## 3 Results  
Figure 1 shows the effect of the different (A) solvents, (B) pH values (3-12), (C) temperatures (20-40 \({}^{\circ}\)C), and (D) media (rice, malt, wheat, and fermented wheat bran) used to extract antioxidant compounds by _Aspergillus flavus_ after 15 days of growth at 30 \({}^{\circ}\)C. Based on this, the fermentation of _A. flavus_ on rice medium, with 15 days of incubation at 30 \({}^{\circ}\)C at pH 7 was chosen as the optimal procedure for the production of antioxidant compounds. The antioxidant activity of the optimized ethyl acetate extract of fermented rice (koji) inoculated with _A. flavus_ was compared to the synthetic antioxidant BHT and the natural antioxidant \(\alpha\)-tocopherol at concentrations of 200 \(\upmu\)g/mL, as shown in Table 1. The antioxidant efficacy was comparable to that of commercial extracts. \begin{table}
\begin{tabular}{c c} \hline \hline
**Sample (\(\upmu\)g/mL)** & **Antioxidant Efficacy [\%] \({}^{\ast}\)** \\ \hline BHT & 85.2 \({}^{\text{a}}\)\(\pm\) 1.12 \\ \(\alpha\)-Tocopherol & 82.0 \({}^{\text{b}}\)\(\pm\) 1.04 \\ _Aspergillus flavus_ extract & 73.1 \({}^{\text{c}}\)\(\pm\) 1.56 \\ \hline \hline \end{tabular} \({}^{\ast}\) The different letters indicate significant differences at the probability level \(p<0.05\).  
\end{table} 
Table 1: Antioxidant activity of the ethyl acetate extract of fermented rice (koji) using _A. flavus_. Figure 1: (**A**) Effect of using different solvents on the effectiveness of antioxidant compounds of fermented rice (koji) inoculated with _A. flavus_ following 15-days of incubation at 30 \({}^{\circ}\)C. (**B**) Effect of different pH values on the effectiveness of antioxidant compounds of fermented rice (koji) inoculated with _A. flavus_ following 15-days of incubation at 30 \({}^{\circ}\)C. (**C**) Effect of different temperatures on the effectiveness of antioxidant compounds. Compounds of fermented rice (koji) inoculated with _A. flavus_ following 15-days of incubation at pH 7. (**D**) Effect of different fermentation media on the effectiveness of antioxidant compounds of fermented rice (koji) inoculated with _A. flavus_ following 15-days of incubation at 30 \({}^{\circ}\)C. \({}^{\ast}\) The different letters indicate significant differences at the probability level \(p<0.05\). The free radical scavenging activity, Fe\({}^{2+}\) binding ability, and Fe\({}^{3+}\) reducing ability of fermented rice (koji) extract inoculated with _A. flavus_ are reported in Figure 2. The free radical scavenging activity was marginally less than that of commercial antioxidant BHT, which also follows from their antioxidant efficacy reported in Table 1. The Fe\({}^{2+}\) binding power of _A. flavus_ extracts were also slightly less than that of EDTA-2 Na. Similarly, as compared to BHT, the Fe\({}^{3+}\) reducing power was a little lower for the _A. flavus_ extract. The effect of pH on the ability of these fermented rice (koji) extracts to inhibit the oxidation of linoleic acid at 40 \({}^{\circ}\)C incubation for 80 h is reported in Table 2, wherein biosynthesized antioxidants were found to be most stable under neutral pH, with increasing activity up to 80 h of incubation, whereas the stability was lower under acidic and basic pH. The effect of thermal treatment on the effectiveness of antioxidant compounds of fermented rice (koji) extracts on heating at 185 \({}^{\circ}\)C at different time intervals are reported in Table 3. It was seen that the heating at 185 \({}^{\circ}\)C did not reduce the antioxidant efficacy significantly for up to 10 min, and started decreasing afterwards. Even after 120 min of heating, up to 92.7% of antioxidants were retained, demonstrating good stability of the biosynthesized antioxidants. \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Duration of** & & & & & & & \\
**Incubation** & & & & & & & \\
**(Hours)** & & & & & & & & \\ \hline \multicolumn{6}{c}{**pH = 9**} & \multicolumn{2}{c}{**pH = 7**} & \multicolumn{2}{c}{**pH = 5**} & \multicolumn{2}{c}{**pH = 3**} \\ \hline  & _A. flavus_ & **Control** & _A.