Chemical and Bioprocess Engineering Department, School of Engineering, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, P.O. Box 306, Santiago 7820436, Chile.
Escuela de Ingeniería Agroindustrial, Universidad Nacional de Moquegua, Prolongación calle Ancash s/n, Moquegua 18001, Peru.
Biomolecules. 2020 Mar 20;10(3):474. doi: 10.3390/biom10030474.
Glycerol is a co-solvent for water extraction that has been shown to be highly effective for obtaining polyphenol extracts under atmospheric conditions. However, its efficacy under subcritical conditions has not yet been studied. We assessed different water-glycerol mixtures (15%, 32.5%, and 50%) in a hot pressurized liquid extraction system (HPLE: 10 MPa) at 90 °C, 120 °C, and 150 °C to obtain extracts of low molecular weight polyphenols from grape pomace. Under the same extraction conditions, glycerol as a co-solvent achieved significantly higher yields in polyphenols than ethanol. Optimal extraction conditions were 150 °C, with 32.5% glycerol for flavonols and 50% for flavanols, stilbenes, and phenolic acids. Considering gallic acid as a model molecule, computational chemistry calculations were applied to explain some unusual extraction outcomes. Furthermore, glycerol, methanol, ethanol, and ethylene glycol were studied to establish an incipient structure-property relationship. The high extraction yields of gallic acid obtained with water and glycerol solvent mixtures can be explained not only by the additional hydrogen bonds between glycerol and gallic acid as compared with the other alcohols, but also because the third hydroxyl group allows the formation of a three-centered hydrogen bond, which intensifies the strongest glycerol and gallic acid hydrogen bond. The above occurs both in neutral and deprotonated gallic acid. Consequently, glycerol confers to the extraction solvent a higher solvation energy of polyphenols than ethanol.
甘油是一种水提取的共溶剂，已被证明在常压下提取多酚提取物非常有效。然而，其在亚临界条件下的效果尚未得到研究。我们在热加压液体萃取系统（HPLE：10 MPa）中评估了不同的水-甘油混合物（15%、32.5%和 50%）在 90°C、120°C 和 150°C 下，从葡萄渣中提取低分子量多酚提取物。在相同的提取条件下，甘油作为共溶剂在多酚提取方面的产率明显高于乙醇。最佳提取条件为 150°C，其中 32.5%的甘油用于黄酮醇，50%的甘油用于黄烷醇、白藜芦醇和酚酸。考虑到没食子酸作为模型分子，应用计算化学计算来解释一些不寻常的提取结果。此外，还研究了甘油、甲醇、乙醇和乙二醇，以建立初步的结构-性质关系。与其他醇相比，水和甘油溶剂混合物提取没食子酸的高提取率不仅可以用甘油和没食子酸之间形成的额外氢键来解释，还可以用第三个羟基允许形成三中心氢键来解释，这加强了最强的甘油和没食子酸氢键。上述情况既发生在中性没食子酸中，也发生在去质子化的没食子酸中。因此，甘油赋予提取溶剂比乙醇更高的多酚溶解能。
