P.P. Nhan’s scientific contributions

The stimulating effect of coffee is mainly depended on caffeine availability in products. Caffeine levels in grains of two coffee species, Coffea arabica and Coffea robusta, have been quantified via the maximal absorbance of standard caffeine at 288 nm. Three popular coffee brands in Vietnam were selected for quality assessment based on the qualitative information printed on their labels. Caffeine level in C. robusta is always higher than that of C. arabica at any time durations and temperatures of extraction. Best combination between time and temperature for caffeine extraction is 15 min and 90°C or 100°C. About 90% of caffeine has been removed from coffee powder by routine percolated. The extracted caffeine is tightly correlated with extracting sequence by the equation of y = 1.7647x -1.5023 with R 2 = 0.9963. The chosen coffee products have higher caffeine contents, at least 2.5 times than those appeared on their labels.