Fu Boqiang, Li Huan, Wang Xiaoru, Lee Frank S C, Cui Shufen
Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, China.
J Agric Food Chem. 2005 Sep 21;53(19):7408-14. doi: 10.1021/jf051258h.
Five different flavonoids were isolated from licorice after multistep chromatographic fractionation. The aim was to identify and characterize active components in licorice responsible for antibrowning activities and to seek new tyrosinase inhibitors for applications as antibrowning and depigmenting agents in the food and cosmetic industries. The isolated flavonoids were identified as liquiritin, licuraside, isoliquiritin, liquiritigenin (from Glycyrrhiza uralensis Fisch.), and licochalcone A (from Glycyrrhiza inflate Bat.) by UV, MS, (1)H NMR, and (13)C NMR analyses. The inhibitory potencies and capacities of these flavonoids toward monophenolase activity of mushroom tyrosinase were investigated. The IC(50) values of licuraside, isoliquiritin, and licochalcone A for monophenolase activity were 0.072, 0.038, and 0.0258 mM, respectively. A study of the mechanisms of monophenolase inhibition by these flavonoids indicated that they are all competitive inhibitors. Different from the above flavonoids, no inhibitory activity was observed for liquiritin, whereas liquiritigenin activated the monophenolase activity as a cofactor. The inhibitory effect of licuraside, isoliquiritin, and licochalcone A on diphenolase activity with l-DOPA as the substrate was much lower than those with l-tyrosine. Results suggest that licuraside, isoliquiritin, and licochalcone A have the high potential to be further developed into effective antibrowning and depigmenting agents.
经过多步色谱分离，从甘草中分离出了五种不同的黄酮类化合物。目的是鉴定和表征甘草中具有抗褐变活性的活性成分，并寻找新的酪氨酸酶抑制剂，以应用于食品和化妆品行业作为抗褐变和色素沉着剂。通过紫外光谱、质谱、¹H核磁共振和¹³C核磁共振分析，将分离出的黄酮类化合物鉴定为甘草苷、甘草糖苷、异甘草苷、甘草素（来自乌拉尔甘草）和光甘草定（来自胀果甘草）。研究了这些黄酮类化合物对蘑菇酪氨酸酶单酚酶活性的抑制效力和能力。甘草糖苷、异甘草苷和光甘草定对单酚酶活性的IC₅₀值分别为0.072、0.038和0.0258 mM。对这些黄酮类化合物抑制单酚酶的机制研究表明，它们都是竞争性抑制剂。与上述黄酮类化合物不同，未观察到甘草苷有抑制活性，而甘草素作为辅因子激活了单酚酶活性。以L-多巴为底物时，甘草糖苷、异甘草苷和光甘草定对双酚酶活性的抑制作用远低于以L-酪氨酸为底物时。结果表明，甘草糖苷、异甘草苷和光甘草定具有进一步开发成为有效的抗褐变和色素沉着剂的巨大潜力。
