Development and characterization of resistant starch produced by an extrusion–debranching strategy with a high starch concentration

Amylose content is the main factor affecting resistant starch type III formation and can be effectively improved by debranching with pullulanase. Nonetheless, low substrate concentration and long treatment time limit the efficiency and yield of this method. We described a new extrusion–debranching strategy that can achieve industrially efficient enzymatic starch debranching to improve amylose and RS contents. Starch was fully gelatinized and partially degraded via first extrusion in a twin-screw extruder. The extruded starch and different amounts of pullulanase were mixed and subjected to a second extrusion, which resulted in the debranching of amylopectin. Tests with corn starch (CS) and pullulanase at 20, 40, 60, 80, and 100 U/g dry starch weight gave extruded corn starch (ECS) and enzymatically debranched ECS (EECS) after the first and second extrusions, respectively. Increasing the pullulanase amount to 100 U/g (EECS-100U) also increased the amylose content to 90.21%, with a starch concentration of 66.6% (w/v). EECS presented a B + V-type crystallinity pattern and showed excellent thermal stability, with melting temperatures of the first and second peaks ranging from 90 °C to 135 °C and from 140 °C to 170 °C, respectively. The short amylose exhibited rapid recrystallization. RS content increased with increasing amounts of pullulanase. EECS-100U exhibited the lowest digestibility, with a 41.50% RS content. These results suggest that the extrusion–debranching strategy for improving amylose content is both feasible and effective. The findings will provide guidance for the continuous industrialized production of amylose, RS, and low glycemic index foods.