Abstract: "Huaimi", refering to the buds of pagoda tree (Styphnolobium japonicum), is native to China, and currently mainly distributed in North China and the Loess Plateau region. During the Ming and Qing dynasties, it was widely used as a dye in textile dyeing. The buds of pagoda tree are rich in flavonoids, such as rutin and quercetin, and the main active ingredient is rutin. In order to obtain a bright yellow color, ancient dyers usually boiled or fried buds of pagoda tree at high temperatures. This process prevents rutin from being hydrolyzed into quercetin, thereby  rendering the dyed color on fabrics more vibrant. In ancient China, yellow was always closely associated with imperial authority, symbolizing supreme authority and being one of the most revered colors by the ancients. Therefore, yellow dyes are often detected in ancient textiles, and buds of pagoda tree is one of the common dyes. Before using detection techniques to analyze textile dyes, it is necessary to extract and peel the dyes from the textiles. So selecting an appropriate extraction method is particularly important. There are various methods for extracting dyes from silk fabrics, among which the most widely used is heating with hydrochloric acid. However, this method easily hydrolyzes the glycoside components in the dyes, resulting in the loss of information sources related to the dyes, especially for flavonoid dyes as most of them contain many glycoside compounds. Therefore, it is important to use appropriate extraction methods to obtain more information about the dyes.
This article aims to explore the extraction method and process optimization for silk fabrics dyed with buds of pagoda tree. Two extraction methods were used: pyridine (pyridine aqueous solution/0.5 mol/L moxalic acid) and methanol(10 mmol/L ethylenediaminetetraacetic acid disodium/acetonitrile/methanol aqueous solution). The pigments were extracted by heating and nitrogen blowing. Single-factor experiments were designed and conducted to screen three factors affecting extraction: temperature, time, and solvent volume fraction. Furthermore, the extraction process was optimized using the response surface method (RSM).
The results showed that the optimal process conditions for the pyridine extraction method were an extraction temperature of 56.9 ℃, an extraction time of 29.6 min, and a pyridine volume fraction of 42.2 %. The predicted and actual optimal absorbance values were consistent, at 0.940 and 0.939, respectively. For the methanol extraction method, the optimal process conditions were  an extraction temperature of 61.6 ℃, an extraction time of 25.9 min, and a methanol volume fraction of 49.6%. The predicted and actual optimal absorbance values were also consistent, at 0.784 and 0.780, respectively. RSM provides a simple and reliable optimization method for dye extraction. The pyridine and methanol extraction methods can obtain the main dye components and glycoside compounds of buds of pagoda tree, which can provide more compound information. This experiment can provide reference for the extraction of buds of pagoda tree and other flavonoid dyes from silk fabrics.

Key words: silk fabrics, natural dyes, pagoda tree buds, flavonoid pigments, pigments extraction, RSM

摘要： 为了提高槐米染色丝织品中黄酮类色素萃取效率，采用了吡啶和甲醇2种萃取方法，并利用单因素实验结合响应面法(Response surface method，RSM)对萃取工艺进行优化。结果表明：吡啶萃取法的最佳工艺是萃取温度56.9 ℃，萃取时间29.6 min，吡啶体积分数42.2%；最佳吸光度预测值和实际值为0.940和0.939。甲醇萃取法的最佳工艺是萃取温度61.6 ℃，萃取时间25.9 min，甲醇体积分数49.6%；最佳吸光度预测值和实际值为0.784和0.780。RSM为色素萃取提供了可靠的优化方法，通过这2种萃取法能够得到槐米的主要色素成分及糖苷类化合物，可以获取更多的化合物信息。研究结果可为丝织品中的黄酮类色素萃取提供参考。

关键词: 丝织品, 天然染料, 槐米, 黄酮类色素, 色素萃取, 响应面法