Selective Inhibition of Lipid Oxidation by a Quercetagetin-Rich Extract from Tagetes erecta: A Chemometric Approach Using OPLS-DA and Selectivity Index Analysis

This study investigates the antioxidant efficacy and selectivity of a quercetagetin-rich extract (QG, 89% purity) from Tagetes erecta in soybean oil under accelerated storage conditions (65 °C, 56 days). Using gas chromatography–mass spectrometry (GC-MS) fatty acid profiling, Headspace Solid-Phase Microextraction Gas Chromatography–Mass Spectrometry (HS-SPME-GC-MS) volatile analysis, and Orthogonal Partial Least Squares Discriminant Analysis (OPLS-DA) chemometrics, QG at 200 ppm was compared against a solvent control and propyl gallate (PG). QG preserved polyunsaturated fatty acids 5.2-fold more effectively than the control (p < 0.01), though it was less effective than PG in terms of overall Polyunsaturated Fatty Acid (PUFA) preservation. OPLS-DA-VIP analysis identified hexanal, hexanoic acid, and (E)-2-nonenal as preferentially suppressed volatiles (inhibition rates: 74.2%, 100%, and 81.2%, respectively), exceeding the average total volatile reduction (65.7%). A quantitative Selectivity Index (SI) combined with kinetic analysis supported preferential—rather than non-selective—inhibition of specific oxidation endpoints. Structure–activity relationship analysis suggested that the selectivity of the QG-rich extract may be associated with the catechol B-ring and unique 6-hydroxyl substitution of quercetagetin, its major component. The extract’s purity corresponds to a registered feed additive (Ministry of Agriculture and Rural Affairs (MOA) No. 618, 2022), ensuring industrial applicability. These findings establish the quercetagetin-rich extract as a promising selective natural antioxidant for PUFA-rich oils.