Staling of potato and wheat steamed breads: physicochemical characterisation and molecular mobility

To clarify the physicochemical characterisation and water status of potato steamed bread (PSB) and wheat steamed bread (WSB) during the staling process, texture, amylopectin retrogradation, crystalline structure, water migration and microstructure were evaluated by texture analysis, differential scanning calorimetry, X-ray diffraction, nuclear magnetic resonance (H-1 NMR) and scanning electron microscopy (SEM). Results showed that starch molecules in PSB and WSB were recrystallised and formed B-type starch, which had a positive correlation with hardness and thermal enthalpy. Compared to WSB, PSB had a relatively low B-type crystallinity; moreover, a smaller decrease of free water in PSB was also detected in the NMR test, which indicated that more moisture can be used to plasticise crumb, thus contributing to a softer texture of PSB. SEM revealed that the amount and size of the cracks on the interface of starch and gluten matrix in WSB increased with the prolongation of storage time.