Troup Gordon J, Navarini Luciano, Suggi Liverani Furio, Drew Simon C
School of Physics, Monash University, Victoria, 3800, Australia.
illycaffé Spa, via Flavia 110, 34147, Trieste, Italy.
PLoS One. 2015 Apr 9;10(4):e0122834. doi: 10.1371/journal.pone.0122834. eCollection 2015.
The roasting of coffee beans generates stable radicals within melanoidins produced by non-enzymatic browning. Roasting coffee beans has further been suggested to increase the antioxidant (AO) capacity of coffee brews. Herein, we have characterized the radical content and AO capacity of brews prepared from Coffea arabica beans sourced directly from an industrial roasting plant. In-tact beans exhibited electron paramagnetic resonance signals arising from Fe3+, Mn2+ and at least three distinct stable radicals as a function of roasting time, whose intensity changed upon grinding and ageing. In coffee brews, the roasting-induced radicals were harboured within the high molecular weight (> 3 kD) melanoidin-containing fraction at a concentration of 15 nM and was associated with aromatic groups within the melanoidins. The low molecular weight (< 3 kD) fraction exhibited the highest AO capacity using DPPH as an oxidant. The AO activity was not mediated by the stable radicals or by metal complexes within the brew. While other non-AO functions of the roasting-induced radical and metal complexes may be possible in vivo, we confirm that the in vitro antiradical activity of brewed coffee is dominated by low molecular weight phenolic compounds.
咖啡豆烘焙会在非酶褐变产生的类黑素中生成稳定自由基。进一步研究表明，烘焙咖啡豆可提高咖啡冲泡液的抗氧化（AO）能力。在此，我们对直接取自一家工业烘焙厂的阿拉比卡咖啡豆冲泡液的自由基含量和AO能力进行了表征。完整的咖啡豆表现出由Fe3+、Mn2+以及至少三种不同稳定自由基产生的电子顺磁共振信号，这些信号强度随烘焙时间变化，且在研磨和陈化后发生改变。在咖啡冲泡液中，烘焙诱导产生的自由基存在于高分子量（>3 kD）含类黑素部分，浓度为15 nM，且与类黑素中的芳香基团相关。以DPPH作为氧化剂时，低分子量（<3 kD）部分表现出最高的AO能力。冲泡液中的AO活性并非由稳定自由基或金属络合物介导。虽然烘焙诱导产生的自由基和金属络合物在体内可能具有其他非AO功能，但我们证实，冲泡咖啡的体外抗自由基活性主要由低分子量酚类化合物主导。
