## 2 Results and Discussion
### Effect of Microwave Pretreatment on the Free Phytosterols and Tocpherols Content of Oil  
Phytosterols are not only generally recognized as providing significant lowering of serum low-density lipoprotein (LDL) cholesterol in humans, but has also shown protection against various chronic ailments like cardiovascular disease, hepatoprotective, diabetes, and cancer [6; 7]. The main phytosterol sources are vegetable oils. The free-form sterols have higher efficacies (in human subjects) than sterol esters [6]. The effect of MW pretreatment on free phytosterols content in extracted oil is shown in Table 2. The free phytosterols content of oil from untreated peanut was \(273.55\pm 2.51\) mg/100 g. The content of free phytosterols significantly (\(p\) < 0.05) increased with increasing MW treatment time. With 5 min of MW treatment, the free phytosterols in the extracted oil reached the maximum content (363.35 \(\pm\) 4.22 mg/100 g), which was 32.83% higher than the control. Previous research reported that 4-8 min of MW treatment of rapeseed could increase phytosterols by 57.73-140.96 mg/100 g in the oil extracted by cold pressing, which was 10.18-18.36% higher than the control [10; 19; 20]. Comparing with the MW effect on rapeseed, MW pretreatment on peanuts has more obvious improvement in the percentage of free phytosterols content enhancement in extracted oil to the initial content in the control sample. Tocopherols are natural antioxidants that inhibit lipid oxidation in oil. There are significant differences within the tocpherols profile among different peanut cultivars. The content of four types of tocopherols (\(\alpha\)-, \(\gamma\)-, \(\delta\)- and \(\beta\)-) in peanut oils are 18-57%, 36-78%, ND-6% and ND-2%, respectively [5]. The free form of tocopherols has higher bioaccessibility than the esterified form, because it is easier to incorporate into mixed micelles [30]. The free tocopherols profile of extracted oil is shown in Table 2. \(\beta\)-tocopherol was not detected in the oil samples in this study. The extracted oil from untreated peanuts has 18.42 \(\pm\) 0.29 mg/100 g free tocopherols including 13.87 \(\pm\) 0.27 mg/100 g  
\begin{table}
\begin{tabular}{c c c c c} \hline
**MW Time** & **Color** & **Color** & **Acid Value** & **Pexoxide Value** \\
**(min)** & **(Red Units)** & **(Yellow Units)** & **(mg KOH/g Oil)** & **(meq O\({}_{2}\)/kg Oil)** \\ \hline
0 & 0.00 \(\pm\) 0.00 f & 1.20 \(\pm\) 0.10 c & 0.31 \(\pm\) 0.02 d & 0.54 \(\pm\) 0.08 e \\
1 & 0.10 \(\pm\) 0.00 e & 1.40 \(\pm\) 0.00 c & 0.41 \(\pm\) 0.01 c & 0.64 \(\pm\) 0.00 e \\
2 & 0.20 \(\pm\) 0.00 d & 2.37 \(\pm  
\(\alpha\)-tocopherol, 3.97 \(\gamma\)-tocopherol and 0.58 \(\pm\) 0.02 mg/100 g \(\delta\)-tocopherol. MW pretreatment of peanut significantly (\(p\) < 0.05) increased the concentration of all types of free tocopherols in oils. With 5 min of MW treatment, the \(\alpha\)-, \(\gamma\)- and \(\delta\)-tocopherol in extracted oil all reached the maximum content (21.36 \(\pm\) 0.24 mg/100 g, 5.66 \(\pm\) 0.04 mg/100 g and 0.86 \(\pm\) 0.02 mg/100 g, respectively). The total free tocopherols content in extracted oil from 5 min of MW-treated peanut was 27.88 \(\pm\) 0.27 mg/100 g, which was 51.36% higher than the control. The damages in the lipoprotein membrane surrounding individual lipid bodies and the promoting passage of oil from cell membrane may contribute to the release of tocopherols and improving their content in the extracted oil. Contrary to our results, decreasing tocopherols content of oil from 6-30 min MW roasted peanut was reported [24]. The tocopherols content in extracted oil from MW-treated rapeseed increased to maximum at 6 min radiation for dehulled seeds and 4 min radiation for whole seeds, and then decreased with longer treatment time. Total tocopherols in oil from MW treated rapeseed was increased to 1.08-2.61 mg/100 g, which was 1.5-4% higher than control [19]. Similar results were reported [20].