According to the results shown in Fig. 5, addition of metal ions Mg2+, Zn2+, Cu2+, and K+ in the grape puree with pH 3 reduced the relative chlorophyll pigment retention at 20 °C for 30 min treatment in the order of K+, Cu2+ and Mg2+ similar to Zn2+. However, addition of these metal ions in the grape puree with pH 4 enhanced the chlorophyll pigment retention at 20 °C for 30 min treatment in order of Cu2+, Mg2+, K+ and Zn2+. Therefore, pH values should be taken into consideration when metal ion addition is used to enhance chlorophyll pigment retention in food processing