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.