epicatechin-epicatechin or catechin-epicatechin types were also present in all five species, with A. pycnantha containing the highest number of procyanidin dimers. Myricetin derivatives, especially myricetrin, were also found in all four species but free myricetin aglycone was only identified after hydrolysis of the methanol extracts. Myricetin-galloyl-rhamnose was detected only in A. pycnantha methanol extract. The leaf extracts were analysed for total phenols (0.1 to 60.4 mg GAE/g DW, total odiphenols (0.1 to 22.3 mg CAE/g DW), total proanthocyanidins (0.1 to 36.9 mg CHE/g DW) and total flavonoids (2.4 to 153.2 mg QE/g DW). A. pycnantha methanol extract was the richest source of all phenolic compounds investigated. Bioscreening profiles were completed for antioxidant (DPPH, ABTS?+, FRAP, SOR, H2O2 scavenging assays), anti-diabetic (?-amylase and ?-glucosidase inhibition), neuroprotective (acetylcholine esteraseinhibition) and antimicrobial activities. All the methanol extracts gave consistently strong antioxidant activity for all methods. Again the A. pycnantha methanol extract was the outstanding performer in ABTS?+ (712.6 mM Trolox® equivalent (TE)g DW), DPPH (624.5 mM TE/g DW), SOR (EC50 value 0.08 mg/mL) but not for H2O2 (EC50 value 0.54 mg/mL) and FRAP (8.58 mM TE/g DW) which were lower than A. verniciflua dichloromethane extract. In case of anti-diabetic and neuroprotective activities, A. pycnantha methanol extracts exhibited the most potent a-amylase and acetylcholine enzyme inhibition assays, (IC50 0.004 mg/mL and 0.02 mg/mL respectively). However, no extracts showed anti-bacterial activity 24 (E. coli and S. aureus) except the A. implexa water extract which showed moderate activity against both Gram positive and Gram negative bacteria. Semi preparative HPLC fractionation (A, B and C) of the crude A. pycnantha methanol extract was performed.
|Qualification||Doctor of Philosophy|
|Award date||22 Mar 2016|
|Place of Publication||Australia|
|Publication status||Published - 2016|