Views:14 Author:Site Editor Publish Time: 2021-04-29 Origin:Site
Spectral characteristics of roselle（Hibiscus) red pigment
It can be seen from Figure 1 that the maximum absorption wavelength of the roselle red pigment measurement solution is 520nm.
Some Factors that affect the stability of Roselle red pigment:
pH value (See Table 1); The Roselle Red Pigment is most stable when PH value between 2.98 and 3.46; When PH value>3.46, the color gradually decreased till PH value up to 6.33. Once PH>6.33, The pigment turned yellow and stronger yellow with the increase of pH value.
Heat resistance (see Table 2): The residual rate of the pigment after 1 hour of water bath with absorbance of 30℃ and 60℃ is relatively large, and the residual rate of the pigment is very small after 1 hour of water bath at 80℃ and 90℃.
Lightfastness (see Table 3): it turns yellow after 48 hours of light under the condition PH 4.9; The absorbance remains 57.6% when PH2.6 and after 72 hours of light, indicating that the roselle red pigment is not resistant to light, so it should be stored away from light.
Metal ions: After adding NaCI, CaCl2, MgCl2, the color of roselle red pigment test solution increased compared with the control group; The solution with ZnCl2, MnCl2 decreased slightly, but not obvious; The pigment solution added with FeCl3 and CuCl2 turns yellow, and the absorbance is significantly reduced. The pigment solutions added with SnCl2 and SnCl4 all produced purple-red flocculent precipitate, and the precipitated solution was colorless and transparent. The reason is: NaCI, CaCl2, MgCl2 provide CI-, which combines with roselle red pigment to form a stable structure; Fe3, CU2 have oxidizing properties, so that AH+ is oxidized into a blue quinoid base.