| Unmodified native starches have very limited use in the food industry because of some inadequacies. Therefore, investigation of proper modification processing of starch to fulfill the industrial requirements has been a prevalent urgent realm. The effects of pulsed electric fields on the physicochemical properties of starches(potato, cassava) and starch acetates were studied in this paper. The main conclusions obtained were introduced as follows.1) The effects of pulsed electric fields(PEF) on the structure properties of starches were studied. After being treated by PEF, some coarseness or damage had been generated on the surface of the starch granules. Meanwhile, the relative crystallinity of starches were decreased as the increasing electric fields strength and treatment time. Potato starch is B-type starch and cassava starch Ca-type. However, the PEF treatments did not change the chemical structure and crystal type of starches by FTIR and XRD analysis. The results showed that the relative crystallinity of starches decrease from 29.57% to 29.03%~19.66% and 38.62% to 38.11%~20.29% for potato and cassava respectively.2) The effects of pulsed electric fields on the physicochemical properties of starch pastes were studied. Transparency, freeze-thaw stability of starch pastes were increased, and swelling power and solubility were decreased as the increasing electric fields strength and treatment time. The Brebender viscograms illustrated that PEF-treated starches revealed an increase in pasting temperatures, and a reduction in paste viscosity.3) The effects(the strength of PEF, the reaction time and the concentration of acetic anhydride) of pulsed electric fields treatments on the starch acetates were studied. And the results showed that the amounts of acetyl content and degree substitution(DS) were increased after PEF treatments, indicating that PEF treatments could promote the esterification. Under the experiment conditions, DS was changed from 0.084 to 0.102 and 0.069 to 0.097 for cassava starch acetates and potato starch acetates respectively.4) The effects of pulsed electric fields treatments on the starch acetate granules, structure and crystal type were studied. SEM analysis showed that some coarseness or damage had been generated on the surface of the starch granules. FTIR analysis showed that the acetyl group was reacted with starch granules. Acetylated starches showed some new absorption at 1730, 1374, and 1250 cm-1 assigned to carbonyl C =O, CH3 symmetry deformation vibration and carbonyl C–O stretch vibration, respectively. The relative crystallinity of starch pastes were all decreased as the increasing electric fields strength and treatment time. However, the crystal type of starches did not change.5) The effects of pulsed electric fields treatments on the properties of starch acetate pastes were studied. And compared with the starch acetates without PEF treatment, the paste transparency, freeze-thaw stability, solubility and swelling power were increased, so the stability of paste was improved. The Brebender viscograms illustrated that PEF-treated starch acetates revealed an increase in paste viscosity, and a reduction in pasting temperatures. |
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