A metabolomics approach based on 1H NMR fingerprinting and chemometrics for quality control and geographical discrimination of black pepper

Black pepper (Piper nigrum L.), known as the “king of spices”, is the most consumed spice and it is widely used as a food condiment due to its organoleptic properties. In this study, proton nuclear magnetic resonance (1H NMR) spectroscopy combined with chemometrics was employed for the first time for the discrimination of black pepper samples based on their geographical origin (Brazil, Vietnam, and Sri Lanka) and quality processing (sterilized or non-sterilized spice). 1H NMR fingerprints were obtained using a time-effective and simple ultrasound-assisted extraction method, and the performance of two complementary deuterated solvents was compared (chloroform and methanol). Principal component analysis (PCA) was utilized as an exploratory tool for cluster overview, whereas supervised orthogonal partial least squares discriminant analysis (OPLS-DA) was further applied for discrimination purposes. OPLS-DA models were characterized by high goodness-of-fit (R2 values between 0.962 and 0.971) and predictive ability for further black pepper samples (Q2 values in the range of 0.787−0.928). Piperine and other major metabolites were tentatively identified in black pepper and pointed out as chemicals markers that highly contributed to the sample clustering.