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Effect of the starch concentration on phase transitions of starch dispersions prepared with a glycerol solution or pure glycerol.

Author(s) : SOBRAL P. J. do A., HABITANTE A. M. Q. B., CARVALHO R. A. de, et al.

Type of article: Article

Summary

The objective of this work was to study, using a calorimetric method, the effect of the starch concentration on the phase properties of cassava starch dispersions, prepared using a glycerol solution and pure glycerol. Starch dispersions (SD) were prepared with 10-70 g of starch 100/g of SD using either a 20% glycerol solution (GS) or pure glycerol (PG). These dispersions were analyzed with a differential scanning calorimeter. The water activity of these samples was also determined at 25°C. At low temperatures, the glass transition (Tg) was well defined in samples prepared with 10-50% of starch, but was not so for SDs with 70% starch, for both glycerol solutions. For SD prepared with GS, an increase in starch concentration from 10 to 70% caused a reduction in Tg, but for SD with 10-50% starch and prepared with PG, the Tg remained constant, increasing slightly for samples with 70% starch. This behaviour agreed with that of the water activity, which increased when the starch concentration increased from 10 to 70% for SDs prepared with GS. In the intermediate temperature domain, for the SD with GS, an endothermal peak was visible near zero degrees due to the melting of ice, but this transition was not seen with PG. At relatively high temperatures, starch gelatinization was observed in all the DSC curves, while in the case of samples with PG, an exothermal peak was also seen before the endothermal one. The starch gelatinization temperature (Tsg) remained essentially constant for samples with 10-50% of starch, increasing for a concentration of 70%. When the starch dispersing agent was PG, it was observed that a decrease in the starch concentration from 70 to 50% also caused an important reduction in Tsg. However, in more dilute starch dispersions, the Tsg increased. Thus it was concluded that some physical interactions may take place between the glycerol and the glucose molecules of the cassava starch even before its gelatinization.

Details

  • Original title: Effect of the starch concentration on phase transitions of starch dispersions prepared with a glycerol solution or pure glycerol.
  • Record ID : 2009-1701
  • Languages: English
  • Source: Braz. J. Food Technol. - vol. 11 - n. 4
  • Publication date: 2008/10

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