Characteristics, Bioactives and Antioxidant Activity of Illawarra Plum (Podocarpus elatus) Fruit

Illawarra plums (IP) are native to Australia, having been used as bush food for centuries. This study characterized the physicochemical and antioxidant properties of mature IP and explored the efficacy of aqueous ethanol for extracting bioactives. The height, width, diameter, and weight of the fruit are 14.78 ± 3.1 mm, 17.45 ± 2.7 mm, 14.69 ± 3.0 mm, and 2.59 ± 1.2 g, respectively. The fruits were categorized into three ripening stages: unripe(green), almost-ripe(blushing), and ripe(red). The ripe fruit had a pH of 4.37 ± 0.03, total soluble solids of 9.3 ± 0.5°Brix, and a titratable acidity of 0.25 ± 0.01% w/v. The extraction solvents significantly influenced the yield of bioactives and antioxidant activity. The most effective solvent was 50% ethanol, which had total phenolics 123.93 ± 10.81 mg, flavonoids 130.58 ± 23.33 mg, proanthocyanins, and anthocyanins 16.12 ± 0.69 mg per gram of dried fruit. The extract exhibited potent DPPH radical scavenging properties (153.22 ± 39.67 mg TE/g). IP had five times more phenolics than African and American plums. Fourteen peaks were isolated by HPLC-PDA, with three tentatively identified as chlorogenic acid, epicatechin, and p-coumaric acid. IP shows great potential for the development of natural functional ingredients. Future research could explore individual phenolics and investigate the potential applications of IP in the food industry.