Rapid detection of pork oil adulteration in snakehead fish oil using FTIR-ATR spectroscopy and chemometrics for halal authentication

The current study aimed to develop an authentication technique using FTIR (Fourier transform infrared) spectroscopy and chemometrics to detect pork oil (PO) adulteration in snakehead fish oil (SFO). Twenty-one series of adulterated SFO samples were prepared by mixing SFO and PO in binary mixtures with several concentration level of PO ranging from 0 to 100% v/v. FTIR spectra of SFO and PO were very similar but SFO has a unique peak at 1418 cm−1, which is only observed in a very little shoulder in PO. The FTIR spectra were mainly from the vibration of functional groups from fatty acids and triacylglycerols. Chemometrics of principal component analysis (PCA) using 12 principal components successfully differentiated authentic and adulterated SFO samples. Classification of authentic SFO and adulterated SFO with PO was successfully obtained using orthogonal projections to latent structures–discriminant analysis (OPLS-DA) with good of fitness (R2X = 0.986; R2Y = 0.818) and good of predictivity (Q2 = 0.620). The vibrations of 1743 cm−1, 1720 cm−1, 1712 cm−1, and 1708 cm−1 (carbonyl groups); variables of 1161 cm−1, 1153 cm−1, 1137 cm−1, and 914 cm−1 (bending vibration of –CH3, –CH2, and –CH groups), and variables of 1107 cm−1 and 1099 cm−1 (C–O vibration) were found as differentiating wavenumber for samples differentiation. Permutation test and receiver operating characteristics (ROC) analysis confirmed the validity of the OPLS-DA model. The concentration of PO in SFO was successfully predicted using partial least square (PLS) and orthogonal PLS (OPLS) with high accuracy (R2 > 0.990) and high precision (RMSEE and RMSECV < 5.00) in both models. From the S-line plot, variables of 1708 cm−1, 1153 cm−1, 1107 cm−1, and 914 cm−1 had important roles in creating OPLS model. It can be concluded that a combination of FTIR spectroscopy and chemometrics could be used to as a rapid analytical method for halal authentication of SFO.