Simultaneous analysis of Curcumin and demethoxycurcumin in Curcuma xanthorriza using FTIR spectroscopy and chemometrics

Curcuma xanthorrhiza Roxb (Temulawak) contains curcuminoid with various pharmacological effects. To assure the quality and efficacy of C. xanthorrhiza, the content of curcuminoid in the product must be properly determined. This research aims to analyze the content of curcuminoid (curcumin and demethoxycurcumin) in ethanolic extract of C. xanthorrhiza using FTIR spectroscopy combined with partial least squares (PLS). The actual contents of curcuminoid in the ethanolic extract of C. xanthorrhiza were previously determined using HPLC with PDA detector. FTIR spectroscopy is validated by cross validation using leave-one-out (LOO) and external validation. The wavenumbers selected (4000-650 cm-1) were relied on its capability to provide the correlation between the actual value and the predictive value of curcuminoid, indicated by the highest R2 value with small PRESS and RMSEC values in the calibration model. During PLS calibration, the R2 values of calibration model and LOO for curcumin (C), demetoxycurcumin (DM) and total curcuminoid (TC) were > 0.99 with RMSEC, RMSECV and PRESS values were relatively small, whereas the R2 values for external validation were 0.98; 0.99; 0.98, with RMSEP and PRESS values were relatively small for C, DM and TC, respectively. Curcuminoid contents determined using FTIR spectroscopy combined with PLS were not statistically significant compared with HPLC method using independent sample t-test (P > 0.05). It can be concluded that FTIR spectroscopy combined with PLS can be used as an alternative method to determine the curcuminoid content in C. xanthorrhiza.