In vitro digestibility of different types of resistant starches under high-temperature cooking conditions

Resistant starch (RS) is commercially available as an important category of functional food ingredients. Starch tends to lose the enzymatic resistance upon heat treatment; however, there is a dearth of knowledge on how thermal treatment, especially high-temperature processing, influences the digestibility of different types of RS. In this study, two high-amylose maize starches (HA50 and HA70; RS2), Novelose 330 (RS3), and two cross-linked phosphorylated wheat starch (Fibersym and FiberRite; RS4) were cooked using Rapid Visco Analyzer 4800 at 95, 120 and 140 °C, and their in vitro digestibility was determined after 0.5 and 2.0-h storage at room temperature. The cooking step substantially reduced the enzymatic resistance of RS2, with the lowest RS contents being determined at 120 °C cooking upon 0.5-h storage. Generally, 2.0-h storage enhanced the enzymatic resistance of RS2 cooked at 120 and 140 °C, resulting from stronger re-association and retrogradation between starch molecules during the storage. In contrast, cooking over 95–140 °C did not considerably alter the RS contents of Novelose 330 and FiberRite, indicating their greater stability against high-temperature processing. Moreover, 2.0-h storage did not appear to further increase the enzymatic resistance of cooked RS3 and RS4. The relationships between the digestibility of cooked RS2-4 and their thermal, pasting and gelling properties were thoroughly discussed to elucidate the mechanisms contributing to the enzymatic resistance of the different types of RS under the examined conditions. The fundamental knowledge acquired from this work will be meaningful for the development and utilization of RS ingredients in food products processed under high-temperature conditions.