Effect of non-starch polysaccharides and butterfly pea flower on the in vitro digestibility of glutinous rice

• Butterfly pea flower and non-starch polysaccharides coat rice grains. • Interactions among starch, pea flower and polysaccharides affect layer properties. • Physicochemical properties of glutinous rice are affected by these coating layers. This study investigated the impact of a proprietary blend of non-starch polysaccharides (C5), butterfly pea flower powder (BPF), and their combinations on glutinous rice (GR) properties and digestibility. The C5 blend comprised of xylooligosaccharides, barley β-glucan, konjac glucomannan, xanthan gum, sodium alginate, and low-methoxy pectin. The results showed that adding C5 and BPF to GR decreased its swelling power by 4.6 % to 40.5 % and solubility index by 1.1 to 6.6 times. In addition, BPF significantly increased GR pasting viscosities. Both the additives also affected the hardness and adhesiveness of cooked GR samples, with varying effects depending on the types and concentrations of additives used. In digestive properties, both C5 and BPF reduced total digested starch by 2.6 % to 9.7 % and lowered the hydrolysis index by 2.0 % to 7.9 %. However, at higher BPF concentrations (3 % and 5 %), this effect on starch digestibility diminished, which is a phenomenon not observed with C5-BPF combinations. The findings suggest that C5 and BPF influenced the digestibility and textural properties of GR through their interactions with starch molecules and ability to form a protective layer around the rice grains. This study provides valuable insights into strategies for lowering the glycaemic response of glutinous rice products.