| Freeze-thawing cycles treatment can influence the quality of starch products. At home and abroad, the change mechanism about corn starch product freeze-thawing characteristics is less reported, so the study about the effect of freeze-thawing treatment on physicochemical properties and structural properties is more important. The main results are as follows:(1) The normal corn starch gels presented a porous structure after gelatinization, but waxy corn starch gels appeared a layer structure after two times freeze-thawing cycles, and the pore number and layer distance decreased with the increase times of freeze-thawing cycles.After freeze-thawing treatment, the crystalline type of corn starch gels translated into B-type from A-type. With the times increased of freeze-thawing treatment, the crystalline degree decreased after an increase firstly. Compared with the original starch, the absorption peak of-OH and C-O-C of gels significantly shift to the left and the right, respectively.Freeze-thawing treatment had no significant influence on iodine blue value, iodine binding force, the maximum absorption wavelength and amylose content of two gelatinized corn starch. The freeze-thawing stability and hardness of the two kinds of starch gels enhanced and increased. With the increase times of the freeze-thawing cycles, the transparency, water holding capacity, RDS and SDS content of the gelatinized normal corn starch decreased, while there was an increase effect on solubility, swelling degree, hydrolysis rate and RS content, and all of the viscosity property values showed a decrease firstly and then increased, the springiness of normal corn starch gel increased firstly and then decreased.The gelatinized waxy corn starch showed a higher pasting temperature, springiness and adhesiveness, and a lower transparency, holding capacity, solubility and swelling degree after freeze-thawing treatment. The viscosity values, peak time, breakdown and setback presented a first increase and then decreased, the cohesiveness showed an opposite effect. whereas, there was no significant effect on RDS, SDS, RS content and hydrolysis rate could be found after freeze-thawing cycles treatment.(2) With the increase times of the freeze-thawing cycles, hores on the surface of starch granules and the number of pits increased, while the number of bulges of the high amylose corn decreased, and the surface appeared to be rough. After freeze-thawing cycles treatment,the crystallinity of normal corn starch and high amylose corn starch decreased, while waxy corn showed the opposite.The water holding rate and hydrolysis rate increased with the time of freeze-thawing cycles increased, but other parameters had no signigicant change among different times and temperature of freeze-thawing cycles. At-20 ℃, with the times of freeze-thawing cycles increased, the viscosity values, breakdown and setback of the normal corn starch decreased with a higher peak time. At the same time, the peak viscosity and final viscosity increased firstly and then decreased. At-40 ℃, there was a gradually increased trend about viscosity values, breakdown and setback of normal corn starch. Moreover, at-80 ℃, the final viscosity and setback increased. At-40 ℃ and-80 ℃, the viscosity values and breakdown of waxy corn starch gradually increased with a decreased setback.In conclusion, the impact of freeze-thawing cycles treatment on corn starch gel was greater than the starch granule. In the condition of freeze-thawing cycles treatment, the retrograded starch was formed by starch molecules showed recrystal, which resulted in the gel turning harder and the product quality degrading. However, freezing expansion pressure damaged starch granule structure, but not enough to lead to substantial changes in the physicochemical properties of starch granules. |
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