Staling of gluten-free breads: physico-chemical properties and 1H NMR mobility

Four gluten-free (GF) breads produced using commercial GF mixes with different formulations were characterized during 1 week of storage and compared to wheat-flour-based bread (STD), in terms of texture (texture profile analysis), amylopectin retrogradation (differential scanning calorimetry) and water status (moisture content, frozen water content by differential scanning calorimetry and H-1 nuclear magnetic resonance-NMR mobility by a low-field spectrometer). GF fresh breads were significantly harder, less cohesive and less springy than STD. Water status indicated higher water availability in GF breads, depending on formulation, with higher moisture and frozen water content that was also reflected in a higher molecular mobility (H-1 spin-spin NMR relaxation time). Furthermore, limited changes in moisture and frozen water contents were observed in GF bread, and therefore, textural changes in these GF products were mostly related to retrograded amylopectin. Statistical analysis with PCA (principal component analysis) allowed to identify the most important factors in the GF bread staling process. The effect of formulation (GFs vs STD) was related to water status descriptors and the effect of storage to textural properties, retrograded amylopectin parameters, as well as the mobility of the more rigid protons.