Assessing the authenticity of black pepper using diffuse reflectance mid-infrared Fourier transform spectroscopy coupled with chemometrics

Diffuse reflectance mid-infrared Fourier transform spectroscopy (DRIFTS) coupled with chemometrics was used to examine the possibility of verifying the origin and authenticity of black pepper in this study. DRIFTS were obtained for 150 pure black pepper samples of different geographical origin (Kerala, HaiNan, DongNai, Sarawak, Fujian) and 1200 fake black pepper (adulterated with sorghum or Sichuan pepper, doping levels from 5% to 50%, respectively) by recording within a spectroscopic range of 4000–400 cm−1. Collected data were treated using principal component analysis (PCA), genetic algorithm optimized support vector machine (GA-SVM) and partial least squares discriminant analysis (PLS-DA). PCA model of the DRIFTS revealed the clustering trend of the pure and fake black pepper samples. Accurate and reliable classification results were obtained by DRIFTS combined GA-SVM and PLS-DA model. For the pure black pepper sample, the training set and prediction set of GA-SVM and PLS-DA models all achieved 100% correct recognition rate. For the fake black pepper sample, the total recognition rate of GA-SVM and PLS-DA model were greater than 98% for the training sets and more than 96% for the predicted sets, respectively. The results of this study demonstrated that DRIFTS method combined with chemometric tools can be successfully applied to detect mislabeling and adulteration of black pepper.