Identification of phenolics responsible for the high antioxidant activity in Burdekin plum (Pleiogynium timoriense) fruit

Burdekin plum (Pleiogynium timoriense) is a widespread native edible fruit from Australia; however, there are limited studies exploring the chemical composition of this species. This study investigated the phytochemical composition of Burdekin plum flesh and seeds, finding a high antioxidant activity (12,571 mg Trolox equivalents/100 g as Ferric Reducing Antioxidant Potential), total phenolic content (10,928 mg gallic acid equivalents/100 g) and anthocyanin content (161 mg cyanidin-3-glucoside equivalents/100 g) in the flesh. The seeds also displayed a moderately high antioxidant activity (3,306 mg Trolox equivalents/100 g) and total phenolic content (2,344 mg gallic acid equivalents/100 g). Seventeen phenolic compounds were identified in the flesh and 14 in the seeds using targeted quantitative profiling using liquid chromatography - tandem mass spectrometry (LC-MS/MS). The most abundant compounds were cyanidin-3-glucoside and catechin in the flesh and seeds, respectively. Catechin also showed a high antioxidant activity, along with ellagic acid and gallic acid, while the activity of cyanidin-3-glucoside was relatively lower. Consequently, the main phenolic compounds contributing to the exceptionally high antioxidant activity of Burdekin plum flesh were identified as cyanidin-3-glucoside and ellagic acid. In the seeds, catechin provides a significant contribution to the antioxidant activity.