Low Temperature Freeze-thawing Behavior Of Corn Starch Granule

The freeze-thawing behavior of corn starch granule is a serious problem for corn starch modification and its products further developing, however, few reports have been researched on the freeze-thawing behaviors of corn starch. Therefore, in the present research, we focus on these objects,(1) granule structure and properties of corn starch,(2) the impacts of low temperature freeze-thawing on the structure characteristics of corn starch granule,(3) the effects of low temperature freeze-thawing on the physicochemical and functional properties of corn starch granule,(4) the modification mechanisms of corn starch granule during low temperature freeze-thawing process.Corn starch is classified to waxy and non-waxy corn starch. In the present study, we choose waxy and non-waxy corn starch as the materials, which contained amylose contents are 1% and 30.47%(up to total starch), respectively. The XRD pattern of native corn starch is A type. Native corn starch granules are polygonal and oval, and there are some micro-poles on the granule surface. Turbidity of waxy corn starch pasting solution is lower and decreased with storage time, however, the turbidity of non-waxy corn starch is higher and increasing quickly. Water binding capacity values of waxy and non-waxy corn starch are 2.06 and 1.84, respectively. The results of DSC indicated that the onset temperature, peak temperature and thermal enthalpy of waxy corn starch are about 66.27℃, 71.52 and 22.95 J/g, respectively. ℃However, non-waxy corn starch is 66.22℃, 70.91 ℃and 13.12 J/g, respectively. Texture results indicated that there are significant differences between waxy and non-waxy corn starch. And the DSC scanning results indicated that non-waxy corn starch gel is easy to retrograde during storage.Low temperature freeze-thawing have significantly influences on the structure of corn starch granule. The micro-poles increased and partly are broken after freeze-thawing process, moreover, the starch granule changed from smooth to coarse during the process. After 1 cycle of freeze-thawing process, the granule surface changed at-20 freezing℃, while surface have some changes under-196 freezing-thawing. When freeze-thawing 20 cycles, the granule surface changed significantly and broken under-20 ℃freezing-thawing, while surface changed but not significantly under-196 freezing-thawing. Moreover, the waxy corn starch granule is easy to break.Multiple freeze-thawing cycles have significantly influence on the physicochemical and functional properties. Freeze-thawing cycles didn’t change the A type of corn starch granule, the crystallinity intensity decreased with freeze-thawing cycles. Intensity changed significantly under-20 ℃freeze-thawing process, however, no significantly changed under-196 freeze℃-thawing process. Freeze-thawing process changed the turbidity, swelling power, and solubility of corn starch. Freeze-thawing process can decrease the onset, peak temperature and thermal enthalpy, but have little effects on the retrogradation properties of corn starch. Most important, the freeze-thawing process can increase the absorbing capacity and specific surface of corn starch granule.The modification mechanisms of corn starch during freeze-thawing process, which is caused by the micro-mechanical swelling power and penetrate pressure power together. During the freezing process, water molecule frozen and the volume increased, which produce micro-mechanical swelling power and destroyed the structure of corn starch granule. During the thawing process, water molecule move and re-distribution which produce pressure power, and destroy the structure and properties of corn starch granule.