The purpose of this work was to study the effects of spray-drying conditions on the physicochemical characteristics of blackberry powder using a central composite rotatable design. Inlet air temperature (140-180°C) and maltodextrin concentration (5-25%) were employed as independent variables. Moisture content, hygroscopicity, anthocyanin retention, color, powder morphology, and particle size were analyzed. A higher inlet air temperature significantly increased the hygroscopicity of the powder, decreased its moisture content, and led to the formation of larger particles with smooth surfaces. Powders produced with higher maltodextrin concentrations were less hygroscopic, slightly lighter and less red, and had a lower moisture content. Anthocyanin retention was mainly affected by drying temperature due to the heat sensitivity of the pigment. The optimal processing conditions were an inlet air temperature of 140-150°C and maltodextrin concentration of 5-7%. Overall, these results indicate that good quality powders can be obtained by spray drying, with potential applications for the food industry.
A promising approach for the application of ultrasound to assist in convective food drying was developed and tested in this study. The application of ultrasound is based on the transmission of ultrasonic energy as a combination of airborne contacts and through a series of solid contacts between the ultrasound element and the product tray as the ultrasonic vibration transmitting surface. A computer-based ultrasonic drying setup was built to allow continuous recording of the process variables in real time and enabled simulation of dehydration to be accomplished under controlled conditions over a range of drying parameters. Apple slices were dried using the drying setup to study the influence of ultrasound in combination with conventional hot air drying on drying kinetics and product quality. The results from this work indicate that ultrasound can simultaneously be applied to accelerate the processing time (i.e., reduce energy consumption and increase production throughput) in conventional hot air drying without compromising product quality. It appears that the magnitude of influence of ultrasound to enhance the air-drying process depends on the process variables employed. In particular, the ability of ultrasound to improve the efficiency of the convective drying process appears to be maximized when using low temperature and high ultrasonic power level. This finding maybe very useful when there is a need to effectively dehydrate heat-sensitive products or when shorter drying times are required in order to achieve better retention of the functional and nutritional properties of the product.
The objective of this work was to evaluate the effect of the type of wall material and the oil load on the microencapsulation of flaxseed oil by spray drying. Gum arabic, whey protein concentrate, and a modified starch were used to produce the microcapsules, each with four oil concentrations (10, 20, 30, and 40% oil, w/w, with respect to total solids), for a total of 12 tests. Initially, the feed emulsions were characterized for stability, viscosity, and droplet size. Then they were dried in a laboratory-scale spray dryer and the resulting particles were analyzed for encapsulation efficiency, lipid oxidation, moisture content, and bulk density. The increase in oil concentration led to the production of emulsions with larger droplets and lower viscosity, which directly affected powder properties, resulting in lower encapsulation efficiency and higher lipid oxidation. Among the three wall materials evaluated, the modified starch showed the best performance, with the highest encapsulation efficiency and lowest peroxide values.
Increasing global energy demand and the application of more energy-consuming processes has forced food industries to investigate alternative processes. This article pertains to one such novel and promising alternative drying process called electrohydrodynamic (EHD) drying. EHD is a method of inducing electric wind that is generated by gaseous ions under the influence of a high-voltage electric field. This article evaluates the available literature and discusses the experimental investigations carried out to explain the effect of operating parameters on the drying rate and specific energy consumption (kJ/kg water) of the EHD process. Through the review it was established that the corona current increased linearly with an increase in applied voltage (kV) for both positive and negative polarities and a negative corona discharge produced a larger corona current compared to a positive corona discharge. It was also revealed that the specific energy consumption increased with an increase in applied voltage for both polarities but was lower compared to conventional drying processes such as fluidized bed drying; however, it was observed that the specific energy consumed by the EHD process was lower than that of latent heat of vaporization, indicating the removal of water from the surface of the sample by other means in addition to evaporation. Electrode configuration plays an important role in determining the efficiency of the EHD process; the multiple-needle electrode configurations had better efficiency than wire and single-electrode configurations. Recent and past studies on application of EHD both postharvest and in food processing were also reviewed and the benefit of using EHD for food and bioprocessing due to its unique properties supported the feasibility and applicability of EHD as a suitable alternative for processing thermally sensitive biological materials.
Purification of municipal wastewater generates huge amounts of sewage sludge, which contains large quantities of water, biomass, and extracellular polymeric substances. It is widely known that sewage sludge usually has a poor dewaterability. A large amount of water in sludge directly translates into high transport and handling costs; therefore, sludge treatment and disposal usually requires over 50% of the operation budget for wastewater treatment plants. The application of a low electric field through the sludge segment, called electro-dewatering, is considered to improve the liquid-solid separation, resulting in low water content in the sludge cake. However, prediction of dewatering enhancement for sewage sludge, in particular, offers a challenge due to variations in sludge pretreatment practices and the lack of harmonized testing methodologies. In this review article, the aspects that have an effect on sewage sludge electro-dewatering and its feasibility are discussed in the light of recent technological developments. It was found that electro-dewatering has several potential benefits, such as removal of pathogens, reduction in energy and transportation costs, and prevention of filter fouling.
The main aim of this work was to test the feasibility of power ultrasound to intensify low-temperature drying processes. For this purpose, the convective drying kinetics of carrot, eggplant, and apple cubes (side 10 mm) were carried out at atmospheric pressure, 2 m/s, −14°C, and 7% relative humidity with (acoustic power 19.5 kW/m 3 ) and without ultrasound application. Under the same experimental conditions, kinetics studies of ethanol removal from a solid matrix were also performed. Diffusion models were used to describe drying curves and identify kinetic parameters in order to evaluate and quantify the process intensification attained by ultrasound application. The effect of ultrasound application was similar for all products tested; that is, the drying time was shortened between 65 and 70%. In the case of ethanol removal, the time reduction achieved by ultrasound application was 55%. The mass transfer coefficient and effective moisture diffusivity increased by 96 to 170% and by 407 to 428%, respectively, when ultrasound was applied.
Advances in the study of the rate processes in spray drying have helped improve product quality. Single droplet drying (SDD) is an established method for monitoring the drying kinetics and morphological changes of an isolated droplet under a controlled drying environment, mimicking the droplet convective drying process in spray drying. To enhance particle quality requires understanding of both the particle formation process and knowledge of how different particle properties are affected by the drying conditions used. The latest development in the SDD technique enables evaluation of these aspects by incorporating a dissolution test in the drying experiment. The experiment is realized by attaching a solvent droplet to a dried/semi-dried single particle in situ and then video-recording the resultant morphological changes. Some of the particle (e.g., crystallinity) properties obtained under different drying conditions can be modelled using the measured droplet drying kinetics. This paper reviews the applications of SDD experiments in measuring the drying kinetics and monitoring the droplet morphological changes during drying. Some examples of extending the glass filament SDD technique to examine particle functionalities are discussed. SDD experiments are shown to be a powerful tool for particle engineering due to its ability to study both the external convective transport process of a single droplet and to understand the different particle functionalities of the resultant single dried particle.
Removal of moisture from biological materials, popularly called drying, has numerous benefits, including ease of handling due to reduction in bulk, resulting in reduced handling costs. Moreover, drying prevents microbial growth and spoilage. Though different drying techniques share a common objective, conceptually they are different and require modification/adaptation based on the biomaterial that is dried. There have been significant scientific advancements in the past century in the field of drying of foods, fibers, and fuel. This article will provide an extensive review of various drying pretreatments and different hybrid drying techniques, including supercritical and fluidized bed concepts, microwave drying, superheated steam drying, and heat pump drying to meet tomorrow's food and energy needs.
Diverse types of vegetable snacks made using different drying methods are becoming increasingly commercially important for the food processing industry worldwide because they are also recognized as healthy for human consumption. Here we consider four aspects of drying snacks: unit operations currently used in the industry, novel or emerging methods with nontraditional means, combined (or hybrid) drying methods, and the quality changes during storage. Each drying method has its own advantages and limitations. Hybrid drying techniques are being developed to maximize the benefits of different drying techniques to produce better quality vegetable snacks that are attractive to the consumer. The merits and limitations of more than 10 drying techniques used for making dried vegetable snacks are discussed. Moreover, several new vegetables snacks dried using new drying methods are presented and discussed. A comprehensive review of the recent progress in production of dried vegetable snacks is presented and recommendations are made for future research.
A new technique for lycopene microencapsulation by spray drying using dehumidified air as the drying medium was developed and the optimum operating conditions for encapsulation efficiency were determined. A pilot-scale spray dryer was employed for the spray-drying process. The modification made to the original design consisted of connecting the dryer inlet air intake to an absorption air dryer. The dextrose equivalent (DE) of maltodextrin, ratio of core to wall material, feed temperature, inlet air temperature, drying air flow rate, and compressed air flow rate were the factors investigated with respect to encapsulation efficiency. The resulting microcapsules were evaluated in terms of moisture content, bulk density, rehydration ability, lycopene isomerization, and storage stability. The optimum operating conditions were found to be as follows: ratio of core to wall material, 1:3.3; feed temperature, 52°C; inlet air temperature, 147°C. Under these conditions, the maximum encapsulation efficiency was about 93%. The use of dehumidified air was proven to be an effective way of increasing lycopene encapsulation efficiency.
Increasing globalization is driving agricultural production in developing countries toward better recovery levels and high additional value. A great opportunity is thus offered to emerging economies. By adopting appropriate and improved methods that allow better preservation, transport, and storage and that conform to the rigorous requirements and standards of organoleptic and nutritional quality as well as stringent hygienic criteria, emerging economies can derive significant benefits. Drying of biological materials usually results in shrinkage. The impact of shrinkage is often highly prejudicial for both the function and use of these materials. On the one hand, shrinkage results in a sharp decrease in water diffusivity through the porous structure (for dehydration and rehydration processes). On the other hand, the compact structure of dried biological material is usually unsuitable in terms of organoleptic quality and is inadequate for grinding. Thus, it is becoming very important to include retexturing and structure-expanding processes in standard drying processes. To this end, the instant controlled pressure drop (DIC) technology has been proposed and successfully tested as a texturing process for partially dried materials, which should normally intensify the whole operation. The quality of the final product as well as the performance of the drying process can also be dramatically improved. Finally, for a large category of dried fruits and vegetables, and even freeze-dried materials, microbiological contamination and the presence of insects and larvae are serious problems. DIC technology can be used as an ultra-high-temperature treatment for a controlled decontamination. Such dried, expanded, and completely decontaminated products can be used as highly nutritional snacks. They can easily be ground to produce expanded granulated powders with excellent sensory, nutritional, functional, and textural properties.
This article aims to study the mass transient diffusion in solids with a cylindrical shape. To this end, the one-dimensional diffusion equation was discretized using the finite volume method with a fully implicit formulation. The solution can be used to simulate diffusive processes and to determine thermophysical parameters via optimization techniques. The computational package developed was applied to study the thin-layer drying of peeled bananas. Three models were used to describe the drying process: (1) the volume V and the effective mass diffusivity D are considered constant; (2) variable V and constant D; (3) V and D are considered variable. For all models, the convective mass transfer coefficient h is considered constant. The statistical indicators show that for the two cases analyzed (low and high temperature), model 3 describes the drying process better than the other models.
Electrohydrodynamic (EHD) drying is a novel method of nonthermal drying. A corona discharge using multiple electrodes and a high-voltage electric field of 5.2 kV · cm −1 was produced to investigate the drying enhancement of carrot slices and its effect on color and shrinkage. The EHD setup consisted of 13 stainless steel needle points connected to a DC power supply and a stainless steel plate. EHD + drying, EHD − drying, oven drying at 55°C, and ambient air drying control at 25°C for 5 h resulted in 79.5, 77.7, 77, and 22.5% total moisture removal from the fresh carrot slices, respectively. The final shrinkage of the EHD ± drying was less than that of oven drying but was higher than that of ambient air drying. It was estimated that the energy consumption of oven drying was several times greater than those of EHD ± drying. The conventional drying processes changed all color parameters, whereas the color for EHD ± dried samples remained almost the same. The carrot slices' temperature during drying by EHD ± was significantly less than that of those dried by oven and ambient air drying.
A porous structure is an important characteristic of crisp food and can be produced by a puffing process. However, puffed products may brown during puffing. To limit the browning reaction, food, in particular fruits, needs to be osmotically treated before puffing. This research therefore studied how osmotic treatment affects the quality of a puffed fruit sample, viz. banana. Banana with 20-23° Brix total soluble solid was immersed in sucrose solution concentrations at 30, 35, and 40° Brix and dried at 90°C using hot air until the sample moisture content was reduced to 30% dry basis. Then the banana slices were puffed using superheated steam at 180, 200, and 220°C for 150 s and dried again at 90°C until the sample moisture content reached 4% (db). It was found that osmotic dehydration could improve the color of puffed banana, with less browning than the non-osmotically treated puffed banana because the amounts of glucose and fructose in banana, which serve as important reagents for browning reactions, were decreased. The puffing temperature and osmotic concentrations did not enhance the browning rate. Sucrose impregnation resulted in longer drying times and limited banana cell wall expansion due to the interaction between the hydroxyl group of sucrose and that of banana tissue. This interaction further resulted in significantly higher shrinkage of the osmotically treated sample and a denser structure as viewed by scanning electron microscopy. The morphology of osmotically treated banana was a hard and brittle texture.
The sensorial profile, nutritional quality, and rehydration properties of dried food depend on the structure of the dehydrated material. The molecular, supramolecular, micro-, and macrostructure is influenced by the applied drying conditions. During drying of foods, specific product structures can be generated. For instance, during drying at elevated temperatures, Maillard reactions are accelerated. Thus, peptides and reducing sugar molecules are transformed into taste-active molecules. During drying, proteins are also denatured, and their three-dimensional structure changes accordingly. Following this denaturing, proteins can coagulate. Furthermore, gelling of starch is observed during drying of food. In addition to these reactions, isomerization, oxidation, and various other reactions are accelerated during drying at higher temperatures. Thus, the molecular structure of food products changes significantly during most drying processes. Depending on the drying conditions, different supramolecular structures of solid food products are generated during dehydration of solutions. The drying velocity has a significant impact on the characteristics of the generated supramolecular structure. Fast dehydration of liquid products leads to amorphous structures, whereas slow drying allows substances with low molecular weight to crystallize. Furthermore, the chosen drying technology, solid content of the wet product, composition, pressure fluctuations during drying, and the kinetics of mass transfer influence the generation of microstructures. In addition, the liquids can be enriched with gas before drying in order to increase the product's porosity. Finally, the macrostructure and the optical appearance of the dry product are affected by the drying technology applied and the chosen drying conditions.
This article reports a study of the effects of the drying methods and drying carriers on system performance and physicochemical properties of spray- and spouted bed-dried phytopharmaceutical preparations from Bidens pilosa L. Colloidal silicon dioxide, β -cyclodextrin, maltodextrin dextrose equivalent (DE) 10, and microcrystalline cellulose were used as drying carriers. The dried product was characterized by the particle size and morphology, total flavonoid content, solubility, flowability, and water activity. High-performance liquid chromatography (HPLC) was used to detect four marker compounds previously reported for this plant. Spray and spouted bed drying systems were compared through energetic efficiency, product recovery, elutriation, and product accumulation. The crystalline state of the powders was assessed by X-ray diffraction. Results showed high degradation rates for total flavonoid content and marker compounds during spouted bed drying. Depending on the drying carrier added to extractive solutions, different degrees of protection from degradation were conferred, and the physical characteristics of the product were changed accordingly. The lowest flavonoid degradation (8.6%) and the higher concentration of marker compounds were obtained using β -cyclodextrin as the drying carrier. Particle size was higher when a blend of Aerosil (Evonik Degussa, Hanau, Germany) and cellulose was employed as the drying carrier. A maximum product recovery of 86.9% was achieved by spray drying and 72.9% by spouted bed drying with the Aerosil : cellulose composition.
Powders intended for the use in dry powder inhalers have to fulfill specific product properties, which must be closely controlled in order to ensure reproducible and efficient dosing. Spray drying is an ideal technique for the preparation of such powders for several reasons. The aim of this work was to investigate the influence of spray-drying process parameters on relevant product properties, namely, surface topography, size, breaking strength, and polymorphism of mannitol carrier particles intended for the use in dry powder inhalers. In order to address this question, a full-factorial design with four factors at two levels was used. The four factors were feed concentration (10 and 20% [w/w]), gas heater temperature (170 and 190°C), feed rate (10 and 20 L/h), and atomizer rotation speed (6,300 and 8,100 rpm). The liquid spray was carefully analyzed to better understand the dependence of the particle size of the final product on the former droplet size. High gas heater temperatures and low feed rates, corresponding to high outlet temperatures of the dryer (96-98°C), led to smoother particles with surfaces consisting of smaller crystals compared to those achieved at low outlet temperatures (74-75°C), due to lower gas heater temperatures and higher feed rates. A high solution concentration of the feed also resulted in the formation of comparably rougher surfaces than a low feed concentration. Spray-dried particles showed a volume-weighted mean particle size of 71.4-90.0 µm and narrow particle size distributions. The mean particle size was influenced by the atomizer rotation speed and feed concentration. Higher rotation speeds and lower feed concentrations resulted in smaller particles. Breaking strength of the dried particles was significantly influenced by gas heater temperature and feed rate. High gas heater temperatures increased the breaking strength, whereas high feed rates decreased it. No influence of the process parameters on the polymorphism was observed. All products were crystalline, consisting of at least 96.9% of mannitol crystal modification I.
Saffron is the most expensive spice and Iran is the largest producer of this crop in the world. Saffron quality is profoundly affected by the drying method. Recent research has shown that hybrid photovoltaic-thermal solar power systems are more efficient in comparison with individual photovoltaic and thermal systems. In addition, heat pump dryers are highly energy efficient. Furthermore, they are suitable for heat-sensitive crops such as saffron. Therefore, in the present study, the performance of a hybrid photovoltaic-thermal solar dryer equipped with a heat pump system was considered for saffron drying, in order to obtain a high-quality product and reduce fossil fuel consumption. The effect of air mass flow rate at three levels (0.008, 0.012, and 0.016 kg/s), drying air temperature at three levels (40, 50, and 60°C), and two different dryer modes (with and without the heat pump unit) on the operating parameters of the dryer was investigated. The results of the investigation showed that total drying time and energy consumption decreased as air flow rate and drying air temperature increased. Applying a heat pump with the dryer led to a reduction in the drying time and energy consumption and an increase in electrical efficiency of the solar collector. The average total energy consumption was reduced by 33% when the dryer was equipped with a heat pump. Maximum values for electrical and thermal efficiency of the solar collector were found to be 10.8 and 28%, respectively. A maximum dryer efficiency of 72% and maximum specific moisture extraction rate (SMER) of 1.16 were obtained at an air flow rate of 0.016 kg/s and air temperature of 60°C when using the heat pump.
Spray drying was applied for the production of Lactobacillus plantarum TISTR 2075 powder using maltodextrin as the carrier. A survival rate of 0.85% was achieved for this probiotic bacteria after spray drying. To improve the survival of this strain during the spray-drying process and storage, various protectants were added before drying. These included protein, trehalose, fibersol, ascorbic acid, isomalt, palatinose, and gum acacia. The results indicated that trehalose and protein (a combination of soy protein isolate and milk protein concentrate) significantly (P < 0.05) enhanced the viability during spray drying, with survival rates of 57.70 and 25.31%, respectively. Survival of the dried strain was also monitored over a period of 12 months' storage at 4 and 25°C. Higher temperature induced lower viability of the strain in all protectants during this long-term storage. Accelerated storage tests using temperatures of 37, 45, 60, and 80°C were also applied to the spray-dried powders. A temperature-dependent prediction model was developed to determine the viability of the spray-dried L. plantarum TISTR 2075 in different protectants for long-term storage.