A simple adsorption process allowing a high retention of polyphenols contained in extracts of onion skin with ethanol/water volume ratio going up to 80/20 is described. We show that the straightforward processing of the extracts is possible, even at low water content, by using quercetin-molecularly imprinted (Q-MIP) adsorbents synthesized with 4-vinylpyridine (4VP) as the functional monomer. The favorable interactions between the pyridyl functional groups of 4VP and the polyphenols, as well as the improved binding site accessibility introduced by molecular imprinting, are at the source for the good performance observed with the Q-MIPs. The usefulness of the Q-MIPs in onion skin polyphenols purification, fractionation and concentration is demonstrated with few sorption/desorption steps and considering sonicated, Soxhlet and supercritical CO2 extracts. Polyphenol retention of c.a. 88% is possible with Q-MIPs (7% with non-tailored adsorbents) when directly processing ethanol/water 80/20 extracts. Protocatechuic acid and other very hydrophilic molecules (such as simple sugars) were readily removed from the extracts, leaving fractions containing mostly quercetin and quercetin derivatives. Polyphenol recovery higher than 90% (measured with quercetin) and concentration factors up to 34 times were observed with the Q-MIPs.

中文翻译：

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用槲皮素分子印迹吸附剂处理洋葱皮提取物，适用于各种含水量

描述了一种简单的吸附过程，可以高保留洋葱皮提取物中的多酚，乙醇/水的体积比高达 80/20。我们表明，通过使用以 4-乙烯基吡啶 (4VP) 作为功能单体合成的槲皮素分子印迹 (Q-MIP) 吸附剂，即使在低含水量的情况下，也可以直接处理提取物。4VP 的吡啶基官能团与多酚之间的有利相互作用，以及分子印迹引入的改进的结合位点可及性，是使用 Q-MIP 观察到的良好性能的来源。Q-MIP 在洋葱皮多酚纯化、分馏和浓缩中的有用性通过很少的吸附/解吸步骤和考虑超声处理得到证明，索氏提取和超临界 CO2 提取。当直接处理乙醇/水 80/20 提取物时，Q-MIP 的多酚保留率可能达到约 88%（使用非定制吸附剂时为 7%）。原儿茶酸和其他亲水性很强的分子（如单糖）很容易从提取物中去除，留下的部分主要含有槲皮素和槲皮素衍生物。使用 Q-MIP 观察到多酚回收率高于 90%（用槲皮素测量）和高达 34 倍的浓度因子。