Curcuminoid, the main components in Curcuma species, is responsible for several biological activities including antioxidant and hepatoprotective effect, therefore fast and reliable analytical method is required for curcuminoid assay. The objective of this study was to develop Fourier transform infrared (FTIR) spectroscopy in combination with multivariate calibration of partial least square (PLS) and princple component regression (PCR) for quantitative analysis of curcumin (CUR) and demethoxycurcumin (DMC) in syrup sample containing extract of Curcuma xanthorriza (temulawak). Syrup samples were directly scanned using FTIR spectrophotometer with attenuated total reflectance (ATR) sampling technique at wavenumbers 4000-650 cm-1 and its spectra were correlated with contents of CUR and DMC determined using high performance liquid chromatography. PLS offered better prediction model for the relationship between actual values of CUR and DMC and FTIR predicted values using absorbances at wavenumbers of 3004-974 cm-1 than PCR. PLS calibration model yield R2 of 0.9999 (calibration) and 0.9976 (for validation). The errors in calibration and validation expressed by root mean square error of calibration (RMSEC) and root mean square error of calibration (RMSEC) and root mean square error of prediction (RMSEP) were low, i.e. 0.0014 (RMSEC) and 0.0017 (RMSEP), respectively. FTIR spectroscopy in combination with PLS provide fast, accurate and precise method for determination of CUR and DMC in syrup samples.
Key words: FTIR spectroscopy, curcumin, demethoxycurcumin, partial least square, syrup.
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