Influence of the Starch Content on Swelling in Water - METTLER TOLEDO

Influence of the Starch Content on Swelling in Water

Sample

Potato starch

 

Conditions

Measuring cell: DSC30 

Pan: Aluminum standard 40 µl, hermetically sealed

Sample preparation: Preparation of the starch suspensions by the addition of varying amounts of distilled water; stirring (Ultra-Turrax for 1 min);homogenized suspension weighed into the pan. 

DSC measurement: Heating from 20 °C to 110 °C at 5 K/min

Interpretation

One of the most decisive factors in the swelling of starch is the starch/water ratio. With an excess of water (more than 4 molecules of water per anhydroglucose unit), the endothermic peak is only about 10 K wide, (see also previous example with 20% starch in water). If the starch/water ratio rises above a value of 40%, the reaction range broadens or a second endothermic peak is formed. Whereas the first peak (between 60 °C and 80 °C) appears at constant temperature, a reaction at higher temperatures is evident, which initially leads only to the formation of a shoulder on the first peak and the blurring of the temperature range of the reaction but then, at higher ratios, to the appearance second peak. The area of the first peak decreases, but the total enthalpy remains the same.

Whereas in the limiting case of excess water (40% starch) in the above measurement the endothermic peak lies between 60 °C and 70 °C, the overall reaction at 70% starch extends over a range of 30 K.

At high water contents, the system is destabilized through hydration (water uptake). Increased motion of the polymer chains (heat uptake) and melting of the starch granules begins (first endotherm). In more concentrated starch solutions, this effect is reduced as a result of the limited water content. Direct thermic melting of the starch granules occurs at higher temperatures.

Conclusion

These curves show that the water/starch ratio is important for reproducible results. We recommend weighing starch and water directly into the pan (no mixing required, diffusion adjusts local gradients)

 

Influence of the Starch Content on Swelling in Water | Thermal Analysis Application No. HB 1010 | Application published in METTLER TOLEDO TA Application Handbook Food