基于热重法的植物油氧化动力学研究
Study on the oxidation kinetics of vegetable oils by thermogravimetry
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摘要: 采用热重(TG)及微商热重(DTG)法研究了6种市售植物油的氧化特性,探究了不同升温速率对TG及DTG曲线的影响,通过DTG曲线确定了不同植物油在不同升温速率下的起始氧化温度,并利用Ozawa-Flynn-Wall方程及Arrhenius方程对油脂的氧化进行了动力学参数的推导,同时分析了油脂热降解特性与其主要脂肪酸组成间的相关性。研究表明:随着升温速率的升高,氧化分解的温度随之升高,油脂的起始氧化温度、活化能等参数均可用于表征油脂的氧化稳定性,且植物油的热降解特性与其脂肪酸组成间有着不同程度的相关性;其中油脂的起始氧化温度与其饱和脂肪酸、单不饱和脂肪酸及代表脂肪酸含量成正比,与多不饱和脂肪酸含量成反比;油样的活化能及前指数因子同样也与饱和脂肪酸含量成正比且前者相关性显著,而速率常数κ与样品组分相关性与Ton-组分相关性趋势相反。热重分析法采样量少,操作简单快速,精密度高,可为油脂加工及储藏条件的控制、新型抗氧化剂研发等提供实验依据。Abstract: In this paper,thermogravimetry(TG) and derivative thermogravimetry(DTG) methods were applied to study the oxidative properties of 6 commercial vegetable oils. The effect of heating rate on the TG and DTG curves was investigated and the onset oxidation temperatures(Ton) of oils under different heating rates were confirmed using DTG curves. Through applying Ozawa- Flynn- Wall and Arrhenius equation, the kinetic parameters of oil oxidation were calculated. A correlation analysis between oil degradation properties and their major fatty acids compositions was also studied. The results showed that the oxidation decomposition temperature increased as the heating rate went up. The onset oxidation temperature,activation energy etc.could be used to feature the oxidation stability of vegetable oils. Correlations at different levels were found between thermal- degradation properties of oils and their fatty acid compositions : the onset oxidation temperatures of oil were found to be positive correlated with their amount of saturated fatty acid(SFA),monounsaturated fatty acid(MUFA) as well as typical FAs,while negative correlation was found between Ton and polyunsaturated fatty acid(PUFA). As for Ea and A,both were positive associated with SFA content and the former was statistically significant. With regard to rate content,contrary trend was found compared with Toncomposition relationship. TG analysis was known as an easy-operating,time-saving method with less sample mass and high precision. It could be used to offer experimental bases for the condition control of oil processing and storage as well as the exploration of new antioxidants.