## 1 Introduction
reported the reaction process of fresh leaves with 300 mg/L of ZnCl\({}_{2}\) at pH 5, 110 \({}^{\circ}\)C, and a reaction time of 15 min [25]. The study leads to the formation of Zn-chlorophyll derivatives in pandan leaves, such as Zn-pheophytin and Zn-pyropheophytin. Similar to native chlorophylls, these derivatives are green in colour but more stable to acid and heat while functioning as antioxidants [26]. Meanwhile, [PERSON] et al. proved that the heating process of avocado pures added with Cu or Zn produced a higher puree colour than non-treated samples at approximately 87 to 89 \({}^{\circ}\)C [19]. The results agreed with those reported by [PERSON] et al. and [PERSON] et al., in which the colour stability of Zn- and Cu-based chlorophylls in vegetables was improved by temperature values higher than 85 \({}^{\circ}\)C [22; 27]. [PERSON] et al. [28] reported that the optimum stabilisation conditions of suji leaves (_Pleomele Angustifolia_ Roxb.) were obtained using 700 mg/L of ZnCl\({}_{2}\). The study was performed at pH 7, at a temperature of 85 \({}^{\circ}\)C, and with a total chlorophyll content of 47.29 mg/100 g fresh weight. In Cu and Zn complexes, they are known not to be absorbed by the body and are removed as excretion products. Hence, these complexes are safe and permitted to be utilised in most countries as food additives. Nevertheless, the Food and Drug Administration (FDA) regulation limits that only 75 mg/L of Zn can remain in the final product, while the concentration of free ionisable Cu must be kept below 200 mg/L [17; 29; 30]. Furthermore, these metal ions, such as Cu, Zn, Mg, Ca, and Fe, play an important role in biological and biomedical processes [31]. A study by [PERSON] et al. and [PERSON] et al. discovered that in vitro anti-mutagenic activity of natural chlorophylls and commercial-grade derivatives, such as sodium copper chlorophyllin (SCC) was associated with a decreased risk of colon cancer and numerous dietary and environmental mutagens [12; 32]. [PERSON] et al. [33] further proved that SCC has been utilised in several countries as a food colourant and nutritional supplement without adverse effects for over 50 years. Moreover, SCC is promoted for its anti-bacterial and anti-viral properties [34; 35]. Another study by [PERSON] et al. [16] discovered substantially higher antioxidant capacities of metallo-chlorophyll derivatives (such as Cu-pheophytin a, Cu-chlorophyll, Zn-pheophytin, and Zn-pyropheophytin) than natural chlorophylls and Mg-free derivatives. Other researchers also reported similar results on the antioxidant activities of metal ions containing chlorophylls, such as Cu-pheophytin, Cu-chlorophyll, Zn-pheophytin, Zn-pyropheophytin, and Mg-chlorophyll [36; 37; 38]. Although the method of stabilising chlorophylls has been successfully employed with several vegetables, there is still a lack of information on the use of Zn and Cu to stabilise the chlorophylls in green amaranth purees. Thus, this research aims to investigate the stabilisation process of chlorophylls in amaranth purees, which includes the effect of various metal concentrations, pH, and temperatures. Furthermore, the obtained results were further utilised to evaluate the colour intensities, chlorophylls and their derivative contents, and antioxidant activities of the metal-stabilised amaranth purees. The research suggests that stabilization of green amaranth with different metal ions and conditions has the potential to preserve the green colour and antioxidant activity of amaranth for further use in food processing.