Murtaza Ayesha, Muhammad Zafarullah, Iqbal Aamir, Ramzan Rabia, Liu Yan, Pan Siyi, Hu Wanfeng
Key Laboratory of Environment Correlative Dietology, Ministry of Education, College of Food Science and Technology, Huazhong Agriculture University, Wuhan, China.
Front Chem. 2018 Jun 5;6:203. doi: 10.3389/fchem.2018.00203. eCollection 2018.
This study investigated the effects of heat treatment after purification on dissociation, aggregation, and structural modification of polyphenol oxidase (PPO) activity from apple () juice. PPO activity at the 70°C for 10 min was still activated and drastically decreased since 20-60 min with catechol and pyrogallol as substrate. Moreover, spectral results of fluorescence and circular dichroism (CD) indicated that increasing temperature for shorter and longer durations can cause reorganization of the secondary structure of PPO and demolished the native configuration of PPO respectively. Compared with native PPO, all thermally treated PPO showed reduced activity with gradually increasing particle size shift toward section III of some fully assembled proteins treated at 70°C for 10 min (2,670 nm). Polyacrylamide gel electrophoresis (PAGE) analysis also exhibited the increase in protein content at the 70°C for 10 min with molecular size 35 kDa (7.7 ± 0.016c). Hence, thermally treated juice subjected to purification at high temperature for a short time could induce the aggregation of protein and is not really effective for PPO inactivation. For PPO, higher degree of long duration can induce the inactivation of the enzyme after processing.
本研究调查了纯化后热处理对苹果汁中多酚氧化酶（PPO）活性的解离、聚集及结构修饰的影响。以邻苯二酚和连苯三酚为底物时，70°C处理10分钟后PPO活性仍被激活，但在20 - 60分钟内急剧下降。此外，荧光光谱和圆二色光谱（CD）结果表明，较短和较长时间的升温分别会导致PPO二级结构的重新组织和破坏PPO的天然构象。与天然PPO相比，所有热处理的PPO活性均降低，随着粒径逐渐增大，一些在70°C处理10分钟的完全组装蛋白向III区移动（2670 nm）。聚丙烯酰胺凝胶电泳（PAGE）分析还显示，70°C处理10分钟后，分子大小为35 kDa的蛋白质含量增加（7.7±0.016c）。因此，短时间高温纯化的热处理果汁会诱导蛋白质聚集，对PPO失活并非真正有效。对于PPO而言，较长时间的高温处理会导致酶在处理后失活。
