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Physical aging of starch, maltodextrin, and maltose
Timothy R Noel1, Roger Parker, Geoffrey J Brownsey
1Institute of Food Research, Norwich Research Park, Norwich NR4 7UA, United Kingdom.
Journal of Agricultural and Food Chemistry
|October 27, 2005
Summary
Physical aging in glassy carbohydrate/water mixtures like maltodextrin/water was studied. Aging increased material stiffness and relaxation time, correlating with thermal properties and predictable by models.
Area of Science:
- Food science and materials science, focusing on the physical chemistry of amorphous solids.
Background:
- Amorphous carbohydrate/water mixtures exist in a glassy state below their glass transition temperature.
- Understanding physical aging is crucial for predicting the shelf-life and stability of these materials.
Purpose of the Study:
- To investigate the physical aging process in low water content amorphous starch/water, maltodextrin/water, and maltose/water mixtures.
- To correlate mechanical properties changes during aging with calorimetric thermal behavior.
Main Methods:
- Mechanical testing, specifically stress relaxation measurements.
- Calorimetry to analyze thermal properties and glass transition behavior.
- Analysis of aging effects at different quench depths below the glass transition temperature.
Main Results:
- Physical aging led to a time-dependent increase in flexural modulus and mechanical relaxation time.
- Mechanical relaxation time increased with deeper quenches and longer aging times.
- Calorimetry revealed an overshoot in heat capacity near the glass transition for aged samples.
- A linear relationship was observed between the logarithm of mechanical relaxation time and the enthalpy change of the heat capacity overshoot.
Conclusions:
- Physical aging significantly alters the mechanical properties of glassy carbohydrate/water systems.
- The observed aging phenomena are linked to changes in molecular mobility and enthalpy relaxation.
- The Tool-Narayanaswamy-Moynihan model effectively describes the calorimetric behavior during physical aging.
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