Abstract
In this investigation, Fourier transform-near infrared (FT-NIR) spectroscopy was used to determine the curcumin content in commercial turmeric herbal medicines. Two different sample presentations originating from a turmeric capsule and powder were evaluated and compared using an FT-NIR spectrometer equipped with a 30-capsule sample plate in the wavenumber region of 11,500–6000 cm−1 (transmittance mode) and a 6-vial sample plate in the wavenumber region of 10,000–4000cm−1 (reflectance mode), respectively. One hundred and forty samples of turmeric herbal medicines were divided into two sets: a training set with 110 samples and a prediction set with 30 samples. High-quality FT-NIR spectra for the turmeric powder containing the informative regions of curcumin (6850, 6000 and 4600 cm−1) were obtained while collecting FT-NIR data on the powder samples in the glass vials. A successful partial least-squares calibration model for curcumin content in commercial turmeric herbal medicine powders was then obtained by utilising the entire spectral region (10,000–4000 cm−1) as well as a second derivative spectral pretreatment containing seven principal components. The best model for predicting curcumin in 30 test samples returned a coefficient of determination (
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