The qualitative and quantitative analysis of adulteration in specialty coffee from Tanggamus lampung using UV-visible spectroscopy and chemometrics

In Tanggamus region, Robusta coffee is mainly planted in the mountainous area (more than 600 meters above sea level) resulted in a high quality of Robusta coffee. In 2014, Robusta coffee from Tanggamus region got a certificate of geographic indication from Indonesian government and regarded as one of Indonesian specialty coffee. In ground roasted coffee, it is difficult to discriminate between specialty coffee and normal coffee (non-specialty coffee). To establish a fair trading of specialty coffee from Tanggamus region, it is highly desired to develop an easy and cheap analytical method for specialty coffee authentication. In this research, we utilize UV-visible spectroscopy and chemometrics methods to discriminate specialty coffee from normal coffee both quantitatively and qualitatively. A number of 180 samples of Tanggamus specialty coffee with different adulteration level was prepared. All samples were subjected to an extraction procedure using a hot distilled water. Spectral acquisition was done using a UV-visible spectrometer in the range of 190-1100 nm. Principal component analysis (PCA) and partial least squares (PLS) regression was applied for qualitative and quantitative analysis, respectively. The result of qualitative analysis showed that the samples can be clustered into three groups of adulteration (low, middle and high) using PC1 and PC2 with total 96% of explained variance. The best calibration model was achieved using preprocessed spectra with R2=0.99 and RMSECV=2.08%. The result of prediction was accepted with SEP=2.38% and RPD=7.292.