Department of Food Quality & Chemistry of Natural Products, Mediterranean Agronomic Institute of Chania (M.A.I.Ch.), International Centre for Advanced Mediterranean Agronomic Studies (CIHEAM), P.O. Box 85, 73100 Chania, Greece.
Green Processes & Biorefinery Group, Department of Food Science & Nutrition, School of Agricultural Sciences, University of Thessaly, N. Temponera Street, 43100 Karditsa, Greece.
Int J Mol Sci. 2024 Jul 17;25(14):7820. doi: 10.3390/ijms25147820.
Olive leaves (OLLs) are an exceptional bioresource of natural polyphenols with proven antioxidant activity, yet the applicability of OLL extracts is constrained by the relatively high polarity of the major polyphenols, which occur as glycosides. To overcome this limitation, OLLs were subjected to both hydrothermal and ethanol organosolv treatments, fostered by acid catalysis to solicit in parallel increased polyphenol recovery and polyphenol modification into simpler, lower-polarity substances. After an initial screening of natural organic acids, oxalic acid (OxAc) was found to be the highest-performing catalyst. The extraction behavior using OxAc-catalyzed hydrothermal and ethanol organosolv treatments was appraised using kinetics, while treatment optimization was accomplished by deploying response-surface methodology. The comparative assessment of the composition extracts produced under optimal conditions of residence time and temperature was performed with liquid chromatography-tandem mass spectrometry and revealed that OLLs treated with 50% ethanol/1.5% HCl suffered extensive oleuropein and flavone glycoside hydrolysis, affording almost 23.4 mg hydroxytyrosol and 2 mg luteolin per g dry weight. On the other hand, hydrothermal treatment with 5% OxAc provided 20.2 and 0.12 mg of hydroxytyrosol and luteolin, respectively. Apigenin was in all cases a minor extract constituent. The study presented herein demonstrated for the first time the usefulness of using a natural, food-grade organic acid to perform such a task, yet further investigation is needed to maximize the desired effect.
橄榄油橄榄叶（OLLs）是一种具有抗氧化活性的天然多酚的特殊生物资源，但由于主要多酚以糖苷形式存在，相对较高的极性限制了 OLL 提取物的应用。为了克服这一限制，通过酸催化促进 OLL 进行水热处理和乙醇有机溶剂处理，以并行提高多酚回收率和多酚修饰成更简单、低极性的物质。在对天然有机酸进行初步筛选后，发现草酸（OxAc）是表现最好的催化剂。使用 OxAc 催化的水热处理和乙醇有机溶剂处理评估了提取行为动力学，通过响应面法完成了处理优化。通过液相色谱-串联质谱法对在最佳停留时间和温度条件下产生的提取物组成进行了比较评估，结果表明，用 50%乙醇/1.5% HCl 处理的 OLL 经历了大量的橄榄苦苷和黄酮糖苷水解，每克干重提供近 23.4 毫克羟基酪醇和 2 毫克木犀草素。另一方面，用 5% OxAc 进行水热处理分别提供了 20.2 和 0.12 毫克羟基酪醇和木犀草素。芹菜素在所有情况下都是次要的提取物成分。本文首次证明了使用天然、食品级有机酸来完成此类任务的有效性，但需要进一步研究以最大限度地发挥预期效果。
