Detection of Ochratoxin A in white wine at the legal limit via solvent-based enrichment and selective paper-enhanced infrared spectroscopy.

Abstract

Ochratoxin A (OTA) is a mycotoxin that occurs in many food products including cereals and wine, and is regulated at strict µg∙kg-1 levels. Spectroscopy-based methods have shown potential for mycotoxin detection but have limitations regarding selectivity, sensitivity and molecular identification. Here, we present a method that combines a 2-step pH-dependent liquid-liquid extraction with our recently developed selective paper-enhanced infrared spectroscopy (S-PEIRS), to empower label-free, selective and concentration-dependent detection of OTA contamination in wine at the legal limit. This combination allowed for the purification and enrichment of OTA, from white wine spiked at 2, 6 and 20 µg∙kg-1 into a focused area of a paper tip. A 2-step pH-dependent liquid-liquid extraction was optimized for OTA and benchmarked against high-performance liquid chromatography high-resolution mass spectrometry (HPLC-HRMS), showing extraction recoveries of ∼70% per extraction, and an average enrichment factor (EF) of 40. The extracts were further divided in 2 mL aliquots and applied to immunoaffinity columns (IACs) showing recoveries > 80%. Then, our approach leveraged the infrared detection of OTA on the paper tip, via the direct and linear detection of one of its molecular fingerprints (CO, 1660 cm-1). Overall, our approach represents the first demonstration of concentration-dependent detection of OTA contamination in white wine, with a detection limit at the legal limit of 2 µg∙kg-1, a limit of quantification of 6.7 µg∙kg-1 and strong correlation with independent HPLC-HRMS analysis (R2 = 0.963).