Red cabbage anthocyanins: The influence of D-glucose acylation by hydroxycinnamic acids on their structural transformations in acidic to mildly alkaline conditions and on the resulting color
Red cabbage anthocyanins: The influence of D-glucose acylation by hydroxycinnamic acids on their structural transformations in acidic to mildly alkaline conditions and on the resulting color
复制标题
DOI：
10.1016/j.dyepig.2018.05.057
复制
发表时间：
2018-11-01
影响因子：
4.5
通讯作者：
Dangles, Olivier
中科院分区：
文献类型：
--
作者：
Moloney, Micheal;Robbins, Rebecca J.;Dangles, Olivier
羟基肉桂酸酰化的花青素是一种迷人的植物色素，通过多种结构转变和分子间相互作用，可呈现红、紫、蓝等多种颜色。酰化花青素也是人工食品着色剂的一种有前途的替代品。本工作采用核磁共振、紫外-可见光谱和圆二色谱等方法对红甘蓝单酰化和双酰化花色苷进行了研究。我们的研究结果表明，HCA残基促进酚核之间的π-堆积相互作用，从而有效地保护矢车菊色素发色团对水的加成导致无色的形式。例如，加水的速率常数为ca。0.3 s（-1），对于三种单酰化颜料在0.1-0.2 s（-1）的范围内，对于三种二酰化颜料在0.01 s（-1）的量级。相比之下，水消除的速率常数和阳离子，中性和阴离子的有色形式之间的质子转移的热力学常数只有微弱的影响，酰化。因此，通过π-堆积相互作用，双酰化花青素苷在弱酸性条件下平衡时保持较高百分比的阳离子和中性着色形式。在中性-弱碱性条件下，双酰化花青素苷采用持久的阴离子形式（非常缓慢的加水），表现出强烈的蓝色。NMR和CD数据表明，矢车菊素- HCA（分子内共色素化）和矢车菊素-矢车菊素（自缔合）相互作用的组合在颜色稳定机制中起作用，这也转化为对温和碱性条件下的长期颜色损失的改善的抗性，表明发色团的不可逆降解。
Anthocyanins acylated by hydroxycinnamic acids (HCAs) are fascinating plant pigments that express a variety of red, purple and blue colors by combining multiple structural transformations and molecular interactions. Acylated anthocyanins are also a promising alternative to artificial food colorants. In this work, the mono- and diacylated anthocyanins of red cabbage have been extensively studied by NMR, UV-visible spectroscopy and circular dichroism. Our results show that HCA residues promote pi-stacking interactions between the phenolic nuclei, thereby efficiently protecting the cyanidin chromophore against water addition leading to colorless forms. For instance, the rate constant of water addition is ca. 0.3 s(-1) for the nonacylated pigment, in the range 0.1-0.2 s(-1) for the three monoacylated pigments and of the order of 0.01 s(-1) for the three diacylated pigments. By contrast, the rate constant of water elimination and the thermodynamic constants of proton transfer between the cationic, neutral and anionic colored forms are only weakly affected by acylation. Thus, through pi-stacking interactions, the diacylated anthocyanins maintain a higher percentage of cationic and neutral colored forms at equilibrium in mildly acidic conditions. In neutral - mildly alkaline conditions, the diacylated anthocyanins adopt persistent anionic forms (very slow water addition), expressing intense blue colors. NMR and CD data suggest that a combination of cyanidin - HCA (intramolecular copigmentation) and cyanidin - cyanidin (self association) interactions operates in the color-stabilizing mechanism, which is also translated in an improved resistance against the long-term color loss in mildly alkaline conditions, signalling the irreversible degradation of the chromophore.