The potential application of portable spectrometer equipped with integrating sphere and PLS-DA method to authenticate Indonesian specialty coffee

In this research, a potential application of using portable spectrometer equipped with an integrating sphere to authenticate Indonesian specialty coffee was described. 20 samples of specialty and normal ground roasted coffee was used as samples. Each sample has about 1.33 gram in weight and particle size of 297 micrometer. Spectral data in the range of 900-1657 nm was acquired in diffuse reflectance mode using a portable fiber optic NIR-Quest InGaAs spectrometer (Ocean Optics, USA) equipped with an integrating sphere (ISP-REF, Ocean Optics, USA) with 1.645 nm interval. The integrating sphere is coated with Spectralon® and installed a built-in tungsten-halogen light source. Partial least squares-discriminant analysis (PLS-DA) was used to classify the samples into two groups: specialty coffee (labelled as 1) and normal coffee (labelled as 0). The result demonstrated that the best PLS-DA model was obtained with Rcal2=0.97 and Rval2=0.91 for calibration and validation, respectively. This achievement suggested that the proposed NIR spectral acquisition using portable NIR spectrometer equipped with an integrating sphere is potential to establish an authentication system for ground roasted Indonesian specialty coffee in direct and fast measurement.