Structural and rheological properties of modified sago starch (Metroxylon sagu) using treatment of steam explosion followed by acid-hydrolyzed as an alternative to produce maltodextrin

The effects of steam explosion (SE) treatment, acid hydrolysis (AH), and the combination of steam explosion and acid hydrolysis treatment (SE+AH) on structural and rheological properties of sago starch were investigated. Steam explosion (SE) is a hydrothermal pre-treatment in high-pressure which caused the expansion of water vapor and hydrolyzing the material into low molecular weight. It is a potential method for changing the structural and functional properties by hydrolyzing the starch with low cost and environmentally friendly. Sago starch and distilled water (1:12) were added into a cylinder of SE reactor at 140°C. The slurry was exploded when the temperature reached. And then sago starch was hydrolyzed in hydrochloric acid at 50°C, 60°C, 70°C for 1, 1.5, 2 h. The solubility, dextrose equivalent, hygroscopicity, viscosity, crystallinity, and rheological properties of acid-hydrolyzed sago starches (AH) were analyzed. Steam explosion (SE) treatment increased the solubility up to 40.1%; meanwhile, the combination of SE+AH increased the solubility up to 70.8%. While the viscosity decreased with increasing degree of acid hydrolysis (i.e. from 2155 cP to 27 cP). The results showed that combination SE+AH could be an effective method to produce maltodextrin. The combination of SE+AH at 70°C for 2 h has dextrose-equivalent value was increased up to 11.97 almost similar to the dextrose equivalent of maltodextrin. It changed the morphology and decreased the crystallinity up to 9.6%. Thus, SE+AH methods could be used to modify properties of starch for a specific product such as maltodextrin.