黄芩绿变的机理及其控制

The Radix of Scutellaria baicalensis Georgi is a widely used traditional Chinese medicine in clinical practice, and "greening" is a universal phenomenon existing in the collection, processing and storage, which lowers the quality of the medicine. It is generally believed that greening is caused by baicalin, which is hydrolyzed into baicalein and then oxidized to quinone by enzymes. This viewpoint is inconsistent with the results of our previous experiments. In our studies we found that the presence of new components with nitrogenous base are closely related with its greening, therefore, we put forward a hypothesis as follows: pigment precursor is produced through multi-step reactions dominated by enzyme firstly, then the pigment precursor was further reacted with flavonoids, and the green compounds are generated.. Based on this hypothesis, a variety of analytical and preparative chromatography methods are adopted to identify and separate the new ingredients produced in the greening, then the formation of pigment precursor and green pigment was deduced by enzymatic reaction in vitro. Moreover, the content of the key intermediate products in three carboxylic acid cycle was determined. According to the content relationships of the pigment precursor between intermediate products and degree of greening, the greening mechanism will be clarified. This study could provide a theoretical basis for the prevention of its quality deterioration, and the improvement of processing methods for the guarantee of its quality and safety.

黄芩是我国常用大宗药材，临床应用广泛。绿变是黄芩采收加工、储藏等过程中极易出现的品质劣变现象。一般认为黄芩绿变是由于黄芩苷在酶的作用下水解为黄芩素，进而氧化成醌类物质引起，而这与我们前期研究结果存在差异。本项目组前期研究发现，黄芩绿变与其发生过程中出现的含氮新成分有密切关系，故此提出“黄芩绿变是酶主导下经过多步酶促反应产生含氮色素前体，进而与黄芩中黄酮等羰基化合物反应生成绿色物质”的假设。. 基于该假设本研究拟采用多种现代色谱分析、分离技术对黄芩绿变过程中产生的新成分进行识别、分离纯化，并通过体外酶促反应确认色素前体并阐明绿色素的形成过程。同时，通过分析三羧酸循环关键中间产物的含量变化与色素前体含量及绿变程度的关系，阐明绿色素形成的原因及其影响因素。本研究可为黄芩绿变防控提供理论依据，为黄芩用药的安全性、质量的稳定性提供保障。

黄芩是我国常用大宗药材，临床应用广泛。变绿是黄芩采收加工、储藏等过程中极易出现的品质劣变现象。一般认为黄芩变绿是由于黄芩苷在酶的作用下水解为黄芩素，进而氧化成醌类物质引起，然而目前并未有黄芩变绿机理的系统研究报道。基于此，本项目采用液相色谱‒质谱联用方法对黄芩变绿前后的成分进行识别，采用化学、体外酶促方法对黄芩中单体成分的变绿现象进行模拟，探讨黄芩变绿的机制。黄芩变绿前后HPLC-Q-TOF MS成分差异结果显示，鲜黄芩中含有降解苷类成分的酶，这种酶解反应是黄芩变绿的关键环节。对黄芩中获得的单体成分进行络合及氧化反应模拟，并通过紫外、红外光谱对络合产物进行分析，发现黄芩素可与钙离子和镁离子在弱碱性条件下发生络合反应，生成蓝色或黄绿色的稳定产物，这种产物与黄芩药材变绿生成物质的物理特性相似，因此推测黄芩变绿与黄芩中黄酮类成分与金属离子络合有关。鲜黄芩中富集得到的酶可催化黄芩苷镁和黄芩苷生成黄芩素，但是与黄芩苷反应时未见绿色物质生成，与黄芩苷盐反应却生成了绿色物质，说明金属离子是黄芩变绿的关键因素。综上，黄芩变绿是由于药材中含有大量的降解黄芩苷等多种葡萄糖醛酸苷的酶，同时由于黄芩中的黄芩苷在植物中多以黄芩苷镁盐的形式存在，在酶降解时，生成黄芩素的同时，也产生了大量的镁离子，游离的镁离子与黄芩素的在一定的情况下发生络合反应，进而产生绿色物质。以上研究对提升黄芩的质量，指导产地加工等具有重要的现实意义。