Enzymatic Synthesis of Myristoyl Cyanidin-3-O-Glucoside in a Mixed Solvent System
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Abstract:
In order to improve the stability and lipophilicity of cyanidin-3-O-glucoside (C3G), immobilized lipase Lipozyme 435 was used in this study to catalyze the acylation of C3G by methyl myristate. The acylation in a single organic solvent and a mixed organic solvent was investigated. Then, the acylated derivative of C3G was separated and purified by semi-preparative liquid chromatography, and its structure was characterized by HPLC-MS/MS and NMR techniques. The optimal synthesis conditions of myristoyl C3G were obtained in 20% pyridine-tert-amyl alcohol by single factor experiments and orthogonal experiments. The results showed that the conversion rate in a mixed solvent system (tert-amyl alcohol plus 20% V/V of pyridine petroleum ether, n-hexane or isooctane) was significantly improved (p<0.05) compared to that in a single organic solvent. The 20% pyridine-tert-amyl alcohol combination was the best reaction medium and allowed the increase of the conversion rate from 10.13% to 15.62%. The acylation most likely occurred on the 6″-OH of the glucose residue of C3G to yield cyanidin-3-(6″-myristoyl)-glucoside. The highest conversion rate for myristoyl C3G was achieved (33.25%) under the optimal synthesis conditions: 60 ℃; reaction time, 22 h; molar ratio of C3G to methyl myristate, 1:250; enzyme concentration 20 mg/mL. This study provides a useful reference for further research on the stability and biological activity of anthocyanins, and to expands the application of anthocyanins in lipophilic matrices.
