# Antioxidant Properties of Soybean Oil Supplemented with Ginger and Turmeric Powders
## 3 Results and Discussion
### Oxidative Stability of Ginger- and Turmeric-Supplemented Soybean Oils
However, the percentage reductions of IP values in TR (68% at Cycle 2 and 72% at Cycle 3) and TP (63% at Cycle 2 and 81% at Cycle 3) were higher than those in TC (56% at Cycle 2 and 62% at Cycle 3) as a consequence of their greater percentage reductions of curcumin content (Table 1) and antioxidant activity (Table 2). Regarding ginger-supplemented soybean oils, GP, which showed the best oxidative stability at each oil enrichment cycle, had lower IP percentage reductions (55% at Cycle 2 and 65% at Cycle 3) than those of GR (58% at Cycle 2 and 68% at Cycle 3) and GC (53% at Cycle 2 and 70% at Cycle 3) as a consequence of its lower percentage reduction of 6-gingerol content (Table 1) and antioxidant activity (Table 2). As shown in Figure 2, the positive correlation between IP and HPLC values in soybean oils with ginger (\(r\) = 0.87, \(r^{2}\) = 0.79) and turmeric (\(r\) = 0.93, \(r^{2}\) =0.82) powders was statistically relevant (\(p<0.001\)). The IP values linearly increased at increasing contents of bioactive compounds. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{6}{c}{**Soybean Oils 2**} \\ \cline{2-9}  & **C** & **BHT** & **GC** & **GP** & **GR** & **TC** & **TP** & **TR** \\ \hline \multicolumn{9}{c}{**Cycle 1**} \\ \hline IP (h) & 4.71 \(\pm\) 0.10 \({}^{\rm f}\) & 5.04 \(\pm\) 0.36 \({}^{\rm f}\) & 7.39 \(\pm\) 0.19 \({}^{\rm d}\) & 8.25 \(\pm\) 0.16 \({}^{\rm o}\) & 7.60 \(\pm\) 0.18 \({}^{\rm bc}\) & 6.15 \(\pm\) 0.13 \({}^{\rm e}\) & 8.80 \(\pm\) 0.18 \({}^{\rm b}\) & 10.11 \(\pm\) 0.58 \({}^{\rm a}\) \\ \hline \multicolumn{9}{c}{**Cycle 2**} \\ \hline IP (h) & 4.71 \(\pm\) 0.10 \({}^{\rm a}\) & 5.04 \(\pm\) 0.36 \({}^{\rm a}\) & 3.50 \(\pm\) 0.24 \({}^{\rm b}\) & 3.70 \(\pm\) 0.08 \({}^{\rm b}\) & 3.17 \(\pm\) 0.11 \({}^{\rm bc}\) & 2.73 \(\pm\) 0.19 \({}^{\rm c}\) & 3.23 \(\pm\) 0.04 \({}^{\rm bc}\) & 3.21 \(\pm\) 0.10 \({}^{\rm bc}\) \\ \hline \multicolumn{9}{c}{**Cycle 3**} \\ \hline IP (h) & 4.71 \(\pm\) 0.10 \({}^{\rm a}\) & 5.04 \(\pm\) 0.36 \({}^{\rm a}\) & 2.24 \(\pm\) 0.02 \({}^{\rm d}\) & 2.87 \(\pm\) 0.07 \({}^{\rm b}\) & 2.40 \(\pm\) 0.12 \({}^{\rm o}\) & 2.36 \(\pm\) 0.01 \({}^{\rm o}\) & 1.72 \(\pm\) 0.10 \({}^{\rm o}\) & 2.79 \(\pm\) 0.03 \({}^{\rm bc}\) \\ \hline \end{tabular} \({}^{1}\) Cycle 1: oil enrichment with original powders; Cycle 2: oil enrichment with exhausted and one time recycled powders; Cycle 3: oil enrichment with exhausted and two times recycled powders; 5: CO control without antioxidant addition; BHT: 0.02%-wide budgetly hydrovolteness sympathetic reference antioxidant; GC: commercial ginger; GP: free-dried ginger peel; GK: free-dried ginger shimoene; TC: commercial tur turne; TP: free-grade dried turne; peel; TR: free-dried turne; Arizona. \({}^{\rm o}\) Data are presented as mean \(\pm\) SD (\(\mu\) = 3). Values with different letters within rows are statistically different (\(p<0.05\)) as determined by Bonferroni test.  
\end{table} 
Table 3: The oxidative stability index of soybean oils with/without antioxidant powders at different oil enrichment cycles \({}^{1}\).