Enrichment of soybean dietary fiber and protein fortified rice grain by dry flour extrusion cooking: the physicochemical, pasting, taste, palatability, cooking and starch digestibility properties

With the prevalence of chronic conditions in patients due to a dietary imbalance, the demand for inexpensive, nutritious and high dietary fiber extruded rice is increasing rapidly. However, the factors of quality and bioavailability are still the major constraints to its development. In this study, soybean dietary fiber (DF) and protein fortified rice grain were prepared via dry flour extrusion processing. The results showed that the extruded rice had a similar density to that of natural rice and a significantly lower whiteness degree and transparency. Notably, the cooking texture and palatability of extruded rice were affected by the added amount of DF, resulting in rice with a taste value close to 70 in DF 6–9% (w/w) samples. The pasting properties, microstructure, and molecular interactions according to RVA, SEM and FTIR analyses, respectively, were also significantly affected by the DF content. The soluble dietary fiber was significantly increased from 0.0021 g g(−1) to 0.216 g g(−1) in extruded rice. Importantly, the starch digestibility in vitro showed significantly lower readily digestible starch (RDS) and higher resistant starch (RS) in DF 6–15% (w/w) extruded rice than in natural rice and DF-0 rice, respectively. The glycemic index (GI) was reduced in DF > 6%. In this study, we provide a new high dietary fiber extruded rice product with good texture and palatability, and we reveal the effect of DF on the extruded rice properties.