Physical aging of processed fragmented biopolymers

Low moistures foods containing starches exhibit a sub-Tg endotherm (55–60 °C) when they are stored at constant temperatures. Although the origin of the endotherm is still debatable, it has been attributed to the water–hydroxyl group interactions and/or enthalpic associations between water and carbohydrates. In the present study, physical aging of the starch components of corn flakes prepared with two different levels of starch fragmentation was studied using thermal and rheological methods. A sub-Tg endotherm was observed at temperatures around 50–60 °C by both DSC and Oscillatory Squeezing Flow measurements. An increase of 1.5% of moisture content was observed for both fragmented flakes during aging. The temperatures at which the sub-Tg endotherms occurred were independent of aging and moisture content increase during storage, whilst enthalpy increased with both aging time and moisture content. Although the moisture content of the two types of flakes were different the aging time at which the first endotherm appeared and the rate at which the enthalpy increased were dependent only on the level of starch fragmentation. Corn flakes with a high level of starch fragmentation required a longer period of aging time before the presence of the endotherm could be detected and had a greater rate of increase in enthalpy. Overall, flakes having higher starch fragmentation absorbed more water, and the percent of water uptake decreased with aging time. Flakes with low starch fragmentation exhibited little to no change in water uptake during aging.