No abstract

A b s t r a c t. This study presents mathematical modelling of bread moisture loss or drying during baking in a conventional bread baking process. In order to estimate and select the appropriate moisture loss curve equation, 11 different models, semi-theoretical and empirical, were applied to the experimental data and compared according to their correlation coefficients, chi-squared test and root mean square error which were predicted by nonlinear regression analysis. Consequently, of all the drying models, a Page model was selected as the best one, according to the correlation coefficients, chi-squared test, and root mean square error values and its simplicity. Mean absolute estimation error of the proposed model by linear regression analysis for natural and forced convection modes was 2.43, 4.74%, respectively.K e y w o r d s: moisture losing, bread, mathematical modelling INTRODUCTIONAlthough people have practiced baking for a long time, the understanding of the whole process is not very clear. One of the possible reasons for this is that several fundamental complex physical processes are coupled during baking, like evaporation of water, volume expansion, gelatinization of starch, denaturation of protein, crust formation, etc. Several experimental and mathematical models have been developed for clear understanding of baking (Mondal and Datta, 2008).As soon as the product is placed in the oven, water evaporates from the warmer region, absorbing latent heat of vaporization, and the surface layers start drying. Beneath this drying region, water vapour diffuses through the interconnected pores towards the surface, under the influence of the water vapour concentration gradient. A concomitant liquid water gradient is formed and ensures the diffusive transfer of water from the core to the surface. As the diffusive flow of liquid water from the core is less rapid than evaporation flow at the surface, a drying zone is developed which slowly increases in thickness and forms the crust.Whereas bread crust is known to be closely related with moisture loss of bread during baking, the crust formation affects the amount of moisture evaporating from wet dough during the baking process as a thicker crust is produced with a higher moisture loss in bread (Mohd Jusoh et al., 2009;Wiggins, 1999). Besides that, moisture content or water activity of bread surface has an important effect on the beginning of the browning reactions. Purlis and Salvadori (2009) expressed that minimum requirements for the initiation of colour formation are temperature greater than 120°C and water activity less than 0.6. Also, in relating bread crust properties in terms of its colour with moisture loss, Purlis and Salvadori (2007) presented a strong correlation between the moisture loss and the crust colour formation in their study on browning kinetics of bread. From those reports, it seems viable to control moisture loss from bread during baking and to propose moisture loss models in order to predict bread moisture loss behaviour during baking.Mathematic...