Determination of Trigonelline and Chlorogenic Acid (CGA) Concentration in Intact Coffee Beans by NIR Spectroscopy

Abstract

Trigonelline and chlorogenic acid (CGA) are important quality indicators of coffee. Commonly, trigonelline and CGA concentration are determined using chemical method. This method is time consuming and destructive so it is not suitable for coffee industries which need a fast measurement. The objective of this study was to assess NIR spectroscopy for predicting trigonelline and CGA concentration in intact coffee beans. Coffee beans samples of 96 g (n=100) were placed in a petri dish. The reflectance of samples was measured by FT-NIR spectrometer in the wavelengths of 1000-2500 nm. Subsequently, the trigonelline and CGA content of samples were determined using Liquid Chromatography Mass Spectrometry (LCMS). Spectra data processing such as first and second derivative, multiple scatter correction (MSC), Standard Normal Variate (SNV) and the combination of them were carried out to reduce scattering, to eliminate overlapped absorption bands, and to optimize the best data input in calibration process. After that, these spectra (n=67) were calibrated to chemical data using Partial Least Square (PLS) to find the best calibration models. Then the calibration models were applied to predict trigonelline and chlorogenic acid (CGA) in another set of samples (n=33).  The results showed that NIR spectra data processing of second derivative combined with 4 factors of PLS was the best model for predicting CGA concentration of coffee (r=0.94, CV=2,75%, RPD=2.27). For trigonelline, however, the best model was combination of second derivative and MSC of spectra data processing and 4 factors of PLS (r=0.98, CV=1.63%, RPD=2.98). These results indicated that NIR spectroscopy can be used as a fast and nondestructive method for determining trigonelline and CGA in intact coffee beans accurately.

Keywords:   chlorogenic acid, intact coffee bean, NIRS, PLS, trigonelline