Effect of Freeze-thawing Cycles on the Physicochemical Properties of Corn Starch Gels and Granules
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Abstract:
Normal and waxy corn starch gels were subjected to different numbers of freeze-thaw cycles (zero, one, two, three, four, five, and six times) and the changes in their physicochemical properties were analyzed. The scanning electron microscope (SEM) was used to analyze the microstructural properties of corn gels, and iodine blue value, iodine binding force, maximum absorption wavelength, transparency, water holding capacity, solubility, swelling degree, hydrolysis characteristics, and in vitro digestibility of the gelatinized starch were also determined. The results showed that normal corn starch gels had a porous structure after gelatinization, while waxy corn starch gels had a layered structure after two freeze-thawing cycles. The pore size and layer distance decreased with increasing number of freeze-thawing cycles. Freeze-thawing had no significant effect on the iodine blue value, the iodine binding force, the maximum absorption wavelength, and the amylose content of both gelatinized corn starch samples. As the number of freeze-thawing cycles increased, there was a decrease in the transparency, water holding capacity, and content of rapidly digestible starch (RDS) and slowly digestible starch (SDS) in the gelatinized normal corn starch, while there was an increase in the solubility, swelling degree, degree of hydrolysis, and resistant starch (RS) content. The gelatinized waxy corn starch showed decreased transparency, holding capacity, solubility, and swelling degree after freeze-thawing treatment, whereas there were no significant changes in RDS, SDS, and RS content as well as degree of hydrolysis after the treatment.
