A comparison of the effects of heat moisture treatment (HMT) on rheological properties and amylopectin structure in sago (Metroxylon sago) and arenga (Arenga pinnata) starches.

The objective of this study was to study and compare the impact of HMT on rheology and textural properties observed between sago and arenga starces, and then related to structural change of amylopectin. The HMT were conducted using the autoclaving method at 20% moisture content and heated to 120 C for 60 min for sago and 90 min for arenga starch as optimum condition. The HMT shifted gelatinization temperature higher and reduced the enthalpy of both starches. The HMT sago starch paste exhibited an exceptionally strong shear thinning behavior as shown by a rapid decrease of viscosity and an increase of shear rate. The HMT clearly made the texture of starch gels more fragile compared to their native form and reduced their breaking point to a lower strain. The HMT effect on the rheological properties and texture of the sago starch was greater than the changes observed with the arenga starch. Major changes in rheological properties after HMT was not followed by changes in amylopectin structure. The HMT process did not significantly affect the amylopectin chain-length distribution in Arenga starch. In the sago starch, HMT affect to long chain amylopectin with DP ≥ 37. The HMT effect on rheology and textural properties was higher in sago starch than arenga starch. This study demonstrated that long chain amylopectin with DP ≥ 37 plays an important role in contributing to the rheological change caused by the HMT.