Physicochemical properties of heat moisture treated sweet potato starches of selected Indonesian varieties

The study was aimed to modify sweet potato starches (SPS) of Indonesian varieties to be suitable for starch noodle production. SPS were isolated from four varieties, namely Sukuh, Cangkuang, Jago and Papua Salosa. The native SPS were adjusted to moisture content of 25% and exposed to heat moisture treatment (HMT) at 110°C for 3, 4 and 5 h. The native and treated starches were characterized for swelling power, solubility, gel hardness, pasting properties and microstructure. The results indicated that HMT reduced the swelling power and solubility, eventhough the length of treatment did not affect both properties. Except in Papua Salosa, HMT increased gel hardness with the longer treatment time resulted in less increase. HMT increased pasting temperature, and longer treatment time led to higher increased value. HMT reduced peak viscosity, and the longer treatment resulted in the higher reduction. The final viscosity of treated starches was higher than the native ones, except for Papua Salosa. The highest final viscosity with a significant increment was shown by Sukuh (517.5 RVU) treated for 4 h. Longer HMT led to a slightly decrease in final viscosity. In general, HMT clearly shifted SPS from Type A to Type C of amylographic patern, except for Papua Salosa. Photomicroscopy showed that the forms of SPS granules of all varieties were spheric. HMT did not modify the form and size of the starch granules. The greatest effect of HMT on the physicochemical changes was observed in SPS from Sukuh, followed by Jago and Cangkuang varieties. It could be concluded that heat moisture treated Sukuh starch for 3 h was recommended for noodle production.