1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) is widely used as a crosslinker for fluorescence labeling of protein in the fields of biochemistry and food analysis. Many natural polysaccharides often contain some proteins or peptides that are very low in content but play a vital role in their biological function as well as technical applications. Determination of these low-content proteinaceous matters requires a highly sensitive and selective method. In this study, a methodological approach for investigations of the presence of proteinaceous material over the molar mass distribution (MD) of polysaccharides was developed using gum acacia (GA) as a model polysaccharide. EDC fluorescence-labeling method was modified by changing the pH (7, 9, and 11) of the solution for the analysis of low-content protein in food materials. Fluorescence spectroscopy and asymmetrical flow field-flow fractionation (AF4) were employed for characterizing the labeling efficiency and physiochemical properties of unlabeled and fluorescence-labeled GA. AF4 provided molar mass (M) and the radius of gyration (r_G) of arabinogalactan (AG) and arabinogalactan protein complex (AGP) and determined the presence of proteinaceous matter over the MD. The labeling efficiencies of GA at pH 7, 9, and 11 determined by fluorescence spectroscopy were 56.5, 68.4, and 72.0%, respectively, with an increment of 15.5% when pH was increased from 7 to 11. The modified EDC fluorescence-labeling method allows highly sensitive and selective analysis of low-content proteinaceous matters and their distribution in natural polysaccharides.

Graphical abstract

中文翻译：

---

使用不对称流场-流分馏结合多个检测器改进 EDC 方法以提高阿拉伯树胶中低含量蛋白质的标记效率和表征

1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) 在生物化学和食品分析领域广泛用作蛋白质荧光标记的交联剂。许多天然多糖通常含有一些蛋白质或肽，它们的含量非常低，但在其生物学功能和技术应用中起着至关重要的作用。这些低含量蛋白质物质的测定需要高度灵敏和选择性的方法。在这项研究中，一种研究蛋白质物质在摩尔质量分布（MD) 的多糖是使用阿拉伯树胶 (GA) 作为模型多糖开发的。通过改变溶液的 pH 值（7、9 和 11）改进了 EDC 荧光标记方法，用于分析食品材料中的低含量蛋白质。荧光光谱和不对称流场-流分馏 (AF4) 用于表征未标记和荧光标记 GA 的标记效率和理化性质。AF4 提供了阿拉伯半乳聚糖 (AG) 和阿拉伯半乳聚糖蛋白复合物 (AGP) 的摩尔质量 ( M ) 和回转半径 ( r _G )，并确定了MD上蛋白质物质的存在. 荧光光谱法测定 GA 在 pH 7、9 和 11 的标记效率分别为 56.5、68.4 和 72.0%，当 pH 从 7 增加到 11 时增加了 15.5%。改进的 EDC 荧光标记方法允许对低含量蛋白质物质及其在天然多糖中的分布进行高灵敏度和选择性分析。

图形概要