介质pH值对红葱红色素光谱特性及稳定性的影响

Effect of Medium pH Value on the Spectrum Characteristic and Stability of Red Pigments from Eleutherine americana

从鸢尾科红葱中制备天然红色素,用色差计测定红葱红色素在不同pH介质中的色差值(CIE L*a*b*表色系统),并对不同pH介质中红葱红色素的紫外可见吸收光谱以及贮存稳定性进行分析。结果表明:红葱红色素溶液明度偏亮白,色调呈红黄色,紫外可见吸收光谱在可见光波段无特征吸收峰。红葱红色素色泽受介质pH值影响较大,在接近中性的环境中颜色呈纯正柔和的橘红色,在偏酸或偏碱的环境中色泽有明显变化。介质pH对紫外和近紫外区的吸收光谱有较大影响,对可见光区的吸收强度影响较小。介质pH对色素的贮存稳定性影响较大,碱性环境中色素颜色迅速加深,溶液吸光度大幅上升,建议在低酸环境中贮存和使用红葱红色素,有利于色素的稳定。

The chromaticity （CIE L＊ a＊ b＊ value system）of natural red pigments from Eleutherine americana at different pH values is determined with colorimeter, and the UV-visible spectrum and storage stability are analyzed. The results show that the brightness of red pigments from Eleutherine americana is on the white side and the hue is yellow and red. The peak could not be found at the visible wave brand of the UV-visible spectrogram. The color of red pigments from Eleutherine americana is greatly influenced by medium pH value. It shows that sterile and soft jacinth in the medium close to netrual, while its color changes markedly at rather acidity or alkalinity. Medium pH value has noticeable effect on the absorbance of UV and near UV wave brand spectrogram, while it has little effect on the visible segment. Storage stability is greatly affected by medium pH value, the color darkens quickly especially at alkaline medium and the absorbance increases sharply. The appropriate medium pH value range during storage and application is suggested as low acidity, at which the stability is acceptable.