Volatile compounds from the peel of the Australian finger lime (Citrus australasica): Identification and in silico bioactive potential

The Australian finger lime (Citrus australasica F.Muell.) is one of six Citrus species endemic to Australia, being found in the subtropical rainforest region around the Queensland and New South Wales border. The fruit is filled with characteristic ovoid or spherical pulp vesicles, giving the pulp a caviar-like appearance. Finger lime has recently been exploited in boutique restaurants due to its unique organoleptic profile, with interest also shown by pharmaceutical and cosmetic industries. However, there is limited information on the chemical composition of this species, including the volatile constituents of commercially available cultivars. We used gas chromatography coupled with single quadrupole mass spectrometry (GC-MS) to investigate the volatile organic constituents in the peel extracts from five commercial finger lime cultivars.1 Compounds were identified from their mass spectra and linear retention indices. The in silico bioactivity of the identified compounds was predicted using the Molinspiration web tool (https://www.molinspiration.com/). The majority of volatile compounds were predicted to have no to moderate activity against a range of receptor types (GPCR ligand, ion channel modulator, kinase inhibitor, nuclear receptor ligand, protease inhibitor, enzyme inhibitor). However, several compounds – namely shyobunol, δ-elemene and (1R,7S,E)-7-isopropyl-4,10-dimethylenecyclodec-5-enol – showed potential for acting as nuclear receptor ligands. Other studies have reported anti-inflammatory, antimicrobial and anti-tumour activity of some of the other volatile compounds identified, including limonene, β-myrcene, citronellal and α-pinene.2-4 This recommends further investigation into the bioactive potential of compounds from C. australasica, using more sophisticated in silico and in vitro approaches.