Polyphenol extraction and characterization of Justicia secunda Vahl leaves for traditional medicinal uses

•Justicia secunda leaves are used for traditional medicinal in tropical countries.•Mimicking traditional recipes, water-extracts were obtained at pilot plant scale.•The process included ultrasound-assisted extraction and membrane concentration.•Polyphenol content and antioxidant capacity were characterized during processing.•Structures of the two major extracted flavone-type compounds were determined.