Bitter orange, Citrus aurantium L. var. amara (CAVA), is an important crop and its flowers and fruits are widely used in China as a food spice, as well as in traditional Chinese medicine, due to its health-promoting properties. The secondary metabolites that are present in plant-derived foods or medicines are, in part, responsible for the health benefits and desirable flavor profiles. Nevertheless, detailed information about the bioactive ingredients in CAVA is scarce. Therefore, this study was aimed at exploring the phytochemicals of CAVA by high performance liquid chromatography/quadrupole time-of-flight mass spectrometry (HPLC-Q-TOF-MS). Here, a systematic screening method combined with HPLC-Q-TOF-MS was presented. This technique was used to systematically screen metabolites, primarily from the complex matrix of CAVA, and to identify these compounds by their exact masses, characteristic fragment ions, and fragmentation behaviors. A total of 295 metabolites were screened by the screening method and 89 phytochemicals were identified in the flowers, fruits, roots, leaves, and branches of CAVA. For the first time, 69 phytochemicals (flavonoids, alkaloids, terpenoids, etc.) were reported from CAVA. The results highlight the importance of CAVA as a source of secondary metabolites in the food, medicine, and nutraceutical industries.

In recent years, synthetic antioxidants that are widely used in foods have been shown to cause detrimental health effects, and there has been growing interest in antioxidants realised from natural plant extracts. In this study, we investigate the potential effects of natural antioxidant components extracted from the forage plant marigold on the oxidative stability of soybean oil. First, HPLC-Q-TOF-MS/MS was used with 1,1-diphenyl-2-picrylhydrazyl (DPPH) to screen and identify potential antioxidant components in marigold. Four main antioxidant components were identified, including quercetagetin-7-O-glucoside (1), quercetagetin (2), quercetin (3) and patuletin (4). Among them, quercetagetin (QG) exhibited the highest content and the strongest DPPH radical scavenging activity and effectively inhibited the production of oxidation products in soybean oil during accelerated oxidation, as indicated by reductions in the peroxide value (PV) and acid value (AV). Then, the fatty acids and volatile compounds of soybean oil were determined with gas chromatography–mass spectrometry (GC-MS) and headspace solid-phase microextraction–gas chromatography–mass spectrometry (HS-SPME-GC-MS). A total of 108 volatile components, including 16 alcohols, 23 aldehydes, 25 ketones, 4 acids, 15 esters, 18 hydrocarbons, and 7 other compounds, were identified. QG significantly reduced the content and number of aldehydes and ketones, whereas the formation of acids and hydrocarbons was completely prevented. In addition, the fatty acid analysis demonstrated that QG significantly inhibited oxidation of unsaturated fatty acids. Consequently, QG was identified as a potential, new natural antioxidant that is believed to be safe, effective and economical, and it may have potential for use in plant extracts feed additives.

Quercetagetin (QG), a principal flavonol from marigold (Tagetes erecta L.), is recognized for its potent antioxidant properties. However, its efficacy in mitigating intestinal injury under heat stress (HS) conditions remains unclear. We investigated the protective effects of QG using a mouse model of HS (41 °C, 70% humidity). Mice received oral QG (100 mg/kg/day) or saline for seven consecutive days before and during HS exposure. We assessed jejunal histopathology, oxidative stress markers, inflammatory cytokines, gene expression, and gut microbiota composition via 16S rRNA sequencing. QG supplementation significantly ameliorated HS-induced jejunal damage. It enhanced the activities of superoxide dismutase (SOD) and catalase (CAT) while reducing malondialdehyde (MDA) and pro-inflammatory cytokines (IL-1β, IL-6, TNF-α). QG downregulated the mRNA expression of heat shock proteins (Hsp70, Hsp90) and upregulated antioxidant-related genes (SOD1, GPX4, CAT, NQO1, Nrf2). Furthermore, QG preserved intestinal barrier integrity by upregulating tight junction proteins (Occludin, Zo-1, Claudin). 16S rRNA analysis revealed that QG significantly reshaped the gut microbiota, marked by an increased relative abundance of Lactobacillus and a decrease in potentially harmful taxa such as Allobaculum, Oscillibacter, and Colidextribacter. QG effectively alleviates HS-induced intestinal injury by enhancing antioxidant capacity, suppressing inflammation, and modulating the gut microbiota. These findings provide a scientific basis for the potential application of QG as a functional feed additive to improve animal health under heat stress conditions.

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.