The role of bread in economy and nutrition of human life has always been inevitable. Among the Iranian breads, the Sangak bread has a distinguish nutritional value and a special taste with great potential for industrial production. Baking is one of the important and complex processes in bread making. Many phenomena such as evaporation, dough volume rising, starch gelatinization, protein denaturation and crust forming occur in baking. This research was carried out for better understanding these phenomena. In the first part of this work, the impact of fermentation time, baking temperature and time on the quality properties of Sangak bread (pores distribution, apparent volume, density, water activity, crust and crumb firmness, and crust color) was determined. The results showed that: I) increasing the baking time reduces the moisture content, water activity, density, crumb firmness and crust lightness, and increases volume, porosity, crust firmness, a and b. II) increasing the fermentation time increases the volume, porosity and a, b and L, and III) increasing the baking temperature reduces density, moisture content, water activity and L, and increases the porosity, volume, crumb and crust firmness, a and b. In the second step, a multiphase model for simultaneous heat and mass transfer in porous medium was developed to simulate the baking process for part baked Sangak bread. The model was based on Fourier’s law for conductive heat transfer and Darcy’s and Fick’s laws for mass transfer of liquid (water) and gas (water vapor and CO2) phases. Numerical Finite Element Method (FEM) scheme was used to solve the equations. The numerical procedure was implemented in COMSOL Multi physics v3.5 software. Then, thermophysical properties (thermal conductivity, specific heat, enthalpy, initial freezing temperature and density) of Sangak bread during baking were determined and modeled. One of the most important thermophysical properties is thermal conductivity. A line-heat source probe was used to measure thermal conductivity. According to experimental data, thermal conductivity decreases during baking as porosity increases and moisture content decreases. To model the thermal conductivity, four predictive models for porous food were selected and developed (series, parallel , Krischer and Maxwell models). The effective thermal conductivity predicted by Krischer model was in good agreement with the experimental data. Finally, to validate the model, the predicted temperature profiles in different parts of bread were compared with experimental results. Results showed a good agreement between experimental and numerical results. Key word Bread baking, Color, Density, firmness, Modeling, Moisture content, Porosity, Thermal conductivity, Volume, Water activity.
