Rapid fruit extracts antioxidant capacity determination by Fourier transform infrared spectroscopy

The antioxidant content of fruits have made them a desirable component of the human diet. Several wet chemistry techniques, including the oxygen radical absorbance capacity (ORAC(FL)) assay, have been reported for measuring the antioxidant activities of fruit. In this study, we investigated the use of Fourier transform infrared spectroscopy (FTIR) to measure fruit antioxidant activity. Flavonoid-rich extracts from 5 blueberry, 5 grape, and 6 blackberry genotypes were obtained by methanol-water-formic acid (60:37:3, v/v/v) solvent. The total antioxidant capacities of the fruit extracts were determined by the ORAC(FL) assay, and the FTIR spectra of the fruit extracts were collected. Partial least squares (PLS) regressions with cross-validation was conducted on 128 spectra of extracts and their corresponding ORAC(FL) values to obtain a calibration model for predicting the antioxidant activity of the extracts. Spectra from an additional 16 extracts were used as an external validation set for the model. A good calibration model (R2 = 0.97) for antioxidant activity was obtained with satisfactory predictive ability (root mean standard error [RMSE] = 5.35) using the spectral region 2000/cm to 900/cm. Cross-validation procedures indicated good correlations (R2 = 0.94) between ORAC(FL) assay values and FTIR estimates. The ratio of the standard deviation of the data to the standard error of validation (RPD) values were above 5.0 for blueberry, grapes, and the combined extracts in the external validation set indicating that the calibration model was suitable for quantifying fruit extracts antioxidant activities. This study shows that an FTIR technique would be suitable for rapidly measuring fruit extract antioxidant activity.