Osmotic dehydration kinetics of banana slices considering variable diffusivities and shrinkage

This article studied the use of diffusion models to describe variation of water quantity and sucrose quantity during osmotic dehydration of bananas cut into cylindrical slices. Bananas with radius of 1.7 cm and 18 °Brix (on average) were cut into 1.0 cm of thickness. A solution was proposed for the diffusion equation in cylindrical coordinates using the finite volume method, with fully implicit formulation. The diffusion equation was discretized assuming diffusivities and dimensions with variable values for the banana slices. Boundary conditions of the third kind have also been considered. The osmotic dehydration experiments were conducted in binary solutions (water and sucrose) under conditions of 40 and 60 °Brix and temperatures of 40 and 70°C. Mathematical modeling was proposed to describe the processes presented good results for water quantity and sucrose quantity, with good statistical indicators for all fits.     

Evaluation of Mathematical Models for Prediction of Thin-Layer Drying of Banana Slices

Drying characteristics of bananas were experimentally determined. The drying experiments were carried out in a hot air dryer at four inlet temperatures of 50, 60, 70 and 80°C, at a constant air velocity of 2.4 m/s and relative humidity of 4–25%. The experimental results were fitted to five thin-layer drying models and it was found that the Page and Logarithmic models gave better fit that the other models. Values of the effective diffusivity ranged from 7.374 × 10^?11 to 2.148 × 10^?10 m²/s. Activation energy for moisture diffusion of the banana slices was found to be 32.65 kJ/mol.     

Prediction of moisture transfer parameters for microwave drying of lactose powder using Bi–G drying correlation

The mass transport properties characterising the drying of lactose powder were determined using a correlation proposed by Dincer and Hussain [Dincer, I. & Hussain, M. M. (2004). Development of a new Bi–Di correlation for solids drying. International Journal of Heat and Mass Transfer, 47, 653–658]. Experimental moisture content data for lactose samples dried under convective, microwave, combined convective-microwave and combined vacuum-microwave conditions were collected. The drying coefficients and lag factors were calculated from the experimental data and incorporated into the model. The Bi numbers were in the range 0.185–439, and moisture diffusivities and diffusion coefficients in the range from 0.135 × 10⁻⁹ to 102 × 10⁻⁹ and from 0.194 × 10⁻⁶ to 118 × 10⁻⁶ m/s, respectively. The predicted moisture profiles showed adequate agreement with the experimental observations, with the average error between experimental and predicted results being ±13.7%.     

Modelling the mass transfer during convective, microwave and combined microwave-convective drying of solid slabs and cylinders

In the present work, the mass transfer characteristics, namely moisture diffusivity and moisture transfer coefficient, of slab and cylindrical potato samples were evaluated by adopting the analytical model proposed by Dincer and Dost [Drying Technology, 13,1/2 (1995), 425]. As part of the experimental work, the moisture contents of slab and cylindrical potato samples dried under convective, microwave and combined convective–microwave conditions (air temperature, 30–60 °C; air velocity, 1–2 ms⁻¹; microwave output power, 30–650 W) were measured. From the data collected the drying coefficients and lag factors were calculated and incorporated into the model. The results showed a reasonably good agreement between the values predicted from the correlation and the experimental observations; average error between experimental and predicted results less that 10%. The experimental system exhibited mass transfer Bi numbers in the range 0.038–11.4, thus indicating the presence of finite internal and external resistances. Moisture diffusivity values in the range 0.13×10⁻⁸ to 24.22×10⁻⁸ m²s⁻¹ were calculated.     

Calculation of the total lethality of conductive heat in cylindrical cans sterilization using linear and non linear survival kinetic models

There is growing evidence suggesting that inactivation of bacterial spores may follow the Weibullian model, of which the log linear relationship between survival ratio and time is just a special case. Where true, the time and not only the temperature dependence of the rate must be taken into account. Also, it is of interest to estimate spores survival not only at the coldest point but also throughout the whole container's volume.Numerical calculation on changing survival ratios was performed by combining the conductive heat transfer model with that of the nonlinear inactivation kinetics. Results are based on published linear and non linear inactivation parameters of Clostridium botulinum spores, typical thermal properties of solid foods and realistic thermal processing conditions. Results could be used to quantify the efficacy of thermal processes of solid products in terms of spores' residual survival ratio at the coldest point and in the container as a whole.