| As a method of producing modified starch, heat treatment is simple, safe and has no pollution, but it has significant impact on properties and structure of starch, which has a significant and great prospect in future. For this reason, heat treatment is worth popularizing. In the study, corn starch was modified by heat-moisture, dry heating treatment, and dry heated after blended with food guns using a oven in a dry state, to study effect of heating treatment on properties of starch. Native and modified starches were evaluated for their pasting, sediment volume, and structural properties through Rapid Viscosity Analyzer(RVA), X-ray diffraction(XRD), Fourier Transform Infrared Spectroscopy(FTIR), Scanning electron microscope(SEM) and Differential scanning calorimeter(DSC). The main results were as follows:(1) Heat-moisture treatment decreased solubility of corn starch. Concave holes appeared on appearance of starch granules and starch granules bonded. DSC showed To increased after heat-moisture treatment, but gelatinization enthalpy decreased. RVA showed peak viscosity decreased but gelatinization temperature increased. And higher temperature, longer time made these properties change significantly. XRD showed characteristic peaks overlapped partially and crystallinity declined. However, microcrystalline was nearly no change.(2) After dry heating treatment, properties of starches changed. Compared with native starch, solubility and paste viscosity of modified starches decreased, but pasting temperature increased when treatment temperature was lower than 150 ℃. Modified starches had lower solubility, viscosity, pasting temperature and gelatinization enthalpy when treatment temperature was 150 ℃. Granules of modified starches bonded tightly and there were some holes on its surface after dry heating treatment.(3) Corn starch was modified by dry heating after blended with sodium alginate, xanthan or carboxymethy. Before dry heated, there were no significant changes on whiteness and pasting temperature. Expansion decreased, but peak viscosity increased. After dry heated, pasting temperature of blends increased, but whiteness, expansion, peak viscosity decreased. The changes of starch modified with CMC by dry heating were the most obvious among the three ionic guns.(4) Modified starch wth CMC after dry heating increased pasting temperature and decreased sediment volume. FTIR proved the existence of ester carbonyl group with the absorption at 1714 cm-1, suggesting hydroxyl groups of starch and carboxylate acid groups of CMC formed the ester bonds in heating process. The change of sediment volume indicated crosslinking degree increased when CMC content, temperature and time of dry heating increased. In addition, the XRD showed crystalline structure was nearly no change after dry heating, but an increase of crystallinity was found. |
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