Physical and Molecular Changes during the Storage of Gluten-Free Rice and Oat Bread

Gluten-free bread crumb generally firms more rapidly than regular wheat bread crumb. We here combined differential scanning calorimetry (DSC), texture analysis, and time-domain proton nuclear magnetic resonance (TD H-1 NMR) to investigate the mechanisms underlying firming of gluten-free rice and oat bread. The molecular mobility of water and biopolyrners in flour/water model systems and changes thereof after heating and subsequent cooling to room temperature were investigated as a basis for underpinning the interpretation of TD H-1 NMR profiles of fresh crumb. The proton distributions of wheat and rice flour/water model systems were comparable, while that of oat flour/water samples showed less resolved peaks and an additional population at higher T-2 relaxation times representing lipid protons. No significant crumb moisture loss during storage was observed for the gluten-free bread loaves. Crumb firming was mainly caused by amylopectin retrogradation and water redistribution within bread crumb. DSC, texture, and TD H-1 NMR data correlated well and showed that starch retrogradation and crumb firming are much more pronounced in rice flour bread than in oat flour bread.