2011 Volume 28 Issue 1 Pages 23-
A flow-injection analysis (FIA) procedure with colorimetric detection was developed, to determine the total polyphenol content (TPP) in coffee brews with no need for sample work-up. A comparison of three different officially accepted colorimetric methods was performed and the Folin-Ciocalteu reaction was found to be the most suitable assay with respect to sensitivity, selectivity, lack of matrix effects and cost. Furthermore, the FIA setup adopted here was characterized by its simple experimental design, relatively inexpensive equipment and for providing results that are excellent in view of rapidity, accuracy and precision. FIA key parameters were optimised for sensitivity, linearity, working range and matrix effects, and calibrated against gallic, caffeic, ferulic and tannic acid equivalents. The method was successfully tested against false-positive adsorptions from non-polyphenol components. The method was applied first to brews from two different C. Arabica (Coffea arabica L.) and C. Robusta (Coffea canephora var. robusta L) coffees (light roast). Robusta showed 25% higher TPP content compared to Arabica. Secondly, coffees roasted to three different roast degrees, each along three different time-temperature roasting profiles, were compared: High-temperature with short roasting times showed higher TPP content in the brew than low-temperature with longer roasting times, an observation that indicates the potential for optimising the roasting process to increase polyphenol content.
