Rheological and structural properties of wheat dough acidified by means of a chemical or a biological procedure

Sourdough is the microbial inoculum for many typical Italian baked products. Sourdough fermentation produces a slow acidification due to the progressive production and accumulation of microbial metabolites that induce peculiar aromatic properties and enhance the shelf-life of the product. The effects of the acidification on the structural organization of starch and protein macromolecules are less known. The influence of the acidification (pH range from 5.9 to 4.0), obtained by two different procedures (sourdough process or addition of lactic acid), on the structural and rheological properties of the dough was investigated by means of empiric and fundamental tests. The chemical acidification promotes a progressive decrease of the dough consistency and elasticity, pointed out by the farinographic test. The “weakening” of the protein network is confirmed by a lower storage modulus (G’), evaluated by the frequency sweep test. Moreover, the rheofermentographic test shows a decrease in dough volume and CO2 retention. Other changes related to pH can be observed in starch behaviour during the viscoamylographic test. The biological acidification induced by the sourdough process promotes changes in the protein organization as well. Nevertheless, the front face fluorescence approach underlines the network capacity to maintain a more compact structure even at low pH values. These results indicate that the slow and progressive dough acidification associated with the biological process allows the proteins to organize a network that is more suitable for guaranteeing a higher volume expansion.