## 3 Results and Discussion
### Stabilisation Process of Chlorophylls
#### 3.2.3 Effect of Temperature  
The greenness and chlorophyll derivative content of the Cu-amaranth and Zn-amaranth purees increased with the increasing temperature in Figure 3. Based on the results, the Cu-amaranth puree produced the highest chlorophyll derivative content (0.62 mg/g FW) at 80 \({}^{\circ}\)C and greenness value (\(-\)0.40) at 80 to 100 \({}^{\circ}\)C (Figure 3a). The thermal treatment process was also reported as essential when using metals to retain green pigments. The heat is important in removing carbomethoxyl at the C10 carbon position on the isocyclic ring of chlorophyll, transforming the pyrrole nucleus into a cation [44]. Thus, the transformation improves the diffusion of divalent metal ions (Cu\({}^{2+}\) or Zn\({}^{2+}\)) in dislodging Mg\({}^{2+}\) ions to form metal complexes with chlorophylls [17]. The highest greenness value was depicted with the Zn-amaranth purees at 90 \({}^{\circ}\)C. Meanwhile, the highest chlorophyll derivative content was observed at 90 \({}^{\circ}\)C (0.39 mg/g FW) and 100 \({}^{\circ}\)C (0.37 mg/g FW). In this study, the findings were in line with [PERSON] et al., which reported that avocado purees treated with Cu or Zn at 87 to 89 \({}^{\circ}\)C produced greener colour than untreated samples [19]. Similarly, [PERSON] et al. and [PERSON] et al. reported that treating green vegetables with Cu and Zn and heating them at higher temperatures (>85 \({}^{\circ}\)C) would result in colour improvements [22,27]. [PERSON] et al. also reported that peas blanched in Zn solution (50-500 mg/L) showed increased complex formation during the heat process (121-125 \({}^{\circ}\)C) [22]. The heat treatment process causes chlorophyll derivatives, such as phenophytin, to react with metal ions to form metal-pheophytin complexes with a stable green colour [22,44]. Therefore, heat treatments at 80 \({}^{\circ}\)C (Cu-amaranth puree) and 90 \({}^{\circ}\)C (Zn-amaranth puree) were selected as the optimum stabilisation temperatures. Figure 4 displays the three absorbance spectra of acetone extracts of fresh and metallostabilised amaranth purees. The amaranth purees are mostly absorbed in the blue and red regions of visible light due to the presence of chlorophylls and their derivative forms [53]. All acetone extracts of fresh and metal-stabilised amaranth purees have two major absorption bands in the visible range, which are \"red\" (Q-) and \"blue\" (Soret- or B-) bands [53]. The \"red\" and \"blue\" bands of chlorophyll \(a\) (Q- and B-bands) were located at wavelengths of 662 and 430 nm for acetone solutions, respectively [54]. A difference in the maximum absorption of the amaranth extracts at wavelengths from 350 to 500 nm was displayed in Figure 5 due to the colour differences between fresh amaranth and metal-stabilised pures [18]. The maximum absorption peaks of fresh amaranth puree were located at 433.77 and 668.86 nm wavelengths. Hence, the results were closely related to [PERSON] et al. [52], which concluded that the absorption maxima of chlorophyll \(a\) were at 428.5 and 660.5 nm wavelengths. Furthermore, [PERSON] et al. also reported that the fresh pear peel absorption peaks occurred at wavelengths of 430 and 660.5 nm [18]. Thus, these results indicated that the green colour of fresh amaranth puree was dominated by chlorophyll _a_[18]. For Cu-stabilised pures, the absorption maxima peaks were at wavelengths of 424.93 and 656.85 nm, respectively. The results were consistent with the findings of [PERSON] et al., in which the absorption maxima at the Soret (S-) and Q-bands of Cu chlorophyll \(a\) were at wavelengths of 422 and 652 nm [55], respectively. Based on the amaranth stabilised with Zn, the extracts revealed absorption maxima at 413.28 and 667.48 nm wavelengths. In addition, [PERSON] et al. elucidated that the absorption maxima of [PERSON] seedless grape purees occurred at 664 to 670 nm wavelengths for the complexes with ZnCl\({}_{2}\)[23].