Application of FTIR spectroscopy and chemometrics for correlation of antioxidant activities, phenolics and flavonoid contents of Indonesian Curcuma xanthorrhiza

Curcuma xanthorrhiza is one of the most commonly used herbals found in Indonesian Traditional Medicine. This herb has been known as antioxidant. The phenolics and flavonoids are believed to be responsible for these activities. The objective of this study was to develop FTIR (Fourier transform infrared) spectra in conjunction with chemometrics of multivariate calibration for the prediction of antioxidant activity, total phenolics contents (TPC) and total flavonoid contents (TFC) of C. xanthorrhiza obtained from several locations in Indonesia. In this study, C. xanthorrhiza samples were subjected to antioxidant activity measurement based on DPPH radical scavenging assay and expressed by inhibition concentration of 50% (IC50), determination of TPC based on Folin-Ciocalteau reagent expressed as gallic acid equivalent (mg GAE/g) and determination of TFC based on its complexes with AlCl3 and expressed as quercetin equivalent (mg QE/g). The samples were also scanned using FTIR spectrophotometer at wavenumbers of 4000–650 cm−1 based on attenuated total reflectance (ATR) measurement. The antioxidant activities, TPC and TFC were correlated with FTIR spectra with the aid of multivariate calibration. The results showed that IC50 values of C. xanthorrhiza powder were within 0.177–0.615 mg/mL, TPC of 0.438–1.214 mg GAE/g and TFC of 0.058–0.229 mg QE/g. PLS regression for the correlation between actual values of IC50 and FTIR predicted values were of 0.9919 indicating the high accurate prediction method. From ANOVA test, the error obtained is low, i.e., 0.0027 indicating the precise method. The similar results in terms of high accuracy and precision were also obtained during the employing FTIR spectra and PLS for prediction of TPC and TFC. It can be concluded that the combination of FTIR spectroscopy and chemometrics can provide the alternative methods for prediction of antioxidant activities using DPPH radical assay, TPC and TFC with the main advantage of simple in operation and minimum use of solvents.