Determination of Total Phenolic Compounds and Antioxidant Activity of Ethanolic Extracts of Propolis Using ATR–FT-IR Spectroscopy and Chemometrics

Fourier transform mid-infrared spectroscopy equipped with attenuated total reflectance (FT-IR–ATR) combined to partial least squares (PLS) regression was used for the quantification of total phenolic contents (TPCs) and antioxidant activities in 98 samples of ethanolic extract of propolis (EEP) from the southwest region of Paraná, Brazil. The Pearson’s correlation coefficients were applied, and results ranged from 0.96 to 0.88 and showed higher correlation coefficients among TPC and ferric-reducing antioxidant power (FRAP) followed by 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) ABTS and 2,2-diphenyl-1-picrylhydrazyl hydrate (DPPH). Calibration was performed using a Savitzky-Golay filter (15 pt) and first derivative as well as standard normal variate (SNV) and mean center correction pretreatments. The determination coefficient in the calibration models ranged from 0.95 to 0.87. The range error ratio (RER) indicates the quality of estimation of the models and the results obtained were 10.0, 8.11, 16.8, and 8.99 for TPC, DPPH, ABTS, and FRAP, respectively. Thus, the results obtained for calibration and prediction parameters indicated that the models for DPPH, FRAP, and TPC have a low predictive capacity which complicates the data modeling. However, the ABTS model is validated and can be used for quantification of antioxidant activity of new extracts of propolis, being useful as an alternative to rapid analysis, reducing waste generation and cost, and indicating that the mid-infrared spectroscopy associated with PLS regression can be used to predict ABTS radical scavenger.