Texture and staling of wheat bread crumb: effects of water extractable proteins and 'pentosans'

The increase of crumb firmness prepared from doughs enriched with water-sol uble proteins and/or water-extractable pentosans was investigated at variou s aging times with DSC, to assess starch retrogradation, and with an Instro n dynamometer, to determine the elastic modulus. The crumb enriched in solu ble proteins became firmer, and that with extra pentosans remained softer t han the standard recipe crumb. It was soon evident that neither starch retr ogradation nor water loss (due to the crumb-to-crust migration) were affect ed by the presence of extra proteins and/or pentosans: thus, neither proces s could explain the observed differences in the trends of the elastic modul us. According to image analysis investigations, the protein-rich crumb had narrow and regular alveoli, which were well separated from one another, whe reas a coarser structure was obtained by adding extra pentosans to the doug h recipe. It was, therefore, concluded that differences of crumb firmness m ight be mainly due to the structure formed in the course of leavening and b aking, rather than to starch retrogradation and moisture loss. These proces ses indeed contribute to significantly increase the rigidity of the alveola r walls, but the overall elastic modulus of a sponge-like system, like a br ead crumb, largely depends on the manner in which imposed strains are sprea d through the alveolar structure. Accordingly, for a given rigidity of the alveolar walls, the elastic modulus of the crumb will depend on the size, s hape and distribution of the alveoli. (C) 1998 Elsevier Science B.V. All ri ghts reserved.