Frequency dependence of viscoelastic properties of bread crumb and relation to bread staling

Abstract

The viscoelastic behavior of bread crumb was studied using dynamic mechanical analysis (DMA) in the compression mode with the frequency sweep. The dynamic storage modulus (E′), loss modulus (E"), and tanδ (E"/E′) were measured for bread crumb aged up to three days at ambient temperature. The viscoelastic properties of bread crumb showed a characteristic frequency dependence similar to that of a soft rubberlike solid. Typical behavior of bread crumb involved a transition from rubberlike to glasslike consistency with increasing frequency. At a low frequency region, the E′ and E" values were relatively small and nearly constant, showing characteristics of the rubbery plateau. Then, they increased rapidly with increasing frequencies and approached a glasslike state. Tanδ was low and almost constant at low frequencies before the transition, then went through a prominent peak with increasing frequency. The frequency at which the tanδ of bread crumb started to rapidly increase was defined as the onset frequency (fo) of the transition. The fo values increased with the aging of bread crumb samples, which correlated highly to bread staling (r = 0.942). Both dynamic moduli E′ and E"at fo also increased with the aging of bread, which correlated highly to firmness obtained using a texture analyzer in a static compression mode (r = 0.941 and 0.943, respectively). DMA measurements could be helpful in characterizing bread staling.