Spice authentication: an AP-MALDI-MS approach to ground black pepper and oregano leaves

In recent years, the Joint Research Centre reported widespread fraud in the European market for six common herbs and spices, including oregano and black pepper. Fast and reliable analytical methods are crucial for verifying food authenticity and safeguarding consumers [1]. For this purpose, this study presents an innovative application of atmospheric pressure matrix-assisted laser desorption ionization mass spectrometry (AP-MALDI-MS) to detect adulteration in dried oregano leaves and ground black pepper, strengthening quality control efforts [2-4]. To this end, 44 oregano samples (23 authentic, 5 pure adulterants, and 16 adulterated) and 75 black pepper samples (37 typical, 5 pure adulterants, and 33 atypical) were analyzed directly in powder using an AP-MALDI source coupled to an ion trap mass analyzer, in both positive and negative ion modes. The most abundant ionic signals were characterized by multiple-stage MS/MS experiments and library searches, and the resulting spectral data were subjected to statistical analysis using multivariate statistical methods, including partial least squares discriminant analysis (PLS-DA). Random forest (RF) classifiers were then built to differentiate between authentic and adulterated samples. The RF classifier based on negative ion mode data for oregano showed the best performance, achieving 87.0% accuracy on the test set. For black pepper, the classifier using positive ion mode data performed better, with an overall test set accuracy of 85%. The study underscores the potential of AP-MALDI-MS as a rapid and cost-efficient screening method for establishing food authenticity, offering high sensitivity and specificity with minimal sample preparation requirements. This approach may serve as a valuable tool for regulatory agencies and food industry in addressing and preventing fraud within the spice trade. References 1. Nunes et al; Journal of Food Science, 83(4) (2018), pp 1036-1044. 2. Tata et al; Journal of Food Composition and Analysis, 109 (2022), pp 104-115. 3. Jones et al; Food Control, 120 (2021), pp 107-115. 4. Brown et al; Journal of Food Protection, 86(3) (2023), pp 450-463.