Multivariate optimization of residual caffeine extraction from decaffeinated coffee

This study evaluated techniques of extraction of caffeine from decaffeinated coffee samples for application in quality control of industrial decaffeination processes. The extraction was studied using two methods, an aqueous one and another through liquid-liquid partition with chloroform. The objective was to extract the maximum amount of caffeine with the minimum of interference from the matrix and with good repeatability of extraction. After comparing the aqueous extraction and extraction with chloroform, a 23 factorial design was performed to optimize the liquid-liquid extraction. The parameters analyzed in the factorial design were the solvent:sample ratio, extraction time, and filtration or not after extraction. The optimum extraction point was defined using the amount of caffeine extracted as the response factor. Caffeine levels were quantified by capillary electrophoresis according to an analytical method previously optimized and validated. The best extraction condition was achieved through liquid-liquid partition with chloroform, using 30 mL of solvent, 7 min of agitation, and without filtration. This condition showed good repeatability (2.8%, n = 7), recovery of 96.7-107.4%, and removal of interfering matrix. The method was applied to samples of decaffeinated roasted and ground coffee, and instant coffee.