Potential of phenolic compounds in Ligustrum robustum (Rxob.) Blume as antioxidant and lipase inhibitors: Multi‐spectroscopic methods and molecular docking

Ligustrum robustum (Rxob.) Blume is traditionally served as a functional tea in China. In this work, the antioxidant activities of L. robustum (Rxob.) Blume extract (LRE) were evaluated and its inhibitory effect and mechanism on pancreatic lipase were further investigated. With the high contents of phenols (139.70 ± 1.41 mg gallic acid equivalent/g extract) and flavonoids (326.46 ± 7.36 mg rutin equivalent/g extract), LRE showed significant antioxidant activities (p < 0.05) for scavenging free radicals and hydrogen peroxide, inhibiting lipid peroxidation and providing strong reducing power. Meanwhile, LRE displayed remarkable inhibitory activity on pancreatic lipase with a low half-effective inhibitory concentration (IC50 ) of 2.469 ± 0.005 mg/ml which was further determined as non-competitive inhibition. The spectroscopic results showed that LRE inhibited the activity of pancreatic lipase by modifying the tertiary and secondary structures of lipase. Moreover, four phenolic compounds (acteoside, lipedoside A, oleuropein and ligurobustoside C) were identified from LRE by the high performance liquid chromatography-quadrupole- time of flight-mass spectrometry. In addition, according to molecular docking analysis, the four phenols could interact with pancreatic lipase by hydrogen bonds, so as to change the spatial structure of pancreatic lipase and inhibit its catalytic activity. The present results suggest that LRE not only exhibits strong antioxidant capacity but possesses effectively inhibitory activity on pancreatic lipase, which might have the potential to be developed as functional food and nutraceuticals for the prevention of metabolic diseases. PRACTICAL APPLICATION: Ligustrum robustum (Rxob.) Blume extract has been confirmed to possess antioxidant activity and lipase inhibitory activity, which indicates that the L. robustum extract has the potential to prevent oxidative stress and regulate fat metabolism. This work suggests that L. robustum extract can be served as a novel resource to prepare nutraceuticals and functional food in food industries.