GC/MS method to quantify bioavailable phenolic compounds and antioxidant capacity determination of plasma after acute coffee consumption in human volunteers.

Coffee, a source of chlorogenic acids (CGAs), is recognized for preventing chronic diseases associated with oxidative stress. Therefore, sensitive, selective and easy access methods for the determination of the bioavailability and antioxidant function in vivo are required in clinical studies. The aim of this work was to validate a GC/MS method to quantify caffeic acid (CA) and ferulic acid (FA) and to apply different methodologies to determine the antioxidant capacity of plasma after the acute consumption of 420mg of CGAs provided by 400mL of coffee. The intervention was performed in 20 adults (6 men and 14 women) with a mean±SD age of 35.7±9.0 and body mass index of 22.1±1.6kg who were assigned to 2 groups: a control group and a group that consumed coffee. The validated analytical GC/MS method was exact, precise and selective. The selected derivatizing reagent was N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide with 1% tertbutyldimethylchlorosilane (MTBSTFA+1% TBDMSCl). The method was reproducible, and the limit of detection (LOD) was 3nM for CA and 5nM for FA. CA and FA were detected in plasma 1h after coffee intake and were undetectable in the control group. Compared to the baseline values, the antioxidant capacity of plasma significantly increased when it was measured by ferric reducing antioxidant power (FRAP) (6.67%; P<0.001) and by oxygen radical absorbance capacity (ORAC) (7.16%; P<0.05). The in vitro and ex vivo experiments on plasma with CA and FA showed a significant increase of the antioxidant activity (P<0.05) as well as delay of LDL oxidation (P<0.001). The method validated by GC/MS was proposed as an alternative for evaluating the bioavailability of ACG after acute coffee intake. The need for in vitro methodologies was demonstrated to determine the antioxidant activity.