Subcritical water extraction of phenolic compounds from pomegranate (Punica granatum L.) seed residues and investigation into their antioxidant activities with HPLC–ABTS+ assay

Subcritical water extraction (SWE) of phenolic compounds from pomegranate seed residues (PSR) was performed. Total phenolic content (TPC) and antioxidant capacities of the extracts obtained at different temperatures were determined, and the individual antioxidant capacities were evaluated by coupling high performance liquid chromatography with ABTS radical reaction system (HPLC–ABTS+). The results showed that the optimum extraction time was 30 min, solid to water ratio was 1:40, and the highest TPC was obtained at 220 °C. The effect of extraction temperature on TPC was significant (p < 0.05), and TPC ranged from 651.7 to 4854.7 (mg/100 g DW) between 100 °C and 220 °C. HPLC–ABTS+ profiles revealed that nine compounds had antioxidant activity. Furthermore, the formation of Maillard reaction products during SWE was investigated, and the content of 5-hydroxymethylfurfural (5-HMF) was determined. The comparative study indicated that SWE was a promising technique for preparation of PSR phenolics.

► Subcritical water extraction of phenolics in pomegranate seed residue was proved to be effective.
► The HPLC-ABTS was an effective analytical technique for the separation of individual phenoilcs.
► Relation between Maillard reaction products and phenolics (by subcritical water) was conducted.