Optimization of extraction and enrichment of phenolics from pomegranate (Punica granatum L.) leaves

Pomegranate (Punica granatum L.) leaves, as byproducts, are rich sources of phenolic compounds and possess strong antioxidant activities. The aim of the present study is to optimize the extraction and enrichment conditions of phenolics from pomegranate leaves. Firstly, four solvents (water, 50% methanol, 50% ethanol and 50% acetone) were used to assess the effect of solvent polarity on the extraction yield and total phenolics content in extracts. Then, the response surface methodology based on three-level, three-variable Box–Behnken design was used to optimize and evaluate three independent variables: solvent concentration (25–50–75%), temperature (40–60–80 °C) and extraction time (20–40–60 min) on the extraction yield and total phenolics content. Thereafter, the macroporous resin chromatography was used to enrich the phenolics in the crude extract and the resin types, pH values of samples and elution solvent, and the concentration of elution solvent were optimized based on the absorption and desorption capacity of phenolics. Finally, the optimum conditions of extraction and enrichment were selected: the highest temperature (80 °C), the longest extraction time (60 min) and 61% ethanol solvent concentration for extraction; HPD-100 macroporous resin for chromatography, pH 2.0 for absorption sample solution, and 50% ethanol with pH 2.0 as desorption solvent. The extraction and enrichment process established here can be easily and effectively achieved, and the content of phenolics in the resulting extracts can reach 669.35 ± 19.50 mg GAE/g. Moreover, DPPH and ABTS radical scavenging abilities were significantly increased in the resulting extracts. This is the first time to study the enrichment of phenolics with macroporous resin chromatography from pomegranate leaves.

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► Extraction and enrichment conditions of phenolics were optimized.
► The optimum conditions for extraction were 80 °C, 60 min and 61% ethanol solvent.
► The optimum conditions for enrichment were HPD100 resin, pH 2.0, and 50% ethanol.
► DPPH radical scavenging abilities were significantly increased in the resulting extracts.
► Enriching phenolics with macroporous resin from pomegranate leaves for the first time.