Boosting Resistant Starch Type 3 in Amylotype Corn Starches via Combined Debranching and Extrusion Treatments

Resistant starch (RS), particularly type 3 (RS3), has garnered significant interest in food science due to its health benefits and functional versatility as a dietary fiber in processed foods. In this study, the combined effects of extrusion cycles and pullulanase debranching on RS3 formation in high-amylose corn starches were investigated. Starch–water (1:10) mixtures were autoclaved, treated with pullulanase, dried, and extruded at 50%, 60%, and 70% of feed moisture contents (100 rpm, 140°C). Solubility and water-binding capacity increased with extrusion compared to native starches, though emulsion properties were not similarly improved. All samples exhibited B+V-type crystallinity. While the type of crystallinity remained unchanged, relative crystallinity slightly increased with more extrusion cycles. Among the different extrusion feed moisture contents studied, 60% feed moisture resulted in extrudates with the highest RS3 content. RS3 content reached to 45.8% in Hylon V and 51.7% in Hylon VII after the starches were autoclaved, pullulanase-treated, and extruded at 60% moisture content for the third time (i.e., third extrusion cycle). However, there was no significant difference between the RS3 contents of the samples obtained after the second and the third extrusion cycles, indicating that more extrusion cycles do not always translate to higher RS3 concentrations. The high RS3 levels, combined with improved functional properties and thermal stability, suggest strong potential for incorporating these starches into food products as high-value dietary fiber ingredients.