Laboratory-scale Spray Dryer Research Articles

The use of a plug-flow model for scaling-up of spray drying bioactive orange peel extracts

Abstract The spray drying of orange peel extracts was scaled up from a laboratory-scale spray dryer to a pilot-scale spray dryer using two methods to predict the parameters of the spray-drying process. The mass and energy balance model predicted the outlet gas temperature, absolute humidity and the final moisture content of the particles with 5%, 2% and 74% errors, respectively whereas, the plug-flow model successfully predicted these parameters with Industrial relevance Peels and seeds of citrus fruits, such as oranges, contain bioactive phenolic compounds that have demonstrated cancer-inhibition properties. However, due to their bitterness, they are not consumed and are considered to be waste material. The compounds can be extracted and turned into concentrated powder supplements. In powder form, these compounds can be easily incorporated in controlled and concentrated dosages into food formulae in order to create functional foods while masking the unpleasant taste. However, due to the heat sensitivity of these compounds, the minimum amount of heat treatment is required in the process. Spray drying, which is one of the fastest drying techniques available, can be used to convert these extracts into powders. However, spray drying these extracts is very challenging due to the presence of large amounts of sugars that cause stickiness and product loss during the process. In general, adding significant amounts of carriers to sugar-rich foods to overcome their stickiness during spray drying has been used in industry, compromising the purity of the final products. Moreover, in order to mass produce the powders, the process needs to be scaled-up. However, spray drying is extremely difficult to scale up using dimensional analysis (Oakley, 1994; Zlokarnik, 2003b). Computational fluid dynamic (CFD) simulations have been suggested as a powerful tool in this scale up of spray drying, but they are very time consuming. Therefore, if simpler models that do not require CFD simulations can adequately predict the process parameters, they can be used as fast estimation techniques for scale up. The results from this study guide the use of a plug-flow model for scaling up the process of spray drying orange-peel extracts while keeping an acceptable quality for the final product.

Spray drying bioactive orange-peel extracts produced by Soxhlet extraction: Use of WPI, antioxidant activity and moisture sorption isotherms

Spray drying of orange peel extracts was performed using a laboratory-scale spray dryer in order to assess the best operating conditions to be used in a subsequent scale-up process. Addition of whey protein isolate (WPI) to the liquid feed enhanced the yield of the process significantly from 30 ± 10% to 63 ± 3%. The moisture sorption isotherms of the powders were also determined at 30 °C, 40 °C and 50 °C and fitted by the Guggenheim-Andersen-de Boer (GAB) equation. The average net isosteric heat of sorption for the powders was determined using the Clausius–Clapeyron equation to be 70.5 kJ/kg. The total phenolic content (TPC) and the free radical scavenging capacity (SC50) of the powders were retained by 95 ± 5% and 95 ± 15%, respectively, during small-scale spray drying at an inlet air temperature of 150 °C and a corresponding outlet temperature of 70 ± 3 °C. Therefore, the best operating conditions for scale-up were suggested to be an inlet air temperature of 150 °C, a maximum allowable outlet temperature of 80 °C and a maximum allowable relative humidity for the exhaust air of 15%, while using a liquid feed containing 7.5% (w/w), dry basis WPI.

Investigation of suitable spray drying conditions for sugarcane juice powder production with an energy consumption study

Sugarcane juice was spray-dried under various conditions to determine the most suitable drying conditions for the manufacture of sugarcane juice powder. Initially, fresh, 30°Brix and 50°Brix sugarcane juice samples were dried in a laboratory-scale spray dryer at an air-drying temperature between 130 °C and 170 °C using maltodextrin, Arabic gum and dietary fiber as drying aids. It appeared that sugarcane juice should be concentrated under vacuum to 30°Brix and added with at least 15% maltodextrin before drying at 170 °C in order to obtain dried powder product with a low drying cost. After conducting the experiments in the laboratory, sugarcane juice powders were produced in a factory using an industrial-scale spray dryer under five drying conditions. It was found that the energy cost of industrial-scale production of sugarcane juice powder ranged between 0.77 USD and 2.06 USD per kg of powder. According to the results of the industrial-scale experiments, the sugarcane juice powder should be produced using vacuum evaporation of the sugarcane juice to 30°Brix prior to adding maltodextrin at 30% by weight and then spray drying at 190 °C.

Roles of particle size on physical and mechanical properties of dairy model solids

Lactose/milk protein isolate (MPI) solids systems were prepared by laboratory-scale spray dryer (defined as S-lactose/MPI solids systems) and pilot-scale spray dryer (defined as L-lactose/MPI solids systems). Particles of L-lactose/MPI solids systems had more rounded shape, and smoother surface than those of S-lactose/MPI solids systems. Water sorption study showed S-lactose/MPI solids systems sorbed 5–30% larger amount of water than L-lactose/MPI solids systems after equilibrated at different water activities (0.11 aw–0.44 aw). Besides, comparing the samples with same composition, dairy solids with small size particles showed higher steady water content at the end of lactose crystallisation. Moreover, S-lactose/MPI solids systems showed lower glass transition temperature (Tg) values than L-lactose/MPI solids systems after equilibration at 0.11 aw, 0.23 aw and 0.33 aw, which might be due to the higher water content of S-lactose/MPI solids systems. The study of mechanical properties indicated the stiffness of S-lactose/MPI solids systems was higher than that of L-lactose/MPI solids systems at 0.23 aw and 0.33 aw when temperature was below Tg values. Water plasticization showed stronger effect on relaxation process of dairy solids with smaller size particles.

Effect of spray dryer settings on the morphology of illite clay granules

<p class="R-AbstractKeywords"><span lang="X-NONE">Spray drying is an effective and common method for powder drying, e.g. clay. The morphology and properties of spray dried granules depend on properties of slurry and operational conditions of spray dryer. The aim of this study was to investigate the effect of spray dryer settings on the morphology of illite clay granules. </span></p><p class="R-AbstractKeywords"><span lang="X-NONE">Laboratory scale spray dryer was used. Operational conditions: inlet temperature 190-220˚C, outlet temperature 70-96˚C, spray dispersion is obtained using two-fluid nozzle where the slurry feed was varied from 4.5 to 15 ml/min and gas pressure 15-40 mm. Slurry was prepared from clay fraction under 2 µm without additives. Latvian illite clay from Iecava, Pavāri and Laža deposits was studied. Slurries with concentration 1, 8 and 15 mass% was used.The size and morphology was investigated by scanning electron microscopy, surface area and porosity by liquid nitrogen sorption.</span></p><p class="R-AbstractKeywords"><span lang="X-NONE">All obtained granules irrespective of </span><span lang="X-NONE">spray dryer settings</span><span lang="X-NONE"> were well-rounded and dense without large pores or holes, however the surface was rough. The mean diameter of granules was in range of 2.6-5.4 µm, depending on slurry feed rate. The surface area of produced granules mostly depended on clay composition and was in a range of 70-92 m2/g. Inlet temperature in a range of 190-220 °C was found to be appropriate to produce well dried clay granules (moisture content <10 wt%). </span></p>

Formulation, stability and pharmacokinetics of sugar-based salmon calcitonin-loaded nanoporous/nanoparticulate microparticles (NPMPs) for inhalation

A challenge exists to produce dry powder inhaler (DPI) formulations with appropriate formulation stability, biological activity and suitable physicochemical and aerosolisation characteristics that provide a viable alternative to parenteral formulations. The present study aimed to produce sugar-based nanoporous/nanoparticulate microparticles (NPMPs) loaded with a therapeutic peptide – salmon calcitonin (sCT). The physicochemical properties of the powders and their suitability for pulmonary delivery of sCT were determined. Production of powders composed of sCT loaded into raffinose or trehalose with or without hydroxypropyl-β-cyclodextrin was carried out using a laboratory scale spray dryer. Spray dried microparticles were spherical, porous and of small geometric size (≤2μm). Aerodynamic assessment showed that the fine particle fraction (FPF) less than 5μm ranged from 45 to 86%, depending on the formulation. The mass median aerodynamic diameter (MMAD) varied between 1.9 and 4.7μm. Compared to unprocessed sCT, sCT:raffinose composite systems presented a bioactivity of approximately 100% and sCT:trehalose composite systems between 70–90% after spray drying. Storage stability studies demonstrated composite systems with raffinose to be more stable than those containing trehalose. These sugar-based salmon calcitonin-loaded NPMPs retain reasonable sCT bioactivity and have micromeritic and physicochemical properties which indicate their suitability for pulmonary delivery. Formulations presented a similar pharmacokinetic profile to sCT solution. Hence the advantage of a dry powder formulation is its non-invasive delivery route and ease of administration of the sCT.

Microencapsulation of Lactobacillus casei by spray drying

This study evaluates the use of spray drying to produce microparticles of Lactobacillus casei. Microorganism was cultivated in shaken flasks and the microencapsulation process was performed using a laboratory-scale spray dryer. A rotational central composite design was employed to optimise the drying conditions. High cell viability (1.1 × 1010 CFU/g) was achieved using an inlet air temperature of 70 °C and 25% (w/v) of maltodextrin. Microparticles presented values of solubility, wettability, water activity, hygroscopicity and humidity corresponding to 97.03 ± 0.04%, 100% (in 1.16 min), 0.14 ± 0.0, 35.20 g H2O/100 g and 4.80 ± 0.43%, respectively. The microparticles were spherical with a smooth surface and thermally stable. Encapsulation improved the survival of L. casei during storage. After 60 days, the samples stored at −8 °C showed viable cell concentrations of 1.0 × 109 CFU/g.

Co-spray dried carbohydrate microparticles: crystallisation delay/inhibition and improved aerosolization characteristics through the incorporation of hydroxypropyl-β-cyclodextrin with amorphous raffinose or trehalose.

To formulate and investigate the physicochemical properties, physical stability and aerosolization characteristics of nanoporous/nanoparticulate microparticles (NPMPs) prepared by co-spray drying the sugars raffinose pentahydrate (R) or trehalose dihydrate (T) with the cyclic oligosaccharide hydroxypropyl-β-cyclodextrin (HPβCD). Production of powders was carried out using a laboratory scale spray dryer. The resulting powders were characterised by X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), laser diffraction particle sizing, specific surface area analysis (SSA), Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), dynamic vapour sorption (DVS) and aerodynamic assessment using a Next Generation Impactor (NGI). Powders were amorphous and composed of spherical, porous microparticles with reduced particle size and high specific surface area (~100m(2)/g). DSC scans showed a single glass transition temperature. FTIR was indicative of the existence of molecular interactions between the carbohydrates. DVS analysis showed an increase in the critical relative humidity (RH) of raffinose and trehalose and eventual crystallization inhibition with increasing concentration of HPβCD. The in vitro deposition showed powders formulated with HPβCD had higher recovered emitted dose and fine particle fraction (<5μm) than raffinose and trehalose spray dried alone. The co-spray drying of raffinose or trehalose with HPβCD results in powders with improved physicochemical characteristics, physical stability and aerodynamic behaviour compared to spray-dried raffinose/trehalose particles, constituting improved potential drug-carrier systems for pulmonary delivery.

Effect of carrier agents on physical and microstructural properties of spray dried tamarind pulp powder

The aim of the present research was to investigate the effect of carrier type and its addition rate on physical and microstructural properties of spray dried tamarind pulp powder. A tall type laboratory scale spray dryer was employed for spray drying process and maltodextrin-DE 20, gum arabic and whey protein concentrate were used as carrier agents. All the carrier agents showed improvement in product recovery on increasing their concentration in feed material, with whey protein concentrate giving a higher product recovery of 76.23%. Color properties and moisture content of the powder samples were significantly affected by the carrier type and its addition rate, with moisture content ranging from 3.65 to 7.11%. Bulk density and hygroscopicity of the powders decreased with increase in concentration of the carrier agent in the feed material and powders with WPC showed lower values of hygroscopicity. Dispersibility of the powders ranged from 68.08 to 79.63, which is within the desired range. Microstructural analysis of TPPs revealed powder particles of various sizes and shapes (spherical, irregular and shrunk).

Solid-phase crystallization of spray-dried glucose powders: A perspective and comparison with lactose and sucrose

The solid-phase crystallization growth kinetics of spray-dried sugar powders, including glucose, lactose and sucrose, have been studied from water-induced crystallization experiments at a relative humidity of 75% and temperatures from 15 to 40°C on amorphous powders of these sugars produced in a laboratory-scale spray dryer (Buchi B290). All results have shown that the enthalpies and Gibbs Free Energies of activation of the sugars studied here increase during the crystallization process, suggesting that the binding energy needed for the formation of an activated complex increases as the moisture content decreases. The enthalpies of activation for glucose, lactose and sucrose crystallization have been compared by the Activated Rate equation and found to be 58±8kJmol−1, 39±2kJmol−1 and 68±4kJmol−1, for glucose, lactose and sucrose, respectively, Similarly, the entropies of activation have been calculated as −92±27Jmol−1K−1, −156±6Jmol−1K−1 and −60±5Jmol−1K−1 for glucose, lactose and sucrose, respectively. These different numerical values may be expected from the different structures of the sugars.

Drug–Polymer Miscibility across a Spray Dryer: A Case Study of Naproxen and Miconazole Solid Dispersions

The structural and physical stability of solid dispersions have not been adequately explored during spray drying manufacturing processes. In this study a wide range of compositions of naproxen/PVP-VA 64 (poly(1-vinylpyrrolidone-co-vinyl acetate)) and miconazole/PVP-VA 64 solid dispersions prepared by different laboratory spray dryers were collected from various selected locations and used to investigate the drug-polymer mixing across spray dryers. Spray-dried dispersions with 30% (w/w) naproxen collected from the transport tube of the Pro-C-epT Microspray dryer showed the narrowest glass transition width, which apparently indicates the highest degree of drug-polymer mixing compared to the other locations. The intensity of the naproxen-PVP-VA 64 interaction peak at 1654 cm(-1) of IR spectra differs for solid dispersions (SDs) from the collector and transport tube of Pro-C-epT Microspray dryer with a higher intensity for the latter. Samples with 50% (w/w) naproxen loading collected from the cyclone and the cyclone steel part of the Buchi mini spray dryer showed a melting endotherm (Tm at 112.2 ± 0.8 °C and ΔHf between 0.7 and 1.8 J/g), whereas samples from the cyclone tube to the drying chamber were devoid of crystalline material. The variations in drug-polymer mixing extend to miconazole/PVP-VA solid dispersions where 20% drug loading showed location-dependent drug-polymer mixing. This study clearly showed that the variation in drug-polymer miscibility and solid form of the drug in solid dispersions can occur across spray dryer in small-scale manufacturing processes. The optimization of formulation parameters and spray drying process parameters is imperative to diminish these variations to enhance homogeneity of solid dispersions in laboratory scale spray dryers. The same problem can occur in geometrically large spray drying manufacturing equipment, and the robustness of the processes should be carefully assessed.

Development of an axisymmetric population balance model for spray drying and validation against experimental data and CFD simulations

An incremental model for spray drying, including a full droplet size distribution, has been implemented in a flowsheeting package incorporating tracking of distributed particle properties. Results were compared with expected trends based on standard theory and with results from a laboratory-scale spray dryer with a two-fluid nozzle for atomization. Predicted trends were as expected, with larger droplets giving substantially longer drying times and higher final moisture content. Predicted final moisture content was lower than measured values, as the very short residence times for fine particles were inadequately represented by first-order falling-rate drying kinetics. Dryer gas flow patterns were simulated by computational fluid dynamics. Calculated droplet residence times were much lower than for a plug-flow or fully mixed gas flow, because a high-velocity gas flow zone from the two-fluid atomizer persists down a substantial part of the dryer.

Solid-phase crystal growth kinetics of spray-dried glucose powders

To understand the solid-phase crystallization growth kinetics of glucose powders, a laboratory-scale spray dryer (Buchi B290) was used with aqueous solutions of glucose to create amorphous powders. The amorphous powders were placed in a sorption box at a relative humidity of 75% and six different temperatures (15°C, 20°C, 25°C, 30°C, 35°C and 40°C) for water-induced crystallization. The experimental results showed that the enthalpy and Gibbs free energy of activation of glucose increased during the crystallization process, which suggested that the binding energy needed for the formation of an activated complex increases as the moisture content decreases. The energy of activation for glucose crystallization has been found by the activated rate equation to be 58±8kJmol−1, and the entropy of activation was found to be −92±27Jmol−1K−1. A linear plot of compensation between the enthalpy and entropy of activation suggests that solid-phase crystallization for glucose is an entropy-controlled process.

The Effect of Different Plasticizers on Lactose Crystallization During Spray Drying

Lactose crystallization may occur during spray drying, depending on the operating conditions for drying, and this work reviews previous and new evidence for the effects of different additives or plasticizers on retarding or accelerating the rate of crystallization. The effects of different operating conditions during spray drying are also considered in the experimental work reviewed and performed here, which was mainly carried out with Buchi B-290 laboratory-scale spray dryers (Buchi, Flawil, Switzerland), although some work on pilot-scale equipment is also discussed. The additives used and reviewed in this article include milk proteins, such as casein and whey protein isolate, polyethylene glycol, and ascorbic acid. The key physical properties, such as glass transition temperature and drying characteristics of the material, are discussed, allowing degrees of amorphicity in spray-dried lactose to be controlled over a wide range, from close to 0% to nearly 100%.

Spray Drying of Monoclonal Antibodies: Investigating Powder-Based Biologic Drug Substance Bulk Storage

Biologic drug substances (DSs) are stored and transported as frozen bulk in various containers, each having disadvantages. We evaluated a powder-based bulk storage approach based on spray drying and demonstrate for the first time that monoclonal antibodies (mAbs) can be spray dried with >90% powder collection yield using a laboratory-scale spray dryer, which outperformed three benchtop units in yield and water content reduction. Cyclone design was critical to collection yield, which remained sensitive to sample formulations. High yield was achieved for three mAbs formulated at a 2:1 mAb: trehalose weight ratio. Increasing the amount of trehalose beyond this ratio decreased yield by increasing the amount of powder retained in the drying chamber, apparently due to increased particle tackiness. Despite a high inlet temperature, the physical stability of spray-dried mAbs was comparable to or greater than that of freeze-dried counterparts. Water content of the spray-dried powder was affected more by gas residence time in the dryer than by outlet and inlet temperatures. The laboratory-scale unit, which allowed longer gas residence time, produced drier powders even at high liquid feed rate. Characterization of spray-dried mAb reconstitution time and reconstituted solution turbidity demonstrated that the process was suitable for powder-based biologic DS bulk storage applications.

Influence of Emulsion Properties on the Microencapsulation of Orange Essential Oil by Spray Drying

This work aimed to study the effect of emulsion properties on the microencapsulation of orange essential oil by spray drying. The study was performed using a 2 central composite design, where the independent variables were the total solid content (0-30%), the ratio of oil/total solids (0-30%) and the homogenization pressure used for emulsification (0-1000 bar). Whey protein concentrate and 20 DE maltodextrin, mixed in a 1:3 ratio, were used as wall materials. The emulsions were first prepared by blending the oil and the wall solution, using a rotor-stator blender; they were further emulsified using a high pressure homogenizer. All emulsions were characterized for viscosity and droplets mean diameter. Microencapsulation was performed in a laboratory scale spray dryer and particles were characterized for total and surface oil content. From these results, encapsulation efficiency and oil retention were calculated and analyzed as responses, being used for process optimization. In general, the best process responses were obtained at moderate homogenization pressures (400-650 bar), in which emulsions had the smallest droplet diameters. Higher solid content and lower oil concentration resulted in higher encapsulation efficiency and greater flavor retention, which was attributed to the higher viscosity and smaller droplet size presented by the emulsions produced under these conditions.

Impact of the spray drying conditions and residence time distribution on lysine loss in spray dried infant formula

The essential amino acid lysine plays an important role for the nutritional quality of infant formula. Unfortunately, it is easily damaged during spray drying which is usually used to produce infant formula powders. In this study, we showed that the extent of lysine loss can be controlled by adjusting the air inlet temperature and the air-to-liquid ratio. Depending on the spray drying conditions, 10.4 ± 2.9% lysine loss down to no lysine loss was determined after spray drying in laboratory scale and in pilot scale. A main impact on lysine loss could be attributed to the particle residence time which was shown to be longer for the short-form, pilot-scale spray dryer than for the tall-form, laboratory-scale spray dryer. Median particle residence time was 6 s in the laboratory scale dryer and 17 s in the pilot scale dryer. The air-to-liquid ratio of the spray dryer proved to be a good parameter to compare different types of spray dryers. The extent of lysine loss during storage of the spray dried powders was independent of the extent of lysine loss during spray drying. Lysine loss during storage can be reduced by low storage temperatures and low water contents of the powder. Coupling kinetics of lysine loss that take into account the physical state of lactose, i.e., glassy, rubbery, or crystalline, with the processing conditions and particle residence time during spray drying was shown to be a promising tool to improve the nutritional quality of spray dried infant formula.

Kinetic Modeling of Reactive Absorption of Carbon Dioxide in a Spray Dryer

AbstractA semi‐empirical kinetic correlation was obtained through a shrinking core model assumption for reactive absorption of CO2 with NaOH solution by applying response surface method analogy in a laboratory‐scale spray‐dryer absorber. The effect of approach temperature, absorbent concentration, nozzle diameter, and L/G ratio on the kinetic coefficient was studied and the optimum operating conditions to reach the maximum absorption were determined.

The Effect of Dryer Inlet and Outlet Air Temperatures and Protectant Solids on the Survival of Lactococcus lactis during Spray Drying

The influence of spray-drying conditions, inlet air temperature (130°C to 200°C), outlet air temperature (38°C to 65°C), drying medium (air and nitrogen) and milk-derived protectants (10%, 15%, and 25% lactose; 5% and 10% sodium caseinate; 10%, 25%, and 35% lactose:sodium caseinate (Lac:NaCas, 3:1)) on the survival of Lactococcus lactis ssp. cremoris was studied using a laboratory-scale spray dryer. An inlet air temperature of 130°C and 65°C as the outlet air temperature maintained high survival of the bacteria without sacrificing low moisture content. Inlet air temperature, previously considered to have no significant effect, was shown to play an important role in the survival of bacteria during spray drying. A mixture of Lac:NaCas (3:1) showed a better protective effect on the survival of bacteria than lactose and sodium caseinate individually, and this effect increased with increasing amount of protectant. The results were generalized by substituting whey protein isolate for sodium caseinate. Finally, the positive effect of elimination of oxygen was demonstrated both by replacing air with nitrogen and adding ascorbic acid as an oxygen scavenger to improve survival of the bacteria. Adding an oxygen scavenger would be a better candidate for industrial application considering the potential high cost of manufacturing if nitrogen was used as the atomization and/or drying medium.

Survival, fermentation activity and storage stability of spray dried Lactococcus lactis produced via different atomization regimes

Dried powders containing Lactococcus lactis ssp. cremoris were produced using laboratory and pilot scale spray dryers with lactose:whey protein isolate (3:1) as a protective medium. The effects of storage temperature (25, 4 and −18°C) and time (30, 60 and 90days) were studied. The survival and fermentation activity of the dried bacterial cells were significantly lower when the powders were stored at 25°C compared to those stored at 4 and −18°C; powders stored at 4 and −18°C were statistically similar. The survival and fermentation activity of bacterial cells obtained from a laboratory scale two-fluid nozzle spray dryer were found to be higher than those of cells obtained from a pilot scale two-fluid spray dryer. A rotary wheel atomizer gave significantly higher survival and activity in the same dryer. These observations are consistent with cell damage due to high characteristic shear rates in the atomization process in nozzle type atomizers. The presence of ascorbic acid (oxygen scavenger) in the powder composition was found to improve both the survival and the maintenance of fermentation activity of the dried bacterial cells significantly during storage. The survival and fermentation activity of dried bacterial cells in stored powders indicated that these parameters are system-specific and can be strongly affected by the storage temperature and presence or absence of antioxidant, and also by upstream processing conditions such as the mode of atomization and presence or absence of antioxidants in the dryer feed.