Modeling of simultaneous heat and moisture transport in cake during baking requires accurate knowledge of thermal properties such as thermal conductivity, heat capacity and thermal diffusivity. These parameters mostly depend on density, composition (particularly, moisture content) and temperature. These properties not only change as baking proceeds but also affect thermal properties reciprocally. In spite of this, many investigators measured and predicted the thermal properties of bakery products ignoring the fact that density, moisture content and temperature have a combined effect on thermal properties.
The objectives of this work were to determine the thermal properties of a cup cake under simulated industrial baking conditions and to determine prediction equations for thermal conductivity, heat capacity and thermal diffusivity based on experimental data.
During baking the temperatures inside the cake were recorded. Samples were taken from the oven (167°C) after 0, 4, 6, 13, 15 and 19.5 min of baking. Thermal conductivity and heat capacity were measured with a line heat source probe and a modulated differential scanning calorimeter, respectively, at the temperature corresponding to the baking time. Thermal diffusivity was estimated as the thermal conductivity divided by the product of heat capacity and density.
In the range of density (D), 803 to 235.7 kg/m3, temperature (T) 20-104 °C and moisture content (M) 0.346 to 0.276 (wet basis), the prediction equations were: for thermal conductivity (k, W/mK)=0.31245M+2.281E-4D+5.887E-4T-0.09642 (r2=0.984), for heat capacity (Cp, J/kgK)=1958.6M+2.7672T+1784.03 (r2=0.997), for thermal diffusivity (a, m2/s)=2.5504E-8M-1.7523E-10D-3.9503E-10T+2.4217E-7 (r2=0.971). Traditional mass fraction model for heat capacity (Cpcal) did not fit our experimental data (Cpmea) well, Cpcal=2.504Cpmea-3867.8 (r2=0.724).
Simulation of heat transfer during baking can be used in the design of optimal process conditions. The results of the present work will be useful in the simulation of heat transfer studies of cup cakes in industrial baking situations.