Near-infrared reflectance and Fourier transform infrared analysis of instant coffee mixtures

Abstract

Determination of the actual coffee content of coffee mixtures by wet analytical methods is lengthy and tedious. An alternative method was used, where coffee mixtures were prepared from instant coffee and instant coffee substitute within a range of 0–100% of actual coffee, 0–28.78 mg g^–1 of caffeine and 0–25.77 mg g^–1 of chlorogenic acid. The actual coffee, caffeine and chlorogenic acid contents were determined by near-infrared reflectance (NIR) and Fourier transform infrared (FT–IR) spectroscopic methods. Calibration was used to find the relationship between the spectra obtained and the coffee, caffeine and chlorogenic acid content. The integrated intensity in the range of 1900–1500 cm^–1 in the analytical infrared region was recorded and values estimated by use of multiple linear regression and the partial least squares (PLS) method, in the case of NIR measurements, provided the basis for the calculations. The developed FT–IR and NIR methods were found to be reliable, rapid and exact for determining the actual coffee, caffeine and chlorogenic acid content of instant coffee mixtures within an acceptable level of accuracy.