Content of 4(5)-methylimidazole, caffeine and chlorogenic acid in commercial coffee brands

Abstract

Content of 4(5)-methylimidazole (4-MeI), caffeine and chlorogenic acid in commercial coffee brands were determined using high-performance liquid chromatography (HPLC) with UV DAD and MS detectors. Positive ion ESI mass spectra of the 4-MeI standard yielded intense signals corresponding to [M+H]+ (83.0604) and [2M+H]+ ions (165.1115). Also, adducts of 4-MeI with acetonitrile from mobile were detected - [M+ACN]+ ions (124.0849). The LOD of 2.5 ng mL-1 and LOQ of 8.4 ng.mL-1 were calculated according to the following formulas: LOD = 3.SD/S, and LOQ = 10.SD/S, where S is the slope of the calibration curve and SD is the standard deviation of the noise. The caffeine content was compared to the results of the standard addition, 1st derivative and liquid-liquid extraction spectrophotometry. 4-MeI was in tens µg g-1 in the Vietnamese coffees while in units µg.g-1 in all Czech and Brazilian coffees (<2.4 µg.g-1 and <4.9 µg.g-1, respectively). The results for caffeine were within the documented range (0.31 - 2.20%) in all coffee samples. The lower content of caffeine and chlorogenic acid was observed in Vietnamese coffees. All the methods used for determination of caffeine in the Czech and Brazilian coffees gave acceptable precision and accuracy. However, there were significant differences in the results in Vietnamese coffees. The caffeine extractability (100 °C, 3 min brewing) almost reached 100% in Czech and Brazilian coffees, while it was less than 90% in Vietnamese coffees. The Czech and Brazilian coffees tend to produce more caffeine in brews than the Vietnamese coffee because of the different composition of blends and the particle size degree.  

Keywords

• coffee
• spectrophotometric methods
• HPLC
• caffeine extractability