ABSTRACT
In this paper, we developed a mathematical model to simulate the heat and mass transfer during the convective drying of injera. The coupled set of heat and moisture partial differential equations (PDEs) were numerically solved by the finite element method (FEM) using COMSOL Multi-physics, 5.5. To validate the simulated results, drying experiments were performed using a tunnel dryer at two air temperatures (313.15 and 333.15 K) and velocities (0.25 and 0.5 ms-1). The predicted versus the experimental results showed a very good agreement with a coefficient of determination, R 2 > 0.95 for both temperature and moisture ratio and a Root Mean Square Error, RMSE < 0.05 for moisture ratio and <3.5 K for temperature. The predicted temperature and moisture ratio distributions of the injera at different times and positions (thickness and diameter) clearly showed the uniformity of drying. The time required to reduce the moisture ratio of injera from 1 (-) to 0.03 (-) at a temperature of 333.15 K, relative humidity of 11% and air velocity of 0.5 ms-1 was 125 min. Both temperature and velocity have a significant effect on moisture reduction when drying was conducted (p < 0.05). The interaction effect between them also indicates a significant difference (p < 0.05) in the moisture removal rate of injera.
ABSTRACT
Additive manufacturing or 3D printing can be applied in the food sector to create food products with personalized properties such as shape, texture, and composition. In this article, we introduce a computer aided engineering (CAE) methodology to design 3D printed food products with tunable mechanical properties. The focus was on the Young modulus as a proxy of texture. Finite element modelling was used to establish the relationship between the Young modulus of 3D printed cookies with a honeycomb structure and their structure parameters. Wall thickness, cell size, and overall porosity were found to influence the Young modulus of the cookies and were, therefore, identified as tunable design parameters. Next, in experimental tests, it was observed that geometry deformations arose during and after 3D printing, affecting cookie structure and texture. The 3D printed cookie porosity was found to be lower than the designed one, strongly influencing the Young modulus. After identifying the changes in porosity through X-ray micro-computed tomography, a good match was observed between computational and experimental Young's modulus values. These results showed that changes in the geometry have to be quantified and considered to obtain a reliable prediction of the Young modulus of the 3D printed cookies.
ABSTRACT
The moisture sorption isotherm at three maturity levels of the M a reko Fana chili pepper variety (red, brown and green) has been studied in this paper. The sorption isotherm was determined based on the standard static gravimetric method using a glycerol-water mixture in a relative humidity range of 10-92% at three temperature levels and nonlinear regression analysis was used to select suitable sorption models. The Clasius - Clapeyron equation was implemented to determine the isosteric heat of sorption of the chili pepper using the experimental equilibrium moisture content at different sorption temperature levels. The results showed that the GAB model was well fitted for green chili pepper, while the OSWIN model described well the brown and red chili variant. There was a difference in net isosteric heat between the adsorption and desorption isotherm of chili pepper maturity. For green chili, the maximum value of the net isosteric heat was 18 kJ mol-1 and 20 kJ mol-1 for adsorption and desorption isotherms, respectively and it decreased exponentially as moisture content increased. The desorption heat was higher than the adsorption heat for each maturity of chili pepper which indicated the existence of hysteresis in the sorption process. In comparison to literature data reported for different chili varieties, M a reko Fana has a lower heat of sorption and monolayer moisture content.
ABSTRACT
A permeation-diffusion-reaction model was applied to study gas exchange of apple fruit (Kanzi, Jonagold, and Braeburn) as effected by morphology and respiratory metabolism. The gas exchange properties and respiration parameters of the fruit organ tissues were measured. The actual internal tissue geometry of the fruit was reconstructed from digital fruit images and the model was solved over this geometry using the finite element method. The model was validated based on measurements of internal gas concentrations and the gas flux of the fruit to its environment. Both measurements and an in silico study revealed that gradients of metabolic gases exist in apple fruit, depending on diffusion properties and respiration of the different cultivars. Macroscale simulation confirmed that Jonagold has large potential for controlled atmosphere (CA) storage while low diffusion properties of cortex tissue in Braeburn indicated a risk of storage disorder development. Kanzi had less O(2) anoxia at CA storage compared with Braeburn.
