A study of the bioavailability of green coffee methylxanthines in humans

Abstract

Coffee is a popular beverage consumed worldwide, with stimulant properties due to its high caffeine content. Although coffee has been traditionally consumed after roasting, green coffee beans are richer in bioactive compounds, leading to its introduction as a nutraceutical or as an alternative to roasted coffee. We assessed the bioavailability of caffeine and other methylxantines in humans after consuming a commercially available blend of green and toasted coffee. Healthy men and women (n=12), aged 18-45, non-smoker, non-vegetarian, who presented a BMI 18-25 kg/m2 consumed after an overnight fast one serving of soluble coffee (3.5 g) in 300 mL of hot water. Blood samples were collected at baseline and postprandially at 0.5, 1, 1.5, 2, 3, 4, 5, 6, 8, 9, 10 and 12h. Plasma was immediately separated by centrifugation. Urine samples were collected before intake (t=-2-0h) and at intervals 0-2, 2-5, 5-8, 8-12 and 12-24h after drinking the beverage. Two days before the intervention, methylxanthine rich-foods were restricted from their diets. Plasma and urine samples were analysed by HPLC. Identification and quantification of methylxanthines and methyluric acids was carried out by comparison with standards. As expected, caffeine (CF) was the main metabolite found in plasma, followed by paraxanthine (PX), theophylline (TP) and 1-monomethylxanthine (1-MX), showing the highest absorption 1h after consumption. In urine samples the following analytes were identified: CF, dimethylxanthines [PX, TP and theobromine (TB)], monomethylxanthines (1-, 3- and 7-MX), monomethyluric acid (1-MU) and dimethyluric acids (1,3- 1,7- and 3,7-diMU). We observed that the concentration of all analytes in urine increased along the time, particularly CF and its metabolites PX, 1-MX, 1-MU and 1,7-diMU. It can be concluded that methylxanthines in coffee are highly bioavailable, metabolized and excreted in urine along 24 hours after consumption.