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Oxidation degree of soybean oil at induction time point under Rancimat test condition: Theoretical derivation and experimental observation

Li, Xu, Li, Yongru, Yang, Fan, Liu, Ruijie, Zhao, Chenwei, Jin, Qingzhe, Wang, Xingguo
Food research international 2019 v.120 pp. 756-762
acid value, butyric acid, cooking fats and oils, equations, fatty acid composition, ion exchange chromatography, models, nuclear magnetic resonance spectroscopy, oxidation, peroxide value, shelf life, soybean oil, temperature
Indices including conductivity, short-chain carboxylic acids, total polar material, acid value, peroxide value and fatty acid composition in water or oil were monitored during Rancimat test of soybean oil from 90 °C to 120 °C. Formic, acetic, propionic and butyric acids in water were detected by ion chromatography. The results showed that all indices had two-stage oxidation rates of initiation (ki) and propagation (kp) at each temperature. Induction period (IP) computed from conductivity and other indices were well correlated (R2 = 0.9980–0.9999). According to the Arrhenius model and empirical equation, ki increased exponentially with temperature (T) while IP decreased exponentially with T. Oxidation degree of oil at induction time point IP*ki was found to be independent of heating time and temperature. The transition between two models was theoretically derived and proved by H NMR. Evaluation of IP*ki may provide a new route to correlate Rancimat data with shelf life of edible oil.