Effect of Equilibrium Relative Humidity on the Mechanical Signatures of Brittle Food Materials

Abstract

AbstractThree brittle commercial bakery products (bread sticks, pretzels, and zwiebacks) were compressed after equilibration at five relative humidity levels with a computer‐interfaced Universal Testing Machine. Their mechanical signatures are presented in the form of conventional force—time relationships, power spectra calculated by the fast Fourier transform, Richardson plots from which the apparent fractal dimension was calculated, and displays of the symmetrized‐dot pattern (SDP) produced from the original force—time relationships. It is demonstrated that, although the original force—time relationships were irregular and irreproducible, consistent patterns and values did emerge in the transformed data. Plasticization, as a result of moisture sorption, is clearly expressed in the disappearance of the high‐frequency region of the power spectrum and a drastic decrease in the magnitude of the apparent fractal dimension. The differences among the shapes of the original force—deformation curves before and after moisture sorption are also clearly evident from the SDP displays, but the sensitivity of the method needs to be established with a larger experimental data base.