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  • Stable radical content and anti-radical activity of roasted Arabica coffee: from in-tact bean to coffee brew.

Stable radical content and anti-radical activity of roasted Arabica coffee: from in-tact bean to coffee brew.

PloS one (2015-04-10)
Gordon J Troup, Luciano Navarini, Furio Suggi Liverani, Simon C Drew
ABSTRACT

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.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Diethylenetriaminepentaacetic acid, for complexometry, ≥99.0%
Sigma-Aldrich
Diethylenetriaminepentaacetic acid, ≥98% (titration)
Sigma-Aldrich
Diethylenetriaminepentaacetic acid, ≥99% (titration)
Sigma-Aldrich
1,1-Diphenyl-2-picrylhydrazine, 97%
Sigma-Aldrich
2,2-Diphenyl-1-picrylhydrazyl
Supelco
Anabasine-d4 hydrochloride solution, 100 μg/mL in methanol (as free base), ampule of 1 mL, certified reference material, Cerilliant®