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Feijoa is a flowering plant in the Myrtle family. Its fruit, peel and leaf have been proved to be rich in aromatic volatiles, phenolic substances, minerals and dietary fibre, and they have various biological activities, like being anti-inflammatory, antibacterial, anticarcinogenic, and antioxidant (Basile et al., 2001; Vuotto et al., 2000). However, research on feijoa leaves is limited compared to that on feijoa fruits and peels. This project thus aims to study reliable extraction methods and characterise phenolic compounds in feijoa leaves and volatile compounds from the feijoa leaf essential oils. Water-steam distillation (WSD) and solvent extraction (SE) were investigated to optimise the extraction of essential oils and phenolic compounds, respectively, from two feijoa leaf cultivars, namely, Anatoki (AT) and Kakariki (KK), both of which are grown locally in New Zealand. The optimum conditions for essential oil extraction were: 600 g of sample loading and 6 hours of extraction time. The essential oil yield and the contents of volatile compounds of KK were considerably higher than those of AT. The primary volatile components were discovered as β-caryophyllene, germacrene D, β-pinene, longifolene-(V4), α-humulene and δ-cadinene by gas chromatography-mass spectrometry (GC-MS); these are all terpenoids. Besides, an orthogonal array design was used to optimise the extraction conditions for SE, which resulted in a 1:40 (w/v) solid-solvent ratio extracted for 20 mins at 50°C as optimal conditions. Results showed that the leaf from AT harboured a higher phenolic content than that of the KK cultivar. The key phenolic compounds in feijoa leaf extracts were characterised by liquid chromatography-mass spectrometry (LC-MS) and high-performance liquid chromatography (HPLC). Epicatechin, procyanidin B2 and catechin were found to be the dominant compounds. Moreover, procyanidin A2 and flavone were likely to exist in feijoa leaf extracts as per the results from liquid chromatography-electrospray ionization source-time of flight mass analyses (LC-ESI-TOF). The purification of the crude extracts from the feijoa leaf was conducted by precipitation and column chromatography. The Amberlite XAD-2 and Amberlite IRA-400 resins were compared for purification efficiency, using the same absorption and desorption (water, 60% ethanol & 60% acetone) programme. Results showed that the 60% ethanol fraction of the XAD-2 had a strong retention capacity, essentially for epicatechin (91.11%) and quercitrin (99.76%). Additionally, the 60% acetone fraction of the IRA-400 showed a good separation for hyperoside (80.97%). In summary, the results of the characterisation of the volatile compounds and phenolic compounds in the feijoa leaf suggested that the leaf could be used as a functional material in the food, pharmaceutical or cosmetic industries. Future in vitro and in vivo investigation in the bioactivity of feijoa leaf would be worth to be conducted. |
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