Identification of lipoxygenase inhibitors from litchi shell extract and their potential mechanism in delaying lipid oxidation and off-flavor formation in sunflower seeds.

Lipoxygenase (LOX) is considered a key target associated with lipid oxidation and quality deterioration of oil-seeds. In this study, high-affinity LOX inhibitors were screened from four plant extracts by UPLC-QTOF-MS, and their possible mechanism in delaying lipid oxidation and off-flavor formation of sunflower seeds was elucidated. Partial least squares-discriminant analysis (PLSDA) of LOX activity, electronic nose sensor response components, and oxidation indicator levels data showed that LOX activity was positively correlated with both lipid oxidation and off-flavor formation in sunflower seeds stored at 40 °C for 56 days. Three high-affinity LOX inhibitors, including epicatechin (EC, IC50 = 1.22 ± 0.07 mg/mL), epicatechin gallate (ECG, IC50 = 1.00 ± 0.03 mg/mL) and 6-gingerol (IC50 = 2.86 ± 0.11 mg/mL), were identified from litchi shell extract (LSE), which exhibited the strongest LOX inhibitory activity among 4 plant extracts. EC acted as a competitive inhibitor, whereas ECG and 6-gingerol functioned as mixed inhibitors. The results of multi-spectral analysis, AFM characterization and molecular docking confirmed each other, indicating that hydrogen bonding and hydrophobic interactions of inhibitors with residues of LOX drove the formation of inhibitor-LOX complexes, thereby inducing the changes of enzyme conformation and microenvironment, thus inhibiting the LOX activity, as well as the lipid oxidation and off-flavor of sunflower seeds. These findings propose a novel strategy for delaying lipid oxidation and off-flavor formation via targeted inhibition of LOX activity of oil-seeds and provide a theoretical basis for the application of LSE as a natural antioxidant in the preservation of lipid-rich food.