单宁酸和绿原酸对杨梅花色苷的辅色作用

Study on the copigmentation effects of tannic acid and chlorogenic acid on the anthocyanins of bayberry

通过紫外-分光光度法和CIELab法探究辅色剂单宁酸和绿原酸对杨梅花色苷在水溶液体系中的辅色效果。结果表明,随着单宁酸、绿原酸浓度的增加,杨梅花色苷水溶液的最大吸收波长发生红移,L*值减小,a*值增大。辅色后,杨梅花色苷色泽热稳定性明显提高。通过HPLC进行辅色前后花色苷成分分析,发现加入辅色剂辅色后,无新的花色苷衍生物产生,推测辅色反应为非共价结合。2种辅色作用的吉布斯自由能ΔG均小于0,表明辅色反应是自发进行的;而焓变值ΔH及熵变值ΔS都是负值,表明辅色反应过程是放热的。单宁酸与花色苷辅色反应的平衡常数K值大于绿原酸,说明单宁酸与花色苷的辅色反应更容易进行。

The UV spectrophotometer and CIELab color space assay were used to explore the effects of copigments (tannic acid and chlorogenic acid) on the copigmentation of bayberry anthocyanins in aqueous solutions. The results showed that the maximum absorption wavelength of the anthocyanins aqueous solution exihibited bathochromic shift,the L^* value decreased,and the a^* value increased with increasing concentrations of tannic acid and chlorogenic acid. After copigmentation,the thermal stability of the pigment of bayberry anthocyanins was significantly improved. HPLC was used to analyse the composition of anthocyanins before and after copigmentation,no new anthocyanin derivatives produced after copigmentation,assuming that the copigmentation reaction was non-covalently bound. The Gibbs free energy (ΔG) of the two processes were both less than zero,indicating that the copigmentation reactions were spontaneous. In comparison,Δ H and Δ S were both negative,which indicated that the processes were generally spontaneously exothermic. The equilibrium constant (K) of the reaction of tannic acid group and anthocyanins was greater than chlorogenic acid group,which indicated that tannic acid was more favorable to react with anthocyanins for copigmentation reaction.