Effect of blanching pretreatment on the phytochemical properties, and bioactivities of Herskawitz pomegranate peel extracts at three different harvest maturities
Herskawitz (Punica granatum L.) is the pomegranate cultivar with the second largest distribution in South Africa (9%). The cultivar is one of the largest contributors of fruit waste (seed and peel) at approximately 703,000 t in packhouses in 2020. The fruit peel is known for its high phytochemical content and strong biological activity. Yet, it is often discarded in landfills creating an environmental problem or utilized as animal feed when it could be turned from waste to wealth by creating value-added products. The first step in achieving this is investigating novel ways of preserving and extracting high phytochemical content that is inexpensive, simple, and easy to set up. In this study, blanching at 80°C for 3 min has been shown as a novel pretreatment step to preserve the integrity of the phytochemical content within the peel extracts by lowering enzyme activities (i.e., polyphenol oxidase (PPO) and peroxidase (POD)) that negatively affect phytochemical content. This study aimed to investigate the effect of blanching pretreatment on the phenolic content, antioxidant properties, enzyme inactivation, and antibacterial activity of Herskawitz peel extracts at three different harvest times (unripe, ripe, and overripe). Moreover, the effect of blanched peel extracts against Klebsiella pneumonia, Escherichia coli, Staphylococcus aureus and Bacillus subtilis bacteria was assessed. All blanched peel extracts reduced PPO and POD activities and higher phytochemical, antioxidant and antibacterial activities compared to unblanched peel extracts, regardless of harvest maturity. However, ripe blanched Herskawitz peel extracts had significantly lower PPO and POD activity at 0.25 and 2.79 U g‑1 FW, respectively, and the highest extract yield (26.96% DM), total phenolic content (16.24 mg GAE g‑1 DM), total tannin content (2.18 mg GAE g‑1 DM), total flavonoid content (1.95 CE g‑1 DM), 2,2-diphenyl-1-picryl hydrazyl antioxidant activity (637.55 µmol Trolox g‑1 DM), and ferric ion reducing antioxidant power (817.43 µmol Trolox g‑1 DM). The lowest minimum inhibitory concentration value of 80 µg mL‑1 for B. subtilis and K. pneumonia bacteria strains was reported for ripe blanched Herskawitz peel extracts. This study validates the possible commercial utilization of blanched Herskawitz pomegranate peel extracts at different harvesting times, especially those from the ripe harvest maturity stage, to either fortify old or new value-added products or create new products in the pharmacological, cosmeceutical and nutraceutical industries.
Magangana, T.P., Makunga, N.P., Fawole, O.A. and Opara, U.L. (2022). Effect of blanching pretreatment on the phytochemical properties, and bioactivities of Herskawitz pomegranate peel extracts at three different harvest maturities. Acta Hortic. 1349, 619-628
antioxidant activity, antibacterial activity, harvest maturity, hot water blanching, phytochemical content, pretreatment, processing, value-addition