Hohenheim University, Institute of Food Science and Biotechnology, Chair Plant Foodstuff Technology, Garbenstrasse 25, D-70599 Stuttgart, Germany.
Food Chem. 2012 Dec 15;135(4):3010-9. doi: 10.1016/j.foodchem.2012.06.101. Epub 2012 Jul 11.
The formation of anthocyanin-metal chelates, exhibiting intense blue colours was monitored over a period up to 10 weeks. Evaluating normalised absorption spectra in the range of 580-700 nm and their proportion of the total area under the curve (AUC), provided information about the blue colour hue, intensity and stability. Colour stability in model solutions containing commercial sugar beet pectin or an isolated pectic polysaccharide fraction (PPF) therefrom, both being naturally enriched in aluminium and ferric ions, was assessed in a pH range of 3.6-7.0. The pectic structures stabilised anthocyanin-metal chelates, and thus blue colours by efficiently preventing complex precipitation. Highest bathochromic shifts and most intense blue colours were observed in PPF model solutions containing delphinidin-3-glucoside (Dpd-3-glc), exhibiting a pyrogallol moiety in the flavylium B-ring, compared to cyanidin- (Cyd-3-glc) and petunidin-3-glucoside (Pet-3-glc), both carrying a catechol substituted B-ring. Hue and intensity of the blue colour at pH 5.0 were only insignificantly influenced by the buffer system except for citrate and phosphate buffers, which both annihilated anthocyanin-metal chelate formation. The blue colours faded following first order kinetics. Best stabilities as deduced from storage experiments performed at 20 ± 2°C in the dark were observed for Dpd-3-glc. In contrast, Cyd-3-glc displayed shortened half-life values, whereas blue Pet-3-glc chelates decomposed rapidly. These results demonstrate that the solubilisation of anthocyanin-metal chelates by pectic structures is a promising option for developing water soluble natural blue food colourants.
花色苷-金属螯合物的形成呈现出强烈的蓝色，在长达 10 周的时间内进行了监测。评估 580-700nm 范围内归一化吸收光谱及其在曲线下总面积（AUC）中的比例，提供了有关蓝色色调、强度和稳定性的信息。在 pH 值为 3.6-7.0 的范围内，评估了含有商业甜菜果胶或其分离的果胶多糖（PPF）的模型溶液中花色苷-金属螯合物的颜色稳定性，这两种物质天然富含铝和铁离子。果胶结构稳定了花色苷-金属螯合物，从而通过有效防止复合物沉淀来稳定蓝色。在含有飞燕草苷-3-葡萄糖苷（Dpd-3-glc）的 PPF 模型溶液中观察到最大的红移和最强烈的蓝色，其在 flavylium B 环中带有邻苯二酚取代基，与带有邻苯二酚取代基的矢车菊苷-（Cyd-3-glc）和锦葵苷-3-葡萄糖苷（Pet-3-glc）相比，在 pH 值为 5.0 时，蓝色的色调和强度仅受到缓冲体系的轻微影响，除了柠檬酸盐和磷酸盐缓冲液，它们都消除了花色苷-金属螯合物的形成。蓝色的颜色遵循一级动力学褪色。在 20±2°C 黑暗条件下进行的储存实验中，根据推断得出的最佳稳定性是 Dpd-3-glc。相比之下，Cyd-3-glc 的半衰期值较短，而蓝色的 Pet-3-glc 螯合物则迅速分解。这些结果表明，花色苷-金属螯合物通过果胶结构的溶解是开发水溶性天然蓝色食用色素的一种有前途的选择。
