Odilio Alves-Filho

Kinetics and Mass Transfer during Atmospheric Freeze Drying of Red Pepper

Drying is applied for moisture removal to allow safe and extended storage. Red pepper (Capsicum annum) samples were heat pump dried in fluidized bed at different air temperatures. A slightly modified solution of the diffusion equation was used to describe the kinetics and drying rates of red pepper. The model well described the low- and medium-temperature drying processes. The determined effective mass diffusivities varied from 0.7831 to 4.0201 × 10−9 m2/s and increased consistently with drying air temperature. The mass diffusivity was correlated to temperature by linear regression with coefficient of determination equal to 0.999 and negligible standard error.

Microwave Vacuum–Assisted Drying of Green Peas Using Heat Pump and Fluidized Bed: A Comparative Study Between Atmospheric Freeze Drying and Hot Air Convective Drying

This study investigates the performance of microwave vacuum–assisted drying (MVD) of green peas using both fluidized bed and heat pump systems. A comparative study of heat pump–fluidized bed atmospheric freeze drying (HP-FB-AFD) and heat pump–fluidized bed hot air convective drying (HP-FB-HACD) was conducted. The initial drying rates of green peas were 0.04 and 0.12 1/min for HP-FB-AFD and HP-FB-HACD, respectively. Moisture diffusivity of green peas dried in HP-FB-HACD and HP-FB-AFD were 1.04 × 10−9 and 6.94 × 10−11 m2/s, respectively. HP-FB-AFD did not entail changes in the starch granules and preserved the sample size and shape with minimal shrinkage (20%), whereas HP-FB-HACD generated significant volumetric shrinkage (50%). HP-FB-AFD+MVD created a desirable porous inner structure of the final product. HP-FB-HACD+MVD significantly increased the hardness of the dried product and produced green peas with a compact structure and tightly packed cells. Neither HP-FB-AFD+MVD nor HP-FB-HACD+MVD significantly influenced the color of dried green peas. To respond to the current demand for high-quality products, the multistage combined HP-FB-AFD+MVD method is an interesting technique for green peas processing.

Microwave-Assisted Atmospheric Freeze Drying of Green Peas: A Case Study

Atmospheric freeze drying (AFD) is based on the sublimation of ice due to a pressure gradient (convective drying), and is a dehydration process for temperature-sensitive products. Since the process is slow in general, microwave radiation (MW) was applied in order to increase the sublimation in fluid and fixed bed conditions at drying temperatures of −6°C, −3°C, and 0°C. The modified Weibull model was used to describe the drying behavior for all investigations. With 280 Watt power supplied to the magnetrons, it was possible to reduce drying time by approximately 50%. The drying efficiency was approximately 30%, while the SMER was increased by 0.1 to 0.3 kgwaterkWh−1, which gives better energy efficiency for the microwave drying system used in this investigation. The product quality (color reduction and particle size/porosity) was well preserved in fixed bed drying at −6°C and −3°C, while the product quality was reduced significantly in microwave AFD experiments at 0°C and in a fluid bed. The drying rates of AFD in a fluid bed condition were not as high as those in a fixed bed. MW-AFD in a fixed bed condition at temperatures of −6°C and −3°C performed best regarding product quality, drying time, and process control.

Microstructural Changes of Apples (Granny Smith) During Drying: Visual Microstructural Changes and Possible Explanation from Capillary Pressure Data

The relationship between water content and capillary pressure and the microstructural changes in apples (Granny Smith) during drying was studied. Apples were dried in a pilot tray dryer and samples, with different moisture contents, were put in liquid nitrogen. The remaining water was eliminated by the critical point method to avoid structural changes and samples were then observed by scanning electron microscopy (SEM). It was possible to characterize the internal space of the apples during drying and find a relationship between the drying rate and microstructural changes. We postulate that shrinkage during drying is mainly due to changes in capillary pressure.

Influence of Atmospheric Sublimation and Evaporation on the Heat Pump Fluid Bed Drying of Bovine Intestines

Experiments on atmospheric two-stage fluidized bed drying of bovine intestines with heat pump were carried out. The investigation covers innovative fluidized bed heat pump drying of bovine intestines. The two-stage drying consists of atmospheric moisture sublimation immediately followed by evaporation. Studies were done to establish the influence of the drying condition on the drying characteristics and product quality of bovine intestines and properties focusing on kinetics, diffusion, and color. The investigation of the drying characteristics has been conducted during moisture removal by evaporation and combined sublimation and evaporation. The effect of drying temperature on the drying constants was determined by fitting the experimental data using regression analysis techniques. The investigation revealed that the drying kinetics is most significantly affected by temperature. Correlations expressing the drying constants and effective moisture diffusivity dependence on the drying conditions are reported.

Heat Pump Drying Kinetics of Spanish Cheese

The manchego and mallorquin cheeses are produced under controlled conditions and long time is needed to develop unique texture and flavor. This traditional manufacturing method has challenges to be addressed by new technologies. Tests were performed to verify feasibility of application of heat pump technology for cheese drying and ripening. The measured kinetic data was fitted by three models to quantify moisture removal rates. Analysis revealed that this modern technology fits well this application and that it promoted similar or higher removal rates than traditional methods. Moreover, the highly efficient heat pump thermodynamic cycle leads to added benefits related to energy, costs and environment.