Oxidation stability
Oxidation process accelerate Rancimat test by disclose oil samples to high temperature and high oxygen solubility, and that in turn determine the induction period for the formation of volatile acids (Robertson et al., 2000; Yeh et al., 2014). In this study, we investigated the oxidative stability of the peanut oils generated using the Rancimat test at temperatures of 100~120°C (Fig. 1). For use of the Rancimat test at temperature of 100, 105, 110, 115, and 120℃, the induction times were 13.58, 12.01, 8.56, 4.89, and 3.94 h, respectively, for the oils roasted at 120℃; 20.85, 14.15, 8.75, 5.67, and 3.68 h, respectively, for the oils roasted at 140℃; and 21.55, 15.12, 10.87, 5.88, and 3.71 h, respectively, for the oils roasted at 160℃. Simultaneously, semi–logarithmic relationship for all the oil samples by Equation Ⅰ, including a linear dependency with good correlation of determination, R2 0.959~0.998 for the different roasting temperatures (Fig. 1). The kinetic parameters of the Rancimat test are valuable for the goal of distinguishing between various oils, for characterizing the differences or similarities in oils, and for predicting the oxidative stability of oils under various storage conditions (Kochhar and Henry, 2009). The E a values for all the oil samples were determined using Equation II, the bond scission that take place forming primary oxidation products is shown through the delay of the initial oxidation reaction (Farhoosh and Hoseini–Yazdi, 2014). Table 5 shows that the E a values of the assayed oils were 82.08 kJ/mol for the oil roasted at 120℃, 105.2 kJ/mol for the oil roasted at 140℃, and 108.61 kJ/mol for the oil roasted at 160℃. Other studies have indicated that the E a values for vegetable oils ranged from 86.86~82.42 kJ/mol. The E a value of oil is influenced by level of unsaturated fatty acids and antioxidants present in the oil (Yang et al., 2018).
This study investigated the compound changes and olfactory sensations for peanut oils roasted at different temperatures, which characterized in terms of oxidative stability by PCA (Fig. 2). The key results include the finding: 1) The E a values of the oils indicated that their oxidative stability was highly correlated with their levels of total phenol (R:0.963), DPPH (R:0.963), FRAP (R:0.944), and r–tocopherol (R:0.739). The occurrence of total phenol and γ–tocopherol led to a high Ea value in the products, causing great DPPH and FRAP performance simultaneously. 2) The N–heterocyclic compounds in the oils provided an overall indication of their olfactory sensations. In the process of roasting, the oxide (O–heterocyclic (R:–0.986), aldehyde (R:–0.950), and alcohol (R:–0.890)) compounds generated were transformed into N–heterocyclic compounds as the temperature increased due to the Maillard reaction.