Determination of the iodine value and the free fatty acid content of waste animal fat blends using FT-NIR

•FTNIR spectra and pre-processing of animal fat wastes.•Rapid determination of iodine value and free fatty acids by FTNIR.•Simultaneous determination of quality parameters for animal fat blends.•Excellent correlation between the calculated values and PLS models.

This study determined iodine value (IV) and free fatty acids (FFA) content of four different animal fat wastes and their blends using Fourier transform near-infrared spectroscopy (FT-NIR). Chemometric analysis by partial least squares (PLS) regression was used to correlate spectral data with IV and FFA reference values of the samples. The effects of four spectra pre-processing (first derivative (FD), second derivative (SD), multiplicative scatter correction (MSC) and vector normalization (VN)) methods were investigated to predict the reproducibility and robustness of the PLS-NIR model developed. A set of 70% of animal fat wastes and their blends were used for developing PLS calibration models for measuring IV and FFA content using the remaining 30% samples as an independent test set validation. The coefficient of determination (R2), the root mean square error estimation (RMSEE), and the residual prediction deviation (RPD) were used as indicators for the predictability of the PLS models. PLS-NIR models developed using first derivative and second derivative spectral preprocessing methods were the best for both IV and FFA content analysis (For IV, FD; R2 = 0.9870, RMSEE = 1.40 gI2/100 g, RPD = 8.76, SD; R2 = 0.9892, RMSEE = 1.28 gI2/100 g, RPD = 9.64 while For FFA, FD; R2 = 0.9991, RMSEE = 0.195%, RPD = 34.00, SD; R2 = 0.9993, RMSEE = 0.182%, RPD = 36.8). Overall, the results of this study demonstrate the suitability of FT-NIR spectroscopy for the quality control analysis of feedstocks for biodiesel production.