Quality indices
The high temperature used in roasting can promote lipid oxidation, which in turn influences the quality of a peanut oil (Al Juhaimiet al., 2018). The results show that the BIs of the peanut oils generated by different roasting temperatures in this study ranged from 37.94~195.71(Table 1). Simultaneously, the color of peanut oil changes from a dark yellow to red brown as roasting temperature increased. Furthermore, the AVs of the peanut oils generated by different roasting temperatures ranged from 1.12~1.94mg KOH/g, while the POVs of the peanut oils generated by different roasting temperatures ranged from 5.48~8.67 meq peroxide/kg. These values meet the Chinese National Standard criteria for peanut oil. AV and POV determinations are often used as general indications of the condition and edibility of oils. When an oil has a POV>10 meq peroxide/kg, it is less stable and to have a short shelf life (Madhujith and Sivakanthan, 2018). Relatedly, oxidation products can cause undesirable health problems. The result show that the p–AVs of the peanut oils were generated by different roasting temperatures in this study ranged from 5.47~10.42 meq/kg. We further found that the TOTOX values of the peanut oils generated by roasting at 120℃, 140℃, and 160℃ were 16.43, 26.70, and 27.76, respectively. The quality standards of the European Pharmacopoeia require specific levels of TOTOX ≦30(Xu et al., 2015).
Various fatty acids influence the nature of an oil’s physicochemical and nutritional performance. Regarding the fatty acid compositions of the peanut oils generated after roasting in this study, we found out 8 kinds fatty acids. The obtained data further showed that no significant differences in fatty acid composition for the oils generated by different roasting temperatures (Table 2, p<0.05). Oleic acid (36.67~38.44%) is an important nutritional component of peanut oil. Compared with PUFA, oleic acid is more resistant to thermal oxidation, both at ambient storage temperatures and the high temperatures that prevail during cooking and frying of food (Penget al., 2017). Relatedly, vegetable oils with higher U/S ratios are more precious in terms of nutritional quality, as they may contribute to a greater extent to lowering the LDL cholesterol and total cholesterol of people, while not affecting their levels of beneficial HDL cholesterol (Hashempour–Baltork et al., 2016; Cicero et al., 2018). We found that the UFA/SFA values of the peanut oils generated by roasting in this study ranged from 3.58~3.68. Other studies have indicated that the U/S values of camellia seed oils ranged from 3.23~3.31(Yang et al., 2018).