Marek Markowski

Drying Behavior of Carrots Dried in a Spout–Fluidized Bed Dryer

The effect of water blanching treatment and the inlet air temperature on drying kinetics as well as the quality attributes of carrot cubes dried in a spout–fluidized bed dryer at 60, 70, 80, and 90°C were analyzed. The material shrinkage and the rehydration potential were calculated to assess the changes in quality of dried carrots. It was found that the value of the air velocity during the drying of carrot cubes in a spout–fluidized bed dryer should be related to the moisture content of the carrot particles. A high value of air velocity at the beginning of the drying cycle and a lower value for the later stages were also required. The linear equation was correlated to the data of shrinkage of raw and blanched carrots. Blanching significantly influenced the coefficients in the shrinkage model derived for drying of carrot cubes in a spout–fluidized bed dryer, while drying temperature did not influence the shrinkage of carrot particles. The intensity of heat and mass transfer during spout–fluidized drying of carrot cubes was dependent on the drying temperature. A correlation was developed to calculate the values of effective moisture diffusivity of dried carrot cubes as a function of the moisture content and temperature of the material. It was observed that for any given time of rehydration, both the moisture content and the rehydration ratio calculated for samples dried at 60°C were higher than for samples dried at temperatures of 60, 70, 80, and 90°C.

Rehydration Behavior of Vacuum-Microwave-Dried Potato Cubes

Rehydration properties and microstructure of vacuum-microwave and hot air–dried potato cubes were examined. Two kinds of models were considered to describe the hydration kinetics: a diffusion model for a cube and two empirical equations, Peleg and Weibull. The values of the effective moisture diffusivity of soaked potatoes were in the range 1.17 × 10−9 to 4.73 × 10−9 m2/s. The vacuum-microwave drying technique resulted in puffed potato particles characterized by porous microstructure with a network of open cavities and the hot air drying gave the potato particles containing compacted cells with the low amount of open micro-caves. Higher rehydration ability was observed for the samples dried with microwaves under low pressure. Vacuum-microwave drying at 6 kPa seems to be the optimal drying condition for potato cubes, ensuring porous microstructure of dried material and low shrinkage of dried potato particles as well as their high recovery properties and rehydration.

Color Characteristics of Carrots: Effect of Drying and Rehydration

The aim of this study was to observe a change in color and a degradation of total carotenoids and β-carotene in carrots subjected to spout-fluidized bed drying at 60, 70, 80, and 90°C. Additionally, the color of carrots rehydrated at 95°C (10 min) was measured in order to estimate the reversibility of color changes caused by drying. Significant changes in a*, b*, ΔE*, and ΔC* were observed during drying and rehydration of carrots. The total difference in color and saturation ranged from 23.67 to 30.28, and from 22.97 to 29.90, depending on drying air temperature. The rate of deterioration of total carotenoids and β-carotene content influenced the color parameters of carrots. The first-order kinetic model adequately described evolution of a*, b*, ΔE*, and ΔC* derived for carrots during drying at 60, 70, 80, and 90°C. It was found that the spout-fluidized bed drying followed by rehydration changed the color of carrots irreversibly.

Drying Characteristics of Barley Grain Dried in a Spouted-Bed and Combined IR-Convection Dryers

A study was performed to determine the drying characteristics and quality of barley grain dried in a laboratory scale spouted-bed dryer at 30, 35, 40, and 45°C and an inlet air velocity of 23 m/s−1, and in an IR-convection dryer under an infrared radiation intensity of 0.048, 0.061, 0.073, and 0.107 W cm−2 at an air velocity of 0.5 m/s−1. The results show that the first, relatively short, phase of a sharp decrease in the drying rate was followed by the phase of a slow decrease. The time of barley drying depended on temperature of inlet air in a spouted-bed dryer and on radiation intensities in an IR-convection dryer. Barley drying at 45°C in a spouted-bed dryer was accompanied by the lowest total energy consumption. The average specific energy consumption was lower and the average efficiency of drying was higher for drying in a spouted-bed dryer. The effective diffusivities were in the range 2.20–4.52 × 10−11 m2 s−1 and 3.04–4.79 × 10−11 m2/s−1 for barley dried in a spouted-bed and in an IR-convection dryer, respectively. There were no significant differences in kernel germination energy and capacity between the two drying methods tested.

Effect of Variety on Drying Characteristics and Selected Quality Attributes of Dried Carrots

The effects of variety on drying characteristics, color, and water absorption of carrots were investigated. Six different varieties of carrots, viz. Kazan, Maxima, Nandor, Nektarina, Simba, and Tito were evaluated. The hot air drying characteristics of carrot cubes dried under forced convection conditions were determined and drying data were analyzed to obtain parameters of Page and first-order kinetic models as well as moisture diffusivity. Color characteristics were determined for fresh, dried, and dehydrated samples by measuring lightness (L*), redness (a*), and yellowness (b*). Water absorption data were analyzed for ground samples. It was observed that drying characteristics, such as color and water absorption were significantly influenced by variety. The varieties of Kazan and Nektarina were found to be characterized by highest and lowest moisture diffusivity of 7.52 × 10−9 and 3.31 × 10−9m2/s respectively. Kazan variety was also characterized by shortest drying time. The lowest changes in color caused by drying were observed for Tito variety. The variety of Kazan was characterized by the highest resistances to color changes affected by drying followed by rehydration. Nandor and Tito varieties displayed the highest water absorption near to 560 g/100 g. The best drying characteristics and good water absorption accompanied by the high color attributes of dried and rehydrated samples implies that Kazan variety is expected to be the most useful to drying industry.

Mass Transfer in the Celery Slice: Effects of Temperature, Moisture Content, and Density on Water Diffusivity

Abstract Statistical tests were applied to determine the effects of temperature, moisture content, density, and porosity of material on the effective moisture diffusion coefficient during convective drying of root celery. In biological materials with colloidal capillary-porous structure (like root celery), which shrink considerably during drying and show high heterogeneity, the effective water diffusion coefficient depends not only on material temperature and moisture content, but also on its density. It was found that statistical tests can be applied to predict which independent variables should describe the water diffusivity in colloidal capillary-porous materials. A mathematical model of the effective water diffusion coefficient in root celery was formulated as Arhenius-type equation with moisture content of the raw material, its temperature and density as independent variables.

Superheated Steam Drying of Distillers' Spent Grains on a Single Inert Particle

The article presents the results of drying a distillers’ spent grain fraction (DSG) of a stillage in superheated steam (SS). The study aimed at determination of the effect of SS parameters on drying kinetics of DSG deposited as a pasty layer on the 50-mm solid Teflon sphere. Drying was conducted at approximately 2 to 4 kPa above the atmospheric pressure, with steam temperature ranging from 110 to 160°C and steam velocity of 1 m/s. Samples were dried with SS at different processing times ranging from 60 to 360 min, depending on the SS temperature. During the initial warmup period of SS processing, the pasty DSG gained moisture due to steam condensation on its surface, which further evaporated at constant material temperature (apparent constant rate period). That period ended as soon as the condensate evaporated and temperature of the product passed the saturation point of steam. Only the falling drying rate period was observed. The drying rates increased from 0.02 to 0.83 L/min with the increase in steam temperature from 110 to 160°C, respectively. The effective diffusivity of moisture in DSG increased with the increase in steam temperature according to the Arrhenius-type relationship. The values of the effective diffusivity ranged between 3.24 × 10−10 and 2.48 × 10−9 m2/s, with the activation energy of 53.74 kJ/mol.

The influence of microwave-assisted drying techniques on the rehydration behavior of blueberries (Vaccinium corymbosum L.)

The aim of this study was to determine the effect of: (a) different drying methods, (b) hot air temperature in a convection oven, and (c) the moisture content of fruits dehydrated by multi-stage drying which involves a transition between different stages of drying, on the rehydration kinetics of dry blueberries. Models describing rehydration kinetics were also studied. Blueberries dehydrated by multi-stage microwave-assisted drying, which involved a hot air pre-drying step at 80 °C until the achievement of a moisture content of 1.95 kg H2O kg(-1)DM, were characterized by significantly higher rates of initial and successive rehydration as well as smaller initial loss of soluble solids in comparison with the samples dried by other methods. The highest initial rehydration rate and the smallest loss of soluble solids after 30 min of soaking were determined at 0.46 min(-1) and 0.29 kg DM kg(-1)DM, respectively. The Peleg model and the first-order-kinetic model fit the experimental data well.

Rheological Behavior of Hot-Air-Puffed Amaranth Seeds

Force-deformation and force-relaxation experiments were performed on amaranth seeds puffed at 290, 330 and 370°C. Less force and energy was required to cause a given deformation in seeds processed at 290°C than in those puffed at 330 and 370°C. It was also observed that the forces and energies required to produce a given deformation did not differ significantly (p ≤ 0.05) for seeds puffed at 330 and 370°C. The three-element generalized Maxwell model and Peleg model were applied for modeling force relaxation of puffed amaranth seeds. It was found that the generalized Maxwell model predicted the experimental data better than the Peleg model. The elastic parameters and asymptotic residual force of the generalized Maxwell model were significantly affected by puffing temperature, showing an increase with its rise. Relaxation times were not significantly affected by the puffing temperature. It was concluded that a higher puffing temperature resulted in a more rigid material and less viscous behavior.

SELECTED GEOMETRIC AND MECHANICAL PROPERTIES OF BARLEY (Hordeum Vulgare L.) GRAIN

The properties of grain of Mauritia and Prestige barley varieties were determined for moisture content of 12.5 and 15.5% wet basis. Broad variations were observed in the relationship between the moisture content of grain, its variety, and the geometric properties of barley. Most of the geometric properties of barley were dependent on both the cultivar studied and the moisture content of grain, while selected characteristics were dependent on moisture content of grain or barley cultivar only. The values of displacement, force and energy required for kernel rapture were lower for Mauritia variety than Prestige variety and were not dependent on the moisture content of grain.