Combined Effects of Baking Conditions and Bacterial α-Amylases on Staling Kinetics of Degassed and Porous Bread Crumb

Enzymes such as alpha-amylase are extensively used to retard the staling process. Enzymes are acting both during fermentation and during baking. The objective of this work was to determine the relative action of alpha-amylase during fermentation and during baking. The impact of the baking conditions (time, temperature) was also considered. To attain this aim, a degassed bread crumb was baked in a miniaturized system using two programs of baking: heating rates 10.27 and 6.88 A degrees C/min corresponding to 180 and 220 A degrees C baking temperatures, respectively. Mechanical and thermodynamic properties of the degassed crumb were assessed during aging of bread by determining the Young's modulus E, the amount of freezable water, and the melting enthalpy of retrograded amylopectin. A first-order kinetic model was used to determine the different parameters of staling kinetics. Results showed that the hardening of crumb increased during storage. The kinetics were faster for samples baked with fast heating rate than for those baked with slow heating rates. The use of enzymes decreased the Young's modulus but did not have any effect on the staling rate. Calorimetric analysis of the starch retrogradation showed a reduction of the amount of freezable water during storage with an increase of retrograded amylopectin. A comparison between mechanical properties of conventional crumb and of the degassed dough confirmed that experimental data fitted correctly the Gibson and Ashby's model.