A large variety of unique and distinct flora of Australia have developed exceptional survival methods and phytochemicals and hence may provide a significant avenue for new drug discovery. This study proposes a bioassay guided fractionation protocol that maybe robust and efficient in screening plants with potential bioactive properties and isolating lead novel compounds. Hence, five native Australian plants were selected for this screening process, namely Pittosporum angustifolium (Gumbi gumbi), Terminalia ferdinandiana (Kakadu plum, seeds (KPS), and flesh (KPF)), Cupaniopsis anacardioides (Tuckeroo, seeds (TKS) and flesh (TKF)), Podocarpus elatus (Illawarra plum, seeds (IPS) and flesh (IPF)) and Pleiogynium timoriense (Burdekin plum, seeds (BPS) and flesh (BPF)). The methanolic extracts of the plants samples were analysed for Total phenolic content (TPC) and antioxidant capacity measure by FRAP. The highest values were found in the KPF which were 12,442 ± 1355 mg GAE/ 100 g TPC and 16,670 ± 2275 mg TXE/100 g antioxidant capacity. Extracts of GGL was deemed to be most potent with complete cell inhibition in HeLa and HT29, and about 95% inhibition in HuH7 cells. Comparative activity was also seen for KPS extract, where more than 80% cell inhibition occurred in all tested cell lines. Dose-dependent studies showed higher SI values (0.72–1.02) in KPS extracts than GGL (0.5–0.73). Microbial assays of the crude extracts were also performed against five bacterial strains commonly associated with causing food poisoning diseases were selected (Gram positive—Staphylococcus aureus and Gram negative—Escherichia coli, Salmonella typhi and Pseudomonas aeruginosa bacteria). KPF extracts were effective in suppressing microbial growth of all tested bacterial strains except for P. aeruginosa, while TKS and TKF were only slightly effective against S. aureus. Due to the potential of the GGL crude extract to completely inhibit the cells compared to KPS, it was further fractionated and tested against the cell lines. HPLC phenolic profiling of the crude extracts were performed, and numerous peak overlaps were evident in the fruit extracts. The KPF extracts demonstrated the strongest peaks which was coherent with the fact that it had the highest TPC and antioxidant capacity values. A high occurrence of t-ferulic acid in the GGL extracts was found which may explain the cytotoxic activity of GGL extracts. Peaks in KPS and KPF extracts were tentatively identified as gallic acid, protocatechuic acid, 4-hydroxybenzoic acid and syringic acid and possibly ellagic acid. HPLC time-based fractionation of the GGL extract (F1–F5) was performed and Dose dependent cytotoxic effects were determined. It was construed that F1, having the highest SI value for HeLa, HT29 and HuH7 (1.60, 1.41 and 1.67, respectively) would be promising for further fractionation and isolation process.

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The Central Queensland region of Australia is a large producer of horticultural produce; however, there are limited studies on the phytochemical composition of the produce from this region. Additionally, some crops or cultivars are poorly known in domestic markets; hence are currently only grown for niche markets. There is opportunity to expand production of these crops if they contain higher levels of health-benefiting compounds compared to existing cultivars. Hence this work aimed to elucidate the phytochemical composition of such under-marketed and/or under-utilised crops, including their phenolic acid and flavonoid profiles. The samples included nine cucurbits, two citrus fruits, dragonfruit and Brazilian cherry. The vitamin C (ascorbic acid) content was quantified using high-performance liquid chromatography with diode array detection, while the phenolic profiles were gathered using targeted liquid chromatograph tandem mass spectrometry analysis. Antioxidant activity was quantified using the FRAP and CUPRAC assays, while total phenolic content was measured using the Folin-Ciocalteu assay. The results revealed extensive variation in the levels of health-benefiting compounds between the samples. The phenolic profiles of several species/cultivars are reported for the first time. The highest ascorbic acid content was found in blood orange skin (817 mg/100 g DW), while the highest total phenolic content was found in blood orange skin (1988 mg GAE/100 g). Samples showing high antioxidant capacity included blood orange skin, Brazilian cherry and spaghetti squash. These results may support the prospect of marketing several of the crops/cultivars as functional food crops in domestic or export markets.