## 3 Results and Discussion
### Antioxidant Activities of Cu- and Zn-Amaranth Purees
#### 3.3.3 Effect of Temperature  
In Figure 8, the Zn-amaranth purees significantly (\(p<0.05\)) displayed the highest DPPH values at 88 mM TE/dry weight at 100 \({}^{\circ}\)C. Conversely, the highest FRAP values range from 57 to 58 mM TE/dry weight at 80 to 100 \({}^{\circ}\)C. A similar trend was also observed for Cu-amaranth purees with the highest DPPH values ranging from 93 to 95 mM TE/dry weight at 80 to 100 \({}^{\circ}\)C. Moreover, the DPPH values were higher than Zn-amaranth purees. Thus, these  
Figure 7: Effect of pH on antioxidant activities of **(a)** 210 mg/L of CuSO\({}_{4}\) and **(b)** 1500 mg/L of ZnCl\({}_{2}\) stabilised amaranth purees after heating at 80 \({}^{\circ}\)C for 15 min. Each value was expressed as mean \(\pm\) standard deviation (\(n=3\)) of triplicate analysis. The bars with different lowercase (a–d) and uppercase (A–E) letters indicate significant differences (\(p<0.05\)) in [PERSON]’s HSD test.  
findings confirmed that the antioxidant activities increased with increasing temperatures, probably due to the formation of firm bonds between Zn or Cu with chlorophyll derivatives. In addition, the metallo-chlorophyll derivatives complexes are more resistant to acid and heat treatments than natural Mg\({}^{2+}\)-chlorophyll complexes [58].  
Identification of Chlorophylls and Their Derivatives in Fresh, Cu-, and Zn-Amaranth Pures Using Reversed-Phase HPLC  
The identification of peaks was confirmed by comparing retention times (t\({}_{\text{ret}}\)) of the peaks in the sample with standard chlorophylls \(a\) and \(b\) (Figure 9a,b). As shown in Figure 9c, the HPLC chromatogram of the chlorophyll fraction from the fresh amaranth extract depicted two major peaks at retention times (t\({}_{\text{ret}}\)) of 16.73 (peak 1) and 27.65 min (peak 2). Hence, these peaks corresponded to chlorophyll \(b\) and chlorophyll \(a\), respectively.  
Figure 8: Effect of temperatures for the reaction time of 15 min on antioxidant activities of (**a**) 210 mg/L of CuSO\({}_{4}\) stabilised amaranth pures at pH 6 and (**b**) 1500 mg/L of ZnCl\({}_{2}\) stabilised amaranth pures at pH 8. Each value was expressed as mean \(\pm\) standard deviation (\(n\) = 3) of triplicate analysis. The bars with different lowercase (a–d) and uppercase (A–C) letters indicate significant differences (\(p\) < 0.05) in [PERSON]’s HSD test.  
Chlorophyll \(b\) appeared to have a shorter retention time in the non-polar C\({}_{18}\) type of column, which is more polar and eluting than chlorophyll \(a\)[59; 60]. The elution order of chlorophylls \(a\) and \(b\) of fresh amaranth extracts coincided with green bean and spinach extracts [51]. Additionally, chlorophylls \(a\) and \(b\) in fresh amaranths were 5.01 mg/g and 1.26 mg/g, respectively. In this study, the chlorophyll content of fresh amaranth puree recorded was higher than green beans (chlorophyll \(a\): 1.11 mg/g, b: 0.74 mg/g) and peas (chlorophyll \(a\): 0.8 mg/g, b: 0.51 mg/g) [61]. Nevertheless, the chlorophyll content of chlorophylls \(a\) and \(b\) in spinach leaves (chlorophyll \(a\): 14.1 mg/g, \(b\): 6.2 mg/g DW) was higher than the amaranth purees reported in this study [62].