Mechanical and thermal analysis of raisin components

Moisture content is known to change the mechanical properties of raisins. The progressive chemical removal of cell components was carried out to assess their contribution to the overall raisin properties. It was achieved by preparing an alcohol insoluble residue which was then sequentially extracted and its carbohydrate composition analysed. The removal of structure and geometry effects was undertaken by pressing uniform mouldings of the raisin and its insoluble components, which were conditioned over saturated salt solutions at room temperature. Dynamic mechanical thermal analysis (DMTA) of the mouldings indicated their decreasing stiffness with increasing temperature as well as the occurrence of the glass transition, which was complemented by Differential scanning calorimetry (DSC). The data from DSC and DMTA were interpreted in terms of contributions from the raisin cell-wall components and sugars and showed the glass transitions of the cell-wall polymers to be consistent with published results on grapes and wood. (C) 1997 Elsevier Science B.V.