酸碱对大豆油脂中反式脂肪酸的影响

Effects of Acid and Alkali on Trans Fatty Acids in Soybean Oil

以常规加热为对照组,通过气相色谱法分析H3PO4处理或NaOH处理对非共轭亚油酸(C18∶2)的热诱导顺/反异构化的分子机制。由加热试验可知,C18∶2-9c,12t和C18∶2-9t,12c为加热大豆油脂中的主要反式异构体。随着加热温度逐渐升高、加热时间的逐渐增强,反式亚油酸含量随之增加。3种油样加热后产生反式脂肪酸的量的排序为:NaOH处理后油样>H3PO4处理后油样>未处理油样。在加热过程中,生成单反式亚油酸的量高于生成双反式亚油酸的量。在温度260℃加热8 h时,经NaOH处理的加热油脂产生的单反式亚油酸(C18∶2-9c,12t)最多,达1.222%。通过Gauss软件对油脂中的双键进行分析,可知常规加热形成C18∶2-9t,12t需要跨越能量分别为235.986,223.846 kJ/mol两个能垒,而当油脂进行H3PO4处理或NaOH处理后产生的反式亚油酸的能垒降低,表明H3PO4处理或NaOH处理均会增加加热油脂反式异构体的几率,其中NaOH处理的影响最大。

The molecular mechanism of the heat-induced cis/trans isomerization of non-conjugated linoleic acid(C18∶2)by alkali treatment and acid treatment was analyzed by gas chromatography with conventional heating as the control group.From the heating test,C18∶2-9c,12t and C18∶2-9t,12c are the main trans isomers in the heating of soybean oil.With the heating temperature gradually increased,the heating time gradually increased,the trans-linoleic acid content also increased,three kinds of oil samples after heating to produce trans fatty acids in the order:alkali treatment oil sample>acid treatment oil sample>Untreated oil sample.In the process of heating,the amount of monovalent linoleic acid produced is higher than the amount of bis-trans linoleic acid produced.When heated at 260℃for 8 h,the amount of mono-functional linoleic acid(C18∶2-9c,12t)produced by heating oil after NaOH treatment,Up to 1.222%.It is found that C18∶2-9t and 12t are required to pass two energy barriers of 235.986 kJ/mol and 223.846 kJ/mol,respectively.The results showed that strong acid treatment or alkali treatment increased the chance of heating the trans isomers of oil,and the effect of strong alkali treatment was the strongest.