The effect of sorghum flour (Sorghum bicolor [L.] Moench) on bread staling: From macroscopic to molecular properties

Sorghum is a cereal of a great interest due to its climate resilience and valuable nutritional profile (high content of bioactive compounds). The inclusion of sorghum flour in staple foods such as bread is a strategy to improve breads nutritional value but, at the same time, a technological challenge. Bread staling assessment is an important task to assess the quality of sorghum-composite breads. To date, the literature on this topic is scarce. Therefore, the aim of this work was studying the staling process (over 7 days of storage) in conventional wheat bread (STD) and breads in which 10 (S10), 20 (S20) and 30% (S30) of wheat flour was substituted with sorghum flour. Bread staling was studied considering macroscopic (specific volume, texture, moisture content and water activity), mesoscopic (freezable water content and retrograded amylopectin) and molecular sup(1)H NMR molecular mobility) properties. An increase of hardness and a reduction of specific volume, cohesiveness and springiness were found in S-breads. Moreover, both a higher freezable water content and sup(1)H T2 mobility (for the population at highest mobility), and a lower sup(1)H FID mobility (for the population at lowest mobility, related to rigid starch domain) were found in S-breads. The presence of the biopolymers such as kafirin proteins, fibre, and poorly accessible starch, may have weakened the solids-water interactions in fresh S-products. These changes were evident during all storage time. Alternative strategies could be applied to improve sorghum bread quality and stability during storage, such as fermentation with proteolytic and exopolysaccharides-producing lactic acid bacteria strains.