Analysis of mass transfer parameters (changes in mass flux, diffusion coefficient and mass transfer coefficient) during baking of cookies

Increasing trade of ready to eat foods such as cookies highlights an interest in quality defects (cracking, checking due to non-homogenous moisture distribution) during baking. The most important parameter resulting in adverse quality changes is non-homogenous moisture distribution due to diffusion and external convective mass transfer coefficient. To control and optimize a baking process for quality purposes, actual values of mass transfer parameters should be known. Infinite external convective mass transfer coefficient and constant diffusion coefficient approaches are numerously applied in the literature. However, in natural convection cases, mass transfer coefficient value may not be infinite. In addition, the diffusion coefficient may be time and/or temperature dependent. To compare the finite and infinite external mass transfer and diffusion coefficient approaches, in this study, baking cookies was taken as an experimental case. For this purpose, moisture changes for cookies were estimated based on weight changes and initial moisture contents during baking at 190, 200 and 210 °C. Then, infinite external convective mass transfer coefficient and constant diffusion coefficient value approaches were applied and compared to finite-variable external convective mass transfer coefficient and variable diffusion coefficient value approaches. These values were found to vary during baking, and they were a function of internal cookie temperature changes. It was also concluded that the variation in these values should be determined for effective mass transfer and optimization models.