Evaluation of different post-harvest treatments on Malaysian mistletoe (Scurrula ferruginea (Jack) Dans.) leaves extracts yield, antioxidant and antimicrobial performance

Scurrula ferruginea is hemiparasitic mistletoes from the family Loranthaceae that widely distributed in tropical regions and has been used traditionally as medicinal plants in Southeast Asian countries. In earliest studies, the plant is known to have antioxidant and antimicrobial activities. However, the best drying methods towards the preservation of phenolic compounds of the plant as well as a suitable solvent for extracting the antioxidants and antimicrobial activity have not been optimized. In this study, the determination of the best drying methods (air and oven) and extraction solvents (aqueous, organic and aqueous organic) on phenolic compounds, antioxidant and antimicrobial activity were carried out. Total Phenolic Content (TPC) and Total Flavonoid Content (TFC) were used to determine the phenolic compound, while antioxidant activity was evaluated by measuring the scavenging effect on 2,2- diphenyl-1-picrylhydrazyl (DPPH) radical and Ferric Reducing Antioxidant Power (FRAP). Antimicrobial activity of the extracts was tested against 2 pathogenic bacteria (Staphylococcus aureus S261 and Escherichia coli E57) and 2 pathogenic fungi species (Candida albicans C205 and Trichophyton rubrum T62) using Disc Diffusion Method, Minimum Inhibitory Concentration (MIC), Minimum Bactericidal Concentration (MBC) and Minimum Fungicidal Concentration (MFC) respectively. The optimal conditions for S. ferruginea were oven drying, using 80% methanol solvent with values of 2.72 mg/10g DW (extract yield), 168.18 mg GAE/1g DW (TPC), 25.03 mg QE/1g DW (TFC), 27.86 mg TE/1g DW (FRAP), 94.0% (DPPH) and 19.32 μg/mL (IC50). The result of this research shows a potent antioxidant activity in S. ferruginea leaves extracts as compared to standard antioxidants (Ascorbic acid and Trolox). A correlation study of the extracts revealed significant positive correlations (P < 0.05) between extraction yields, phenolic compounds and antioxidant properties. The extracts exhibited optimum antimicrobial activities on both Staphylococcus aureus S261 and Escherichia coli E57 with a zone of inhibition ranging from 7.98 to 9.71 mm and 450 to 900 μg/mL (MIC and MBC). However, the extracts show no inhibitory effects on C. albicans C205 and T. rubrum T62. Present results suggested that post-harvest preparations such as drying method (oven drying) and extractions solvents (80% methanol) variability play a crucial role in enhancing the efficiency and efficacy of plant samples. The findings obtained in this study shows that S. ferruginea leaves are highly potential source of antioxidant and antimicrobial discovery that leads for new nutraceutical