Antioxidant and anti-lipases activities in vitro of Mentha viridis and Eucalyptus globulus extracts

• Solvents affect bioactivity and phytochemical composition of plants extracts.
• Mentha and Eucalyptus extracts can be used as natural antioxidants in food.
• Mentha extract showed non competitive mixed inhibition mode against lipases.
• Eucalyptus extract showed competitive inhibition mode against lipases.
• Mentha and Eucalyptus extracts as new natural sources of lipase inhibitors.

Plants are a source of bioactive compounds such as antioxidants and enzyme inhibitors. In this work, effect of the Eucalyptus globulus and Mentha viridis extraction by different solvents on phenolics content, flavonoids content, condensed tannins content, antioxidant activity and inhibitory effect against two lipases from Aspergillus niger and olive was studied. Methanolic (MeOH) extract showed the strongest antioxidant and anti-lipase activities. High correlation between total phenolics content, total flavonoids content, antioxidant activity and lipases inhibitory action was observed. Kinetic analysis of lipases inhibition was performed with Linweaver-Burk, Dixon and Cornish-Bowden plots. These results revealed competitive inhibition mode by E. globulus and non competitive mixed inhibition mode by M. viridis against the two lipases. Inhibition constant (KI) values calculated with E. globulus MeOH extract were 0.271 and 0.188 mg/mL for Aspergillus niger and olive lipases respectively. With M. viridis MeOH extract KI values were 0.303 and 0.421 mg/mL for the fungal and the plant lipases respectively. The inhibitory concentration 50% (IC50) values determined with E. globulus MeOH extract were 0.69 mg/mL for Aspergillus niger lipase and 1.29 mg/mL for olive lipase. With M. viridis MeOH extract IC50 were 0.43 and 1.44 mg/mL for Aspergillus niger and olive lipases respectively.