Mild extrusion enhances bioactive retention and starch digestibility in pigmented corn: Phenotype-dependent effects for functional food development

This study reveals the unexpectedly significant impact of very mild extrusion (50 °C, 30 % moisture) on bioactive compounds and starch digestibility in pigmented corn flours (yellow, orange, red, purple), demonstrating that even low-temperature processing can profoundly alter functionality. Despite the gentle conditions, extrusion induced colour-dependent shifts: yellow corn showed a 19 % increase in total phenolic content (TPC), while orange and purple corn declined (9 % and 8 %, respectively). Red corn emerged as the most stable, retaining the highest DPPH activity (exceeding other phenotypes by 6–56 %) and ferric reducing power (+49 % in orange corn). Strikingly, starch digestibility diverged dramatically—RDS (rapid-digestible starch) surged by 81 % in red corn but decreased by 20 % in purple corn, while resistant starch (RS) dropped universally (56–81 %). FTIR confirmed structural reorganization of starch-phenolic complexes, and e-nose data revealed superior volatile retention in red/purple corn. These findings challenge assumptions about thermal vulnerability, positioning mild extrusion as a strategic tool for tailoring functional ingredients specifically for pigmented corn matrices, where phenotype-dependent responses enable selective enhancement of bioactive retention (red corn) or digestibility modification (purple corn) depending on intended applications. • Mild extrusion modulated antioxidant profiles in pigmented corn flours. • Red corn retained the highest DPPH and FRAP antioxidant activity post-extrusion. • Extrusion increased rapidly digestible starch, especially in red and orange corn. • Purple corn uniquely showed reduced starch digestibility after extrusion. • Volatile profile and anthocyanin stability were preserved in red and purple corn.