Chemical composition of Galla chinensis extract and the effect of its main component（s） on the prevention of enamel demineralization in vitro

To determine the chemical composition of Galla chinensisextract （GCE） by several analysis techniques and to compare the efficacy of GCE and its main component（s） in inhibition of enamel demineralization, for the development of future anticaries agents, main organic composition of GCE was qualitatively determined by liquid chromatography-time of flight-mass spectrometry （LC-TOF-MS） and quantified by high-performance liquid chromatography-diode array detector （HPLC-DAD）. Inorganic ions were tested by inductively coupled plasma-atomic emission spectroscopy and F was especially measured by ion chromatography. Then, bovine enamel blocks were randomly divided into four treatment groups and were subjected to a pH-cycling regime for 12 times. Each cycle included 5-min applications with one of four treatments： 4g.L-1 GCE solution, 4g.L-1 gallic acid （GA） solution, I g.L-1 NaF solution （positive control）, deionized water （DDW, negative control）, and then 60-min application in pH 5.0 acidic buffer and 5-min application in neutral buffer. Acidic buffers were retained for calcium analysis. The main organic composition of GCE were GA and its isomer, and, to a lesser extent, small molecule gallotannins. The content of GA in GCE was 71.3%±0.2% （w/w）. Inorganic ions were present in various amounts, of which Ca was （136±2.82） μg.g-1, and Zn was （6.8±0.1） μg.g-1. No F was detected in GCE. in pH cycling, GA showed an effect similar to GCE in inhibiting enamel demineralization （P〉0.05）. GA was found to be the main effective, demineralization inhibiting component of GCE and could be a promising agent for the development of anticaries agents.