Variations in Flexural and Compressive Fracture Behavior of a Brittle Cellular Food (Dried Bread) in Response to Moisture Sorption

Mechanical properties of dried bread (a cellular baked product) equilibrated at different water activities (A w ) were measured using three‐point bending and uniaxial compression to compare their responses to moisture sorption. The glass‐to‐rubber transition was clearly demarcated in all the mechanical property‐A w curves, although there were differences in critical A w (0.32–0.56) at which the dramatic changes in mechanical properties occurred. The role of water appeared to be strictly that of a plasticizer where flexural mechanical parameters were concerned, leading to reduced modulus and fracture stress but increased fracture strain with increasing A w . Uniaxial compression tests revealed moisture‐induced mechanical antiplasticization effects on the material in the glassy state which resulted in maximum compressive fracture stress but minimum fracture strain over the A w range from 0–0.56. Compressive modulus apparently was not affected much by moisture sorption up to an A w of 0.43, above which it decreased sharply.