Pittosporum angustifolium, known as gumbi gumbi, is a native Australian plant, which has traditionally been used as an Aboriginal medicine. This study investigates the effect of different solvents and extractive fermentation on the content and natural products composition of Pittosporum angustifolium extracts, and compares their antioxidant activity, in vitro α-amylase inhibition, and anti-inflammatory properties. Anti-inflammatory activity of the extracts was determined by measuring the inhibition of nitric oxide (NO) production. Extracts were characterised with FTIR-ATR spectroscopy, and screened for antioxidant activities and α-amylase inhibitory activity via High-performance thin-layer chromatography (HPTLC)-Effect-directed analysis (EDA) with direct bioautography. HPTLC combined with chemical derivatization and bioassays was used for EDA screening. The results show that lactic acid fermentation of gumbi gumbi leaves boosts the antioxidant activity in extracts by increasing the total phenolic content, but does not affect (increase or decrease) α-amylase inhibitory activity or nitrogen scavenging/anti-inflammatory activity. Analysis of the ATR-FTIR spectra from the band at RF = 0.85 that inhibits α-amylase, suggests that fatty acid esters are responsible for the enzyme inhibition; both saturated fatty acid esters in unfermented extracts and unsaturated fatty acid esters in fermented extracts. The ATR-FTIR spectra of the polyphenolics in fermented extracts (RF = 0.15-0.20) suggests the presence of soluble lignin fragments (i.e. lignins depolymerized into monomers and oligomers during the fermentation process).
Keywords: ATR-FTIR; Bioassays; Extractive fermentation; Gumbi gumbi; HPTLC; Lactic acid fermentation.
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