Search

Feasible utilization of superheated steam spray drying at different inlet temperatures (160–200 °C) and feed rates (3–15 mL/min) to produce instant coffee and sodium copper chlorophyllin (natural green colorant) powders was assessed. Yield, physical properties and morphology of the steam-dried powder were determined and compared with those of the air-dried one. Superheated steam spray drying might not be a proper method for producing coffee powder as at all test conditions coffee extract adhered and dried on the wall of the chamber. Superheated steam spray drying, on the other hand, has the potential to produce the color powder with smaller particle size, higher bulk density and more wrinkle surfaces, resulting in the superior solubility. Mean diameter (D[4,3]), bulk density and solubility time of the steam-dried powder were 15.53–15.97 µm, 0.67–0.68 g/cm3 and 192–226 s, while those of the air-dried powder were 29.03–31.02 µm, 0.34–0.35 g/cm3 and 244–283 s, respectively. In terms of yield and color, both of the powders and of the reconstituted solutions, no significant differences among the air-dried and steam-dried powders were observed. [ABSTRACT FROM AUTHOR]

The incorporation of red raspberries in bakery and dairy products is limited due to the fragility of the berries. This compromises the appearance of the food product due to the bleeding of juice caused by tissue rupture. In this study, we developed vacuum-impregnated dehydrofrozen red raspberries from fresh fruit. Initially, we optimized drying and freezing conditions for red raspberries that were not vacuum impregnated using air drying alone and in combination with osmotic dehydration, followed by air blasting and cryogenic freezing methods. Later, optimal conditions of partial drying and freezing were used for raspberries that were vacuum impregnated with low methoxyl pectin (LMP) at 10 g of pectin kg−1 of solution and calcium chloride (CaCl2 · 2H2O) at 30 g of calcium kg−1 of pectin. Conditions for the vacuum impregnation of raspberries were based on our previous research. The berries were partially dehydrated using hot air (65 °C) until a final water content of 0.65 g of water g−1 of fruit was reached. Next, the berries were placed in glass jars, sealed, and cooled at 4 °C for 2 h. They were then frozen by air blasting and stored for 2 months at −35 °C prior to evaluation. The mechanical properties of the berries, including the maximum force (FM) and gradient (GC), were considered to be suitable indicators of fruit firmness. Results demonstrate that raspberries impregnated with pectin and calcium and then partially dried and frozen have higher FM and GC values than commercially frozen-thawed berries. These dehydrofrozen raspberries show improved structural integrity for use in bakery and dairy products. [ABSTRACT FROM AUTHOR]

The purpose of this research was to develop an approach for porosity estimation in the process of convective air drying. Fresh apple slices were exposed to 80°C drying to equilibrium moisture content 0.2 g/g. Porosity at different stages of drying was estimated using three approaches: (1) direct volume and mass measurements, (2) pycnometer measurements, and (3) theoretical model. All three approaches were in good agreement in the range of moisture contents above 1.0 g/g. However, at moisture contents below 0.26 g/g, significant deviation of pycnometer measurements from both experimental estimates and theoretical model was observed. This difference could be explained by transformation of open pores into closed pores due to glass transition phenomenon. This study presents an example of separate quantitative estimation of total, open-, and closed-pore porosity. [ABSTRACT FROM PUBLISHER]

This article presents a study of the effect of drying methods on dyeing capacity of widespread European flora dyestuff plant materials. The natural colorants, derived from the selected plant materials, were applied on chemical pulp in order to examine their dyeability. In this work, three different drying methods were examined—the natural, the air-, and the freeze-drying method—in various conditions. The plant materials that were dried naturally show weak dyeing results in comparison with the air- and freeze-dried materials. Freeze drying significantly improved the dyeing capacity of dyestuff plant materials with high initial moisture content. On the other hand, air drying at low temperature and high relative humidity improved the dyeing capacity of plant materials with low initial moisture content. [ABSTRACT FROM AUTHOR]

Drying experiments on kelp (seaweed species) were conducted using air drying (AD) and infrared radiation drying (IRD) at different emission peak wavelengths of 2.4, 3.0, 5.0, and 6.0 µm. Temperature characteristics of the dried kelp were determined in terms of temperature distribution and surface–interior temperature variation. Rehydrated ratio, color, and texture before and after rehydration were measured to evaluate the quality of dried kelp products. Dielectric properties were also studied to observe the characteristics of rehydrated dried products. The results indicated that the total drying time required for IRD products was approximately 120 min, reduced by 56% compared to AD (275 min). Infrared-dried products at 2.4 μm wavelength and AD products were found to be more uniform from the thermal images and had higher rehydration ratios compared to others. IR-2.4 rehydrated products were the closest to blanched samples in hardness, springiness, cohesiveness, and chewiness. This research work concluded that infrared radiation drying has potential to be used for drying of kelp. [ABSTRACT FROM AUTHOR]

Low-temperature geothermal waters can be used efficiently in drying various vegetables and fruits, replacing sun-drying or drying using conventional fuels. A “geothermal” tomato dehydration plant has been operating since 2001 in Neo Erasmio, northern Greece, producing high-quality, “sun-dried” tomatoes. The unit uses low-cost geothermal water to heat atmospheric air to 56–58°C, which is introduced in a specially designed tunnel-type dryer. The scope of this work is to model the aforementioned tomato-drying process that uses low-enthalpy geothermal energy. The modelling procedure consists of two stages: the first stage focuses on the modelling of a single tomato piece, whereas the second stage is concerned with the modelling of air drying of tomatoes in a tunnel with trays moving in batches. The influence of air velocity, air temperature, and tomato tray loading on the drying process was investigated. The effect of flow configuration, i.e., co-current or counter-current operation, on the drying characteristics was also explored. The model can be used for the design and optimization of the continuous drying process existing in Neo Erasmio and can be easily extended and modified to deal with other agricultural products and tunnel designs. [ABSTRACT FROM AUTHOR]

To monitor the air-drying time of dimensional lumber, load beams equipped with a data logger were used to collect lumber weight loss data. A weather station on the same site as the air-drying experiment was used to obtain the information regarding air temperature and relative humidity and wind velocity. A multiple regression model for estimating the drying rates for 2-in. × 4-in. × 8-ft (38.5-mm × 90-mm × 250-cm) green spruce/pine dimensional lumber was developed. Data analysis revealed that wind direction did not have a significant effect on the rate of moisture loss. Thus, the resulting regression equation takes temperature, relative humidity, initial moisture content, and wind speed into account. Based on historical weather information for a particular location, the model developed can be used as a practical guideline for estimating air drying time and therefore offers the user a valuable tool for planning green yard inventory. [ABSTRACT FROM PUBLISHER]

In this study, green pea drying is investigated experimentally in a laboratory-scale spouted bed dryer. A mathematical model is also developed to investigate the effect of operating conditions on the performance of the system. The effect of operating parameters such as inlet air temperature, particle size, and flow rate of the drying air on the performance of the dryer are studied experimentally. In order to build the process model, it is necessary to analyze the transport in both solid and gas phases. A complete set of equations with no adjustable parameters is derived for existing zones in the spouted bed dryer in order to predict variations in the temperature and moisture content of the solid and gas phases with time for batch drying conditions. Model results are compared with corresponding experimental data. Agreement between the model results and experimental data is good. [ABSTRACT FROM AUTHOR]

The present work evaluates the effect of different drying treatments on the textural attributes of bell peppers (green and red) and of pumpkins (C. maxima and C. moschata), which were dried using different methods: freeze-drying and air drying at different temperatures. From the results obtained it is possible to conclude that with respect to pumpkin no dependence was found between the fiber orientation and the hardness of the fresh vegetable, but a significant dependence was observed on the location of the sample, with those samples situated closer to the skin showing higher values of hardness. As to the bell peppers, the hardness is higher for those measurements made from the external side when compared to those made from the internal side. As to the effect of drying on the texture of the vegetables, it was found that the increase in air drying temperature drastically reduces the hardness of all vegetables and that freeze drying has an intermediate effect between the vegetables dried at 30°C and 70°C. Moreover, the springiness tends to be higher in dried bell peppers but no significant effect was observed on this attribute in the case of pumpkins. With respect to cohesiveness, the results are similar to those for springiness, so that it is slightly higher in the dried bell peppers, but in the case of pumpkins no differences were found. Finally, the trends observed for chewiness follow those for hardness in all cases at study. [ABSTRACT FROM AUTHOR]

In this study, a drying kinetics model for predicting the drying of green pea particles using a bench-scale spouted bed with heat carriers is investigated. The experiments were carried out under different operating conditions. The effect of inert particle diameter, inert particle type, and the mass ratio of inert particles to green peas was examined based on the performance of the dryer and the rate of drying. As expected, the rate of drying increased with increased mass ratio of inert particles to green peas and thermal diffusivity of inert particles. [ABSTRACT FROM AUTHOR]

In this study the effect of osmotic dehydration (OD) on the air-drying kinetics of chayote (Sechium edule (Jacq.) Swartz) fruits was investigated. Fresh and osmotically dehydrated chayote parallelepipeds (1 × 1 × 2 and 4 × 4 × 2 cm) were subjected to convective drying at air temperatures of 50 and 60°C, with air velocities of 1.5 and 2.5 m/s. The OD pretreatments were performed in 10 and 25% NaCl solutions (w/w) at 25°C during 3 h using a solution-to-fruit mass ratio of 4:1. The use of higher air velocities notably accelerated drying rates as manifested through significantly higher drying rate constants estimated with Page's model, whereas no effect of temperature was observed. A previously reported analytical solution that considers both product shrinkage and variable diffusivity was generalized to describe the drying kinetics of food products with parallelepiped geometry. Selected drying experiments were then fitted to this solution using six different sets of model assumptions. Results indicated that product shrinkage is the main factor to be considered in order to estimate reliable values for diffusion coefficients. The OD pretreatments produced a significant reduction of the initial moisture content of chayote slabs before drying, thus allowing shorter drying time, which may lead to reduced energy consumption. [ABSTRACT FROM AUTHOR]

Collard leaves (Brassica oleracea L. var. acephala) with an initial moisture content of 6.65 on percentage dry basis (%db) were dried by three different drying methods: microwave, air, and vacuum. Samples of fresh leaves, 25 g each, were dried until their moisture was down to 0.1 on a dry basis. The following drying levels were used in each of the drying processes: 350, 500, 650, 750, 850, and 1000 W for microwave drying; 50, 75, 100, 125, 150, and 175°C for air drying; and 0.4, 50, and 100 mmHg at 50 and 75°C for vacuum drying, respectively. Drying times ranged between 2.5 to 7.5 min, 8 to 210 min, and 35 to 195 min for microwave, air, and vacuum drying, respectively. The data obtained compared well with a thin-layer drying model. Microwave drying at 750 W provided optimal results with respect to drying time, color, and ascorbic acid content (vitamin C). [ABSTRACT FROM AUTHOR]

Drying kinetics of garlic cloves was investigated by drying 5 mm thick slices in air, vacuum, and nitrogen atmosphere. The drying coefficient and lag factor were estimated from the slope and intercept of the moisture ratio time plot based on a model by Dincer-Hussain. Both drying coefficient and lag factor increased with increasing drying temperature. The diffusivity estimated from the Fick's law of diffusion and Dincer-Hussain's model differed, because Fick's law assumes negligible external mass transfer, whereas Dincer-Hussain's model considers both internal and external mass transfer resistance. Allicin, which is rapidly produced by the action of alliinase on alliin when fresh tissue is crushed, is the main biologically active phytochemical of garlic. Air drying at 50°C, vacuum drying at 50 and 60°C, nitrogen atmosphere drying at 40°C gave lowest losses of allicin potential. In general, the loss of allicin potential increased with increasing drying temperature, and drying below 50°C should be the best drying condition for the retention of allicin potential. This could be due to higher retention of alliinase activity during lower temperature drying. The loss of allicin potential decreased with the increase of slice thickness. This may be explained by lower structural damage and by lower shrinkage in the case of thicker slices. [ABSTRACT FROM AUTHOR]

To develop a highly efficient drying technique for sea cucumber, the effects of different drying methods on the drying procedure and product quality were investigated. FD could lead to the best quality but took the longest time, and AD product quality was too poor. VMD was introduced to combine with FD to get acceptable quality and reduce drying time. In order to get optimal technique parameters, an RSA experiment was carried out. The optimal technique parameters of combination drying of FD-VMD were 45% conversion point, 20-30 kPa chamber pressure, and 350-450 W microwave power. Compared with Freeze Drying (FD), Air Drying (AD)-Vacuum Microwave Drying (VMD) could reduce the drying time to half and maintain good product quality. [ABSTRACT FROM AUTHOR]

Cabbage samples were processed by air drying, vacuum drying, and freeze drying and then micronized to various particle sizes. It was observed that the drying method used has a significant effect on vitamin C content, color retention, and bulk density of the dried product. Freeze-dried product had higher vitamin C, good color retention, and better retained shape. [ABSTRACT FROM AUTHOR]

Carrot slices were subjected to the following four different pretreatments prior to vacuum frying: (1) blanching, (2) blanching and air drying, (3) blanching and osmotic dehydration, (4) blanching, osmotic dehydration, followed by freezing. The effects of these pretreatments on the physicochemical properties and fat distribution in vacuum-fried carrot chips were also investigated. There were significant differences in the total yield, amounts of carotenes, vitamin C, and the color values of carrot chips following different pretreatments (P < 0.05). Pretreatment significantly affected the water content, fat content, and water activity of carrot chips (P < 0.05), while there were no significant differences in the breaking force of carrot chips treated with different pretreatments (P > 0.05). Spearman correlation analysis showed a high positive correlation between the fat content of carrot chips and the initial water content of carrot slices. The fat distribution pattern depended on the initial water content and the structure of the material left by water evaporation. [ABSTRACT FROM AUTHOR]

Air drying of camu-camu slices was performed in order to estimate the effect of air temperature on the kinetics of ascorbic acid thermal degradation. Moisture variation during the air drying process was monitored gravimetrically by weighing the trays at predetermined time intervals. The experimental points were adjusted by Fick's diffusion model and by the Page empirical model. The effective diffusion coefficient (D eff ) ranged from 8.48 × 10 -10 to 1.34 × 10 -9 m 2 /s.The ascorbic acid content was evaluated in samples taken during the drying process using Iodine titration, and the results modeled by the Weibull equation. Concerning ascorbic acid retention the best drying condition required air at 50°C. The ascorbic acid retention was 78%, when the moisture content of the product reached 10% (wet basis). [ABSTRACT FROM AUTHOR]

The drying rates in moving bed dryers are compared. The gas and the solids to be dried are in parallel flow or counterflow. A new simplified method to simulate the drying in parallel and counterflow moving beds is developed. This model is based on the solution of arbitrary experimental or theoretical drying rate Equations of single solid particles (or thin-layer drying rate equation) coupled with heat and mass conservation Equations of the dryer. The solution is presented in an integral form of the drying equation showing the relation between time or location in the dryer and degree of drying. The method allows rapid calculation of the moisture, vapor mass fraction, and temperature distributions along the dryer in drying with moist air or steam. The model is demonstrated by using a result based on the receding front evaporation model as the specific thin-layer drying equation in the moving bed model. Wood chips are chosen as an example of the substance to be dried, but the method applies also for other medium, if the dependence of the drying rate on moisture and ambient temperature and humidity (thin layer drying rate) is known. The size of the dryer needed to reach the same degree of drying operating in the parallel mode is much greater than that of counterflow type, when the drying medium is air or flue gases. The reason for the poorer drying in parallel flow is mainly the unfavorable distribution of the evaporation temperature. In steam drying, the difference in the size is not so great, since the evaporation takes place approximately at constant temperature. [ABSTRACT FROM AUTHOR]

In this study, a modified Biot number analysis of hot air drying of small objects has been described. The derivations outlined in this article provide a platform for testing a number of assumptions made for the simple models. In particular, the uniform temperature assumption is focused upon. A number of calculation examples arc given based on previous experimental results. It is expected that the new calculation procedures can provide a better justification for the assumptions made in modeling air drying. [ABSTRACT FROM AUTHOR]

This study reports on finish drying of osmotically pretreated (dehydrated and sugar-infused) cranberries. The halved fresh berries pretreated in a standard osmotic solution (67.5 Brix at 50°C for 5h) were then freeze-dried, vacuum-dried and airdried in various dryers (cabinet-air-through, fluid bed, pulsed fluid bed, and vibrated fluid bed dryers) in order to identify the best drying technology. Energy consumption and product quality were chosen as the comparison criteria. The best product quality, quantified by the anthocyanins content, rehydration ratio, color and taste, was noted for freeze-dried berries. As all other drying methods gave similar, albeit slightly lower quality products than freeze-drying, the selection of a drying method could be based on the unit heat consumption. The vibrated fluid bed and the pulsed fluid bed should be favored because of the highest energy efficiency. Even though sugar infused into cranberries during osmotic pretreatment reduces drying rates during the second drying period as compared to untreated berries, osmotic dehydration reduces the total energy consumption on top of the preferential sensory characteristics of the final product. [ABSTRACT FROM AUTHOR]

Two-stage drying kinetics of cylindrical pieces of apples were evaluated by subjecting test samples first to various osmotic treatments and then to convective air drying to complete the drying process. Osmotic drying was carried out with cut apple cylinders of three different sizes (12, 17 and 20mm diameter), all with a length to diameter ratio of 1: 1, in a well agitated large tank containing the osmotic solution at the desired temperature. Solution to fruit volume ratio was kept greater than 60. After the osmotic treatment, apple slices were further dried in a cabinet drier at an average temperature 58°C. A central composite rotatable design (CCRD) with five levels of sucrose concentrations (34-63°Brix) and five temperatures (34-66°C) was used for osmotic treatment. Half-drying time and solids gain time were used as measures of rate of drying and associated diffusion coefficients for moisture loss and solids gain were evaluated. Half-drying time decreased with an increase in temperature or concentration, or a decrease in sample size. Diffusion coefficients were lower for smaller samples, and were higher for migration of moisture as compared to solids. For a given level of moisture removal, air drying times were shorter than osmotic drying times. Composite models were developed to describe the effect of process variables and particle size on the drying behavior of apple slices. [ABSTRACT FROM AUTHOR]

This paper presents an economic model for analyzing the cost behavior of dehumidifier timber drying process. Various costs, including those of air drying, are identified and quantified. Reasonable assumptions are made to simplify the calculation process. For species of both softwoods and hardwoods, the optimum air drying strategies are investigated based on two scenarios of existing commercial dehumidifier dryers and well-run high performance dehumidifier dryers. This paper finds that when the timber maximum air drying degrade rate is less than 5%, air drying adds significant value to the operation of dehumidifier dryers. This benefit accelerates with the extent of air drying. With the use of high performance dehumidifier dryers, the importance of air drying tends to decrease. The cost of air drying is very sensitive to both the assumed interest rate and timber maximum air drying degrade rate. [ABSTRACT FROM AUTHOR]