Temperature‐dependent extraction and chromatographic recovery and characterisation of ellagitannins with potent antioxidant and glycaemic control properties from ‘Wonderful’ pomegranate peel

Abstract

SummaryPomegranate peel contains bioactive ellagitannins including punicalagin, a major bioactive principle. However, studies have not optimally recovered and evaluated these ellagitannins for their antioxidant and glycaemic control potential. In the present study, a temperature‐dependent extraction was employed to optimally recover bioactive ellagitannins and punicalagin from pomegranate (variety ‘Wonderful’) peel. The peel was extracted with distilled water at different temperatures (25, 37, 50, 65, 78 and 95 °C) and evaluated for phenol and flavonoid contents, in vitro antioxidant and enzyme inhibitory activities. XAD16N resin was used to recover tannins from the extracts and punicalagin was purified from the tannin recovered from the 78 °C crude extract. LC–MS was used to characterise the ellagitannins profile. The dose‐dependent anti‐lipid peroxidative and glucose uptake potential of the punicalagin and its parent crude extract and tannin were measured. The extract obtained at 78 °C had the highest phenolic, flavonoid, tannin and punicalagin contents, which potentiated stronger radical scavenging, ORAC (IC50 = 9.64 vs. 15.6 and 25.6 μg/mL, respectively), anti‐linoleic acid peroxidative (IC50 = 9.97 vs. 19.9 and 27.3 μg/mL, respectively) and antiglycation (IC50 = 29.1 vs. 34.2 and 79.1 μg/mL, respectively) activities than the extract and the purified punicalagin. Similarly, the cellular anti‐lipid peroxidative and glucose modulatory effects of the recovered tannin (IC50 = 3.67 μg/mL; EC50 = 14.8 μg/mL) better than that of the extract (IC50 = 24.3 μg/mL; EC50 = 55.0 μg/mL) and the purified punicalagin (IC50 = 59.0 μg/mL; EC50 = 112 μg/mL), which may be attributed to the complementary action of the tannin's constituent compounds (punicalagin, ellagic acid, granatin A, corilagin, casuarinin, gallic acid and quercetin hexoside). The α‐amylase inhibitory data, however, suggest the purified punicalagin influences enzyme inhibitory potential of pomegranate peel. The study suggests tannin/ellagitannin purified from pomegranate peel aqueous extract obtained at 78 °C may be a promising dietary supplement for exerting glycaemic control and mitigating oxidative stress.