples decreased,while the molar percentage of saturated fatty acids increased.The degradation rate of linoleic acid was the fastest with the enzyme at pH 6,and more hydroperoxide was formed from the enzymatic oxidation of egg yolk phospholipids.(Z,E)-2,4-dienal was mainly produced after heating.At pH 9,hydroperoxide was produced and rapidly degraded and more n-alkaldehyde was generated after heating.Therefore,lipoxygenase can be used to catalyze the oxidation of egg yolk phospholipids at pH 6 to produce more flavor compounds such as 2,4-diene aldehydes.