Effect of Solvent Type, pH and Temperature on Polyphenol, Anthocyanin and Phytochemical Profiles of Pomegranate Peel Extracts Prepared by Maceration

Abstract

Pomegranate peel, an abundant agro-industrial by-product, was evaluated for its proximate composition and bioactive constituents, with emphasis on optimizing extraction conditions for phenolics, flavonoids, ascorbic acid, anthocyanins, and pectin. Proximate analysis (dry weight basis) showed that pomegranate peel powder contained 11.7 ± 0.11% moisture, 3.7 ± 0.05% crude protein, 2.1 ± 0.06% ether extract, 2.4 ± 0.08% ash, 15.3 ± 0.07% crude fiber, and 76.5 ± 0.16% available carbohydrates, highlighting its high fiber and carbohydrate content. Total phenolic content (TPC) was significantly affected by solvent type, extraction time, temperature, and pH. At 25 °C, the highest TPC was obtained after 24 h using 70% ethanol (321.30 ± 0.89 mg GAE/g) and 70% acetone (319.30 ± 1.24 mg GAE/g), whereas extraction at 5 °C markedly reduced TPC (maximum 188.11 ± 0.79 mg GAE/g). Acidic conditions enhanced phenolic recovery, with the highest TPC recorded at pH 2 using 70% acetone (332.80 ± 1.75 mg GAE/g). HPLC analysis identified 17 phenolic compounds, dominated by gallic acid (132.75 mg/100 g; 40.12%), chlorogenic acid (104.93 mg/100 g; 31.71%), and ellagic acid (32.80 mg/100 g; 9.91%). Total flavonoid content reached a maximum of 128.90 ± 1.48 mg QE/g at 25 °C using 70% acetone, while lower temperatures significantly reduced yields. Ascorbic acid ranged from 18.28 ± 1.34 to 33.45 ± 1.33 mg/g, with optimal extraction using 1–3% citric acid at 40–60 °C. Maximum anthocyanin content (30.62 ± 1.14 mg/100 g) was obtained with 3% citric acid after 120 min. Pectin yield increased with temperature and time, reaching 20.61 ± 0.20% at 90 °C for 90 min using 1% ammonium oxalate. These results demonstrate the strong potential of pomegranate peel as a functional food ingredient and a valuable source of natural bioactive compounds.