In order to analyze the mechanism of the quality change of grass carp meat during cold storage, grass carp meat was stored at 4 ℃ and evaluated for changes in the composition of small-molecular-mass metabolites and ultrastructure after 24 and 72 h by gas chromatography time of flight-mass spectrometry (GC-TOF-MS) and transmission electron microscopy (TEM), respectively. As refrigeration time increased, the gap between muscle fibers became larger, the arrangement became disordered, and some sarcomeres were broken. A total of 211 metabolites were identified by metabolomics, of which 42 metabolites changed by more than 1.5 times (P < 0.05). The accumulation of lactic acid and phosphoric acid was the major reason for the pH decrease of fish meat. It was found that succinic acid was the only tricarboxylic acid (TCA) cycle metabolite that was significantly reduced (P < 0.05), which was converted into 4-hydroxybutanoic acid methyl ester and γ-aminobutyric acid, and levels of these three metabolites may be potential indicators of of the freshness of refrigerated grass carp meat. The contents of polyunsaturated fatty acids (such as linolenic acid and arachidonic acid) decreased significantly (P < 0.05), while the content of azelaic acid increased significantly (P < 0.05). Moreover, the contents of valine and L-cysteine increased significantly during cold storage (P < 0.05), and lipid oxidation preceded protein degradation. Plant secondary metabolites (piperine, naringenin, methyl jasmonate, loganin, α-ascarisin, abietic acid, and 3,4-dihydroxymandelic acid) contained in grass carp meat could affect the nucleotide metabolism and taste of fish meat by inhibiting xanthine oxidase.

To explore the anti-inflammatory mechanism of Camellia oleifera seed oil, the metabolites in ethanol extracts from 15 batches of C. oleifera seeds were analyzed by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and the inhibitory activity of the ethanol extracts on enteritis in Drosophila was evaluated by the “Smurf” test. The correlation between small molecular metabolites in the ethanol extracts and their anti-inflammatory activity was investigated and molecular docking with lipoxidase (LOX) was conducted to identify the key metabolites. Finally, the key metabolites were verified by the “Smurf” test. The results showed that the ethanol extract of C. oleifera seeds had good enteritis inhibitory activity, with percentage inhibition of 15.06%–61.71%, and its metabolites mainly included polyphenols, amino acids, organic acids, nucleotides, sugars and lipids. Seven polyphenolic compounds were identified in C. oleifera seeds for the first time. The monomeric compounds with good anti-enteritis activity were preliminarily identified as bruceine B, miltirone, 8-geranyloxypsoralen, cedrelone, wighteone, kaempferitrin and kaempferol-3-O-rutinoside. The anti-inflammatory activity of wighteone was reported for the first time in this study, and at 0.1 mg/mL, the percentage inhibition of enteritis was 64%, much greater than the positive control sulfasalazine (27.99%). This study lays the foundation for further exploring the anti-enteritis activity and mechanism of C. oleifera seed oil in vitro and in vivo.