Enhancement of retrograded maize amylopectin in aged starch paste by screening Monascus strains under solid fermentation

Retrograded starch (type 3 resistant starch), known for its laxative properties, has garnered significant research interest. Nevertheless, the inherently low levels of retrograded starch in aged starch paste restrict its practical applications. Monascus strains named as M1, M2, M3, M4, and M5 were isolated from various red mold rice produced in China and were employed to enhance contents of retrograded maize amylopectin in aged starch paste. The results demonstrated that optimal addition of aged starch and coxi seed was observed at a 1:1 ratio in a solid medium. The highest content of retrograded maize amylopectin in aged starch was achieved after 15 days of fermentation by strain M2 at 32 ℃, increasing from 39.5% to 73.1%, which represents an 85.1% enhancement. The results of FT-IR, 13C solid-state NMR, XRD and DSC revealed that the ω-gliadin at β-sheet and β-turn state served as a valuable nitrogen source for Monascus M2 growth. The maize amylopectin in the amorphous region were decomposed by Monascus . The crystals for retrograded maize amylopectin were characterized by diffraction angles at 2θ 19.1°. This study proposes a novel way to enhance the retrograded starch content in aged starch paste with no environmental pollution, thereby broadening the application potential of gluten.