Effect of Microwave Roasting and Extraction Solvents on the Bioactive Properties of Coffee Beans

Identification of volatile compounds and antioxidant, antibacterial, and antifungal properties against drug-resistant microbes of essential oils from the leaves of Mentha rotundifolia var. apodysa Briq. (Lamiaceae)

The present research work investigated antioxidant, antibacterial, and antifungal properties of essential oils from the leaves of Mentha rotundifolia var. apodysa Briq. (EOR). Hydro-distillation was used to extract EOR before being subjected to the chemical characterization by the use of GC/MS. Antioxidant activity was assessed by the use of three bioassays namely 1,1-diphenyl-2-picrylhydrazyl (DPPH), ferric reducing antioxidant power (FRAP), and total antioxidant capacity (TAC). Antimicrobial potency was tested against gram-negative and gram-positive bacteria namely Staphylococcus aureus, Streptococcus pneumoniae, Escherichia coli, Acinetobacter baumannii, and Klebsiella pneumonia, while antifungal activity was tested against Aspergillus niger, Candida albicans, Aspergillus flavus, and Fusarium oxysporum. EOR yield was determined to be 1.31%, with 20 compounds wherein Menthol (31.28%) and Isomenthol (14.28%) constituted the greatest amount. Regarding antioxidant activity, EOR exhibited potent antioxidant power: DPPH (IC50 value of 0.36 ± 0.03 mg/mL), FRAP (EC50 value of 0.35 ± 0.03 mg/mL), and TAC (697.45 ± 1.07 mg EAA/g). Antibacterial activity results showed that EOR had broad antibacterial activity on the tested strains. Eventually, EOR resulted in the greatest inhibition zone diameters vs S. aureus (18.20 ± 0.41 mm) followed by E. coli (17.02 ± 0.5 mm). Antifungal activity results showed that EOR exhibited potent antifungal activity and resulted in the greatest inhibition zone diameters up to 51.32 ± 1.32 mm against Aspergillus flavus, and 34.51 ± 1.07 mm against Aspergillus niger.