Spectrophotometric method for quantification of kahweol in coffee

The diterpene kahweol, a component of the unsaponifiable matter of coffee oil, has anticarcinogenic and antioxidant properties. Kahweol is specific to Coffea arabica, so it can be used to discriminate between coffee species. Chromatographic or infrared techniques are usually required for the evaluation of kahweol. The objective of this study was to develop a methodology to quantify kahweol based in colorimetric reactions and spectrophotometric measurements. The best extraction conditions were achieved by direct saponification of roasted and ground coffees, extraction with MTBE, cleaning the extract with water, reaction of the extract with KI, dilution with HAc 50% and absorbance analysis at 620 nm for quantification. This method demonstrated good precision (RSD below 5%) considering different extractions and intraday repeatability. Linearity was also observed (R2 = 0.996, p ≤ 0.05), with low limits of detection (5.16 mg 100 g−1) and quantification (17.2 mg 100 g−1). Kahweol contents were assessed at similar levels to those obtained using a standard HPLC methodology, and a good recovery was observed (116%).