Effects of amylose content, autoclaving, parboiling, extrusion, and post-cooking treatments on resistant starch content of different rice cultivars

Abstract

Experiments were conducted to examine the effects of parboiling, extrusion, rice variety, rice : water ratio, and cooling after cooking on the resistant starch (RS) content of rice. When uncooked the medium-grain rice (Amaroo) contained less amylose (18.8 g/100 g, P = 0.001), higher fast digestible starch (FDS) content (21.7 g/100 g, P < 0.001), and less RS (0.1 g/100 g, P < 0.001) than the long-grain rice (Doongara) (25.6, 15.9, 0.4, respectively). Parboiled rice had the highest FDS (33.9 g/100 g) and RS (0.72 g/100 g) contents, with an amylose content of 25.4 g/100 g. The effects of rice type, rice : water ratio (1 : 1 or 1 : 2 w/w), and post-cooking interventions (freshly dried or dried after cooling for 24 h at 4°C) on the RS content of rice cooked in an autoclave were examined. The RS contents were significantly different among the rice types (0.6, 1.4, 3.7 g/100 g for Amaroo, Doongara, and parboiled rice, respectively, P < 0.001). Decreasing the rice : water ratio (1 : 2) and cooling (24 h at 4°C) after cooking significantly increased the RS content (P < 0.001). Extrusion decreased the RS content in the high RS rice only (0.42–0.16 g/100 g, P = 0.02). The results indicate that parboiling rice, and the use of a higher-amylose-content rice, a lower rice : water ratio, and cooling after cooking all increase RS content, whereas extrusion decreases the RS content of rice.