Extrusion-cooking of plant materials may enhance antioxidant activity and improve health benefits. Selected antioxidant polyphenols in extruded corn gruels enriched with different amounts of linden flowers were determined by LC-ESI-MS/MS and quality characteristics were determined. Phenolic content increased with Tiliae inflorescentia addition and was not decreased by high-temperature extrusion. Linden flower incorporation into instant gruels should be limited to 10% to retain acceptable sensory properties.