Department of Physical and Analytical Chemistry, Uppsala University, Uppsala, Sweden.
Anal Chim Acta. 2012 Feb 24;716:40-8. doi: 10.1016/j.aca.2011.04.038. Epub 2011 Apr 27.
Experiments with birch bark samples have been carried to enable a distinction between extraction and degradation effects during pressurised hot water extraction. Two samples, E80 and E180, contained birch bark extracts obtained after extraction at 80 and 180°C for up to 45 min, respectively. Two other samples, P80 and P180, were only extracted for 5 min at the two temperatures and were thereafter filtered and hydrothermally treated at 80 and 180°C, respectively. During the latter treatment, samples were collected at different times to assess the stability of the extracted compounds. An offline DPPH (2,2-diphenyl-1-picrylhydrazyl) assay, as well as a high performance liquid chromatographic separation coupled to an electrochemical detector, were used to determine the antioxidant capacity of the processed samples. The results obtained with the different techniques were compared to assess the yield of the extraction and degradation processes. In addition, an online hyphenated system comprising high performance liquid chromatography coupled to diode-array; electrochemical; and tandem mass spectrometric detection (HPLC-DAD-ECD-MS/MS) was used to study the compositions of the extracts in more detail. The results for the samples processed at 80°C showed that the extraction reached a steady-state already after 5 min, and that the extracted compounds were stable throughout the entire extraction process. Processing at 180°C, on the other hand, gave rise to partly degraded extracts with a multitude of peaks in both the diode array and electrochemical detectors, and a higher antioxidant capacity compared to for the extracts obtained at 80°C. It is concluded that HPLC-DAD-ECD is a more appropriate technique for the determination of antioxidants than the DPPH assay. The mass spectrometric results indicate that one of the extracted antioxidants, catechin, was isomerised to its diastereoisomers; (+)-catechin, (-)-catechin, (+)-epicatechin, and (-)-epicatechin.
已经进行了桦树皮样本的实验，以区分加压热水提取过程中的提取和降解效应。两个样本 E80 和 E180 分别包含在 80 和 180°C 下提取长达 45 分钟后获得的桦树皮提取物。另外两个样本 P80 和 P180 仅在两个温度下提取了 5 分钟，然后分别在 80 和 180°C 下过滤和水热处理。在后一种处理过程中，收集了不同时间的样品以评估提取化合物的稳定性。离线 DPPH（2,2-二苯基-1-苦基肼基）测定法以及高效液相色谱分离与电化学检测器耦合，用于测定处理样品的抗氧化能力。使用不同技术获得的结果进行了比较，以评估提取和降解过程的产率。此外，使用在线联用法，包括高效液相色谱与二极管阵列；电化学；和串联质谱检测（HPLC-DAD-ECD-MS/MS）更详细地研究了提取物的组成。在 80°C 处理的样品的结果表明，提取在 5 分钟后已经达到稳定状态，并且提取的化合物在整个提取过程中都是稳定的。另一方面，在 180°C 下处理会导致部分降解的提取物在二极管阵列和电化学检测器中出现多个峰，并且抗氧化能力比在 80°C 下获得的提取物更高。结果表明，HPLC-DAD-ECD 比 DPPH 测定法更适合测定抗氧化剂。质谱结果表明，一种提取的抗氧化剂儿茶素被异构化为其非对映异构体；（+）-儿茶素、（-）-儿茶素、（+）-表儿茶素和（-）-表儿茶素。
