Fourier Transform Infrared Spectroscopy for Antioxidant Capacity Determination in Colored Glutinous Rice

The determination of total phenolic content and antioxidant capacity of 48 colored rice varieties and two white rice varieties from Thailand by Fourier transform infrared (FT-IR) spectroscopy (400–4,000 cm−1) was performed to explore the possibility of using FT-IR as an effective alternative technique for such determination. The peak at 1,635 cm−1 resulted from the ring C-C stretch of phenyl was clearly observed. The levels of phenolic content in rice samples as indicated with infrared spectrum were consistent with the results from chemical assays. Dark glutinous rice had the highest level of antioxidant capacity and phytochemicals followed by red rice, brown rice, and white rice. The hierarchical cluster analysis based on selected principal components from principal component analysis model was performed to produce dendrograms which discriminated rice varieties according to their color well. The partial least squares regression models were constructed, and validated models were used to predict total antioxidant capacity and total phenolic content of the rice varieties. Satisfactory precision of prediction was achieved. With technical advantages that FT-IR offers especially when large number of samples are to be analyzed, FT-IR spectral features with chemometrics are suggested to be applicable for quantification and prediction of antioxidant capacity and phenolic compound content of colored rice.