Effect of heat moisture treatment and partial acid hydrolysis on the morphological, functional and pasting properties of sweet potato starch

Sweet potato starch was modified by partial acid hydrolysis (PAH) and heat-moisture treatments (HMT) at different moisture content and temperature (HMT1: 20% moisture, 90 °C; HMT2: 20% moisture, 110 °C; HMT3: 30% moisture, 90 °C temperature; HMT4: 30% moisture, 110 °C). Modification was also done by combination of HMT and PAH (HMT-PAH1: 20% moisture, 90 °C; HMT-PAH2: 20% moisture, 110 °C; HMT-PAH3: 30% moisture, 90 °C; HMTPAH4: 30% moisture, 110 °C). Pasting, functional, morphological and chemical properties of native and modified sweet potato starches were evaluated. Starch granules of native, single PAH, combined HMT-PAH2, HMT-PAH3- treated starches had identical granular sizes and smooth surfaces while other modified starches showed a rough surface with visible cracks. PAH promoted aggregation while combination of HMT and PAH treatments increased unevenness and rough surface on the starch granules. The peak and setback viscosities decreased in all modified starches while modification increased pasting temperature and pasting time. Functional properties of HMT treated samples were significantly (P < 0.05) affected by different temperatures. Combination of HMT and PAH at 110 °C with 30% moisture content improved the water absorption, oil absorption while solubility index and swelling power of all modified starches were lower than native starch. Generally, starch modified using HMT may be more useful in food systems where high final and peak viscosities are desirable, while PAH and combination of HMT and PAH may find application in processing operations requiring rigid gels such as in hard candies.