胆固醇在三硬脂酸甘油酯和三油酸甘油酯中的高温氧化特性

Thermo-oxidation of Cholesterol in Glyceryl Tristearate and Glyceryl Trioleate

为了阐明组成三酰甘油的脂肪酸是否饱和对胆固醇氧化的影响,使用气相色谱-质谱联用技术研究了胆固醇在三硬脂酸甘油酯(GTS)和三油酸甘油酯(GTO)中的氧化情况,并同步跟踪过氧化值的变化。结果表明:胆固醇在GTS和GTO中的主要氧化产物为7α-羟基胆固醇、7β-羟基胆固醇、5,6β-环氧基胆固醇、5,6α-环氧基胆固醇、7-酮基胆固醇。在160℃加热条件下,胆固醇氧化产物随时间先增加后减少,未氧化胆固醇逐渐减少,在GTO中过氧化值在加热1 h出现最大值(500.46 meq/kg),在GTS中过氧化值在加热3 h出现最大值(401.30 meq/kg),随后逐渐降低。在110℃加热条件下,胆固醇在GTS中不会氧化,过氧化值亦较低,加热96小时出现最大值(278.43 meq/kg),胆固醇在GTO中几乎完全氧化,过氧化值迅速增加,最大值出现在加热12 h(1486.88meq/kg),随后逐渐减少。总的来说,160℃和110℃加热条件下,胆固醇在GTS中比在GTO中稳定,过氧化值的产生亦会延迟且生成量较小,因此,饱和脂肪酸三酰甘油更有助于保持胆固醇在高温下的稳定性。

In order to elucidate the effects of saturation of fatty acids in triglycerides on cholesterol oxidation, thermo-oxidation of cholesterol in glyceryl tristearate（GTS） and glyceryl trioleate （GTO） was investigated by GC-MS, and their peroxide values were also measured. The results indicated that the main cholesterol oxidation products in GTS and GTO were 7α-hydroxycholesterol, 7β-hydroxycholesterol, 5,6β-epoxycholesterol, 5,6α-epoxycholesterol, and 7-ketocholesterol. At 160 ℃, the cholesterol oxidation products increased and then decreased over heating time, while unoxidized cholesterol reduced gradually in the process. The highest peroxide value （500.46 meq/kg） in GTO was achieved after 1 h heating. The peroxide value in GTS increased to the highest value of 401.30 meq/kg after 3 h heating, but then decreased with prolonging the treatment time. At 110 ℃, no cholesterol oxidation occurred in GTS, and the peroxide value kept lower, with its peak value （278.43 meq/kg） appearing after 96 h heating. However, cholesterol was almost completely oxidized in GTO, and the peroxide value increased rapidly, reaching its highest （1486.88 meq/kg） after 12 h heating, and then gradually decreased. Generally, cholesterol was more stable in GTS than GTO at 160 ℃ and 110 ℃, and the appearance of peroxide delayed with lower amounts. It was suggested that the saturated fatty acids in triglycerides were more beneficial to stabilize cholesterol under high temperature.