Effects of thermal treatments on 10 major phenolics and their antioxidant contributions in Acer truncatum leaves and flowers

This study aimed to investigate effects of thermal treatments on major phenolics and their antioxidant contributions in Acer truncatum leaves and flowers (ATL and ATF, respectively). With ultra performance liquid chromatography-diode array detector-quadrupole time-of-flight-mass spectrometer/mass spectrometer, phenolic compositions of ATF were first characterized and compared with those of ATL. An optimized high performance liquid chromatography fingerprint was then established, and 10 major phenolics existing in both ATL and ATF were quantified. Gallic acid derivatives and flavonol-3-O-glycosides were found to be their dominant phenolic constituents, with the former being key constituents which was affected by thermal treatments and further influencing the variations of total phenols. Moreover, the mechanism underlining the changes of phenolics in ATL and ATF by the treatments was characterized as a thermolhydrolysis process. During thermal treatments, polymerized gallotannins were hydrolysed to 1,2,3,4,6-pentakis-O-galloyl-β-d-glucose, ethyl gallate and gallic acid, resulting in more than fivefold and twofold increase of their contents in ATL and ATF, respectively. By contrast, contents and antioxidant contributions of flavonol-3-O-glycosides gradually decreased during the process.\absbreak Overall, this is, to our knowledge, the first report on the effects of thermal treatments on phenolics and their antioxidant contributions in ATL and ATF, and the three gallic acid derivatives with potentially higher bioactivity could be efficiently achieved by thermal treatments.