Loo Alvin Eng Kiat, Huang Dejian
Department of Chemistry, National University of Singapore, Republic of Singapore.
J Agric Food Chem. 2007 Nov 28;55(24):9805-10. doi: 10.1021/jf071500f. Epub 2007 Oct 26.
Alpha-amylase inhibitor (alpha-AI) activity of Garcinia mangostana, commonly known as mangosteen, pericarp extracts was studied by assay guided fractionations from lipophilic to hydrophilic using combined solvent extraction and Amberlite XAD2 adsorption chromatography. Neither the lipophilic, xanthone containing fraction, nor the highly polar fraction, which has no affinity on Amberlite XAD2, showed any alpha-AI. The fraction that shows very high inhibitory activity contains primarily polyphenols and can be adsorbed on Amberlite XAD2. The IC50 of 5.4 microg/mL of this fraction is comparable to that of acarbose, a prescribed alpha-AI used in the control of type II diabetes, at 5.2 microg/mL. Total phenolic content (TPC) of each fraction was measured and the TPC has no correlation with the alpha-AI activity. The lipophilic fraction contains mainly xanthones as revealed by HPLC-MS analysis. Colorimetric analysis coupled with UV-vis and IR spectroscopic analysis demonstrated that the fractions with high alpha-AI activity are primarily oligomeric proanthocyanidins (OPCs) with little gallate moiety. There is also evidence to show that the alpha-AI by these OPCs is not purely by nonspecific protein complexation. Both tannic acid and G. mangostana OPCs precipitate BSA equally well but G. mangostana OPCs are 56 times more effective in inhibiting alpha-amylase.
通过使用组合溶剂萃取和Amberlite XAD2吸附色谱法，从亲脂性到亲水性进行分析导向分级分离，研究了山竹果皮提取物的α-淀粉酶抑制剂（α-AI）活性。既没有亲脂性的含氧杂蒽酮馏分，也没有对Amberlite XAD2没有亲和力的高极性馏分显示出任何α-AI活性。显示出非常高抑制活性的馏分主要含有多酚，并且可以吸附在Amberlite XAD2上。该馏分的IC50为5.4μg/mL，与用于控制II型糖尿病的规定α-AI阿卡波糖的5.2μg/mL相当。测量了每个馏分的总酚含量（TPC），并且TPC与α-AI活性没有相关性。通过HPLC-MS分析表明，亲脂性馏分主要含有氧杂蒽酮。比色分析结合紫外可见和红外光谱分析表明，具有高α-AI活性的馏分主要是低聚原花青素（OPC），几乎没有没食子酸部分。也有证据表明这些OPC的α-AI并非纯粹通过非特异性蛋白质络合作用。单宁酸和山竹OPC对牛血清白蛋白（BSA）的沉淀效果相同，但山竹OPC在抑制α-淀粉酶方面的效果要高56倍。
