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Steven L. Nail - One of the best experts on this subject based on the ideXlab platform.
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The Influence of Mannitol Hemihydrate on the Secondary Drying Dynamics of a Protein Formulation: A Case Study
Journal of pharmaceutical sciences, 2017Co-Authors: Jayasree M. Srinivasan, Lindsay A. Wegiel, Lisa M. Hardwick, Steven L. NailAbstract:The objective of this research was to study the atypical Secondary Drying dynamics observed during the freeze-Drying of a formulation consisting of mannitol, disaccharide, and sodium chloride, where "bursts" of water vapor release were observed during Secondary Drying as detected by comparative pressure measurement. "Thief" samples were removed at the end of primary Drying and during Secondary Drying as the shelf temperature was increased in a stepwise fashion. These samples were examined by X-ray powder diffraction and thermal analysis. From the X-ray powder diffraction data, we determined that mannitol crystallized predominantly as its hemihydrate. The physical state of mannitol changed from the hemihydrate form to anhydrous forms during Secondary Drying. Investigation of the effect of excipients on mannitol crystallization demonstrated that sodium chloride (at 225 mM, 1.3% w/v) had the greatest influence on hemihydrate crystallization, followed by trehalose and sucrose. However, only negligible hemihydrate formation was observed when mannitol was freeze-dried either by itself or in the presence of 150 mM sodium chloride and no hemihydrate in the presence of 75 mM sodium chloride. In general, a combination of a disaccharide and sodium chloride promoted the hemihydrate formation to a greater extent than the individual components. Comparative pressure measurement was demonstrated to be an effective tool to monitor mannitol hemihydrate dehydration during Secondary Drying.
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A proposed rationale and test methodology for establishment of acceptance criteria for vacuum integrity testing of pharmaceutical freeze dryers.
European journal of pharmaceutics and biopharmaceutics : official journal of Arbeitsgemeinschaft fur Pharmazeutische Verfahrenstechnik e.V, 2013Co-Authors: Lisa M. Hardwick, Steven L. Nail, James Jarman, Kai Hasler, Thomas HenseAbstract:A scientific rationale is proposed for the establishment of acceptance criteria for leak rates in pharmaceutical freeze dryers. A method was developed to determine the quantity of air that could leak into any lyophilizer from the outside while still maintaining Class 100/Grade A microbial conditions. A lyophilizing product is assumed most vulnerable to microbial contamination during Secondary Drying, when mass transfer of water vapor from product to condenser is minimal. Using the void volume of the dryer, calculated from change in internal pressure when a known volume of air is introduced, and the potential maximum bioburden of the leaked air (based on measured values), calculations can determine the allowable leaked volume of air, the flow rate required to admit that volume in a given time frame, and the pressure rise that would result from the leak over a given testing period. For the dryers in this study, using worst-case air quality conditions, it was determined that a leak resulting in a pressure rise of 0.027 mbar over a 30 min period would allow the dryers to remain in Secondary Drying conditions for 62 h before the established action level of one colony forming unit for each cubic meter of air space would be reached.
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freeze Drying of tert butyl alcohol water cosolvent systems effects of formulation and process variables on residual solvents
Journal of Pharmaceutical Sciences, 1998Co-Authors: Sakchai Wittayaareekul, Steven L. NailAbstract:The objective of this study was to identify significant formulation and processing variables affecting levels of tert-butyl alcohol (TBA) and isopropyl alcohol (IPA) in freeze-dried solids prepared from TBA/water cosolvent systems. The variables examined were the physical state of the solute (crystalline vs amorphous), initial TBA concentration, freezing rate, cake thickness, and the temperature and duration of Secondary Drying. Sucrose and glycine were used as models for noncrystallizing and crystallizing solutes, respectively. The TBA concentration above which eutectic crystallization takes place was determined by differential scanning calorimetry. Model formulations were subjected to extremes of freezing rate by either dipping in liquid nitrogen or by slowly freezing on the shelf of a freeze-dryer. Dynamics of solvent loss during Secondary Drying was determined by withdrawing samples as a function of time at different shelf temperatures using a thief system. On the basis of these studies, the most important determinant of residual TBA level is the physical state of the solute. Freeze-dried glycine contained very low levels of residual TBA (0.01-0.03%) regardless of freezing rate or initial TBA concentration. For freeze-dried sucrose, residual TBA levels were approximately 2 orders of magnitude higher and were significantly affected by initial TBA concentration and freezing rate. For the sucrose/TBA/water system, relatively low residual TBA levels were obtained when the initial TBA level was above the threshold concentration for eutectic crystallization of TBA, whereas samples freeze-dried from solutions containing TBA concentrations below this threshold contained significantly higher levels of TBA. Residual IPA levels increased continuously with initial concentration of TBA in the sucrose/TBA/water system. Formulations of sucrose/TBA/water which were frozen rapidly contained residual TBA levels which were approximately twice those measured in the same formulation after slow freezing and Drying under the same conditions. For the sucrose/TBA/water system, the temperature and time of Secondary Drying had only minimal influence on residual TBA in the freeze-dried solid. At low initial TBA concentrations (2%), residual TBA increases with increased cake thickness, perhaps because of the influence of depth of fill on effective freezing rate.
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Freeze-Drying of tert-Butyl Alcohol/Water Cosolvent Systems: Effects of Formulation and Process Variables on Residual Solvents
Journal of pharmaceutical sciences, 1998Co-Authors: Sakchai Wittaya-areekul, Steven L. NailAbstract:The objective of this study was to identify significant formulation and processing variables affecting levels of tert-butyl alcohol (TBA) and isopropyl alcohol (IPA) in freeze-dried solids prepared from TBA/water cosolvent systems. The variables examined were the physical state of the solute (crystalline vs amorphous), initial TBA concentration, freezing rate, cake thickness, and the temperature and duration of Secondary Drying. Sucrose and glycine were used as models for noncrystallizing and crystallizing solutes, respectively. The TBA concentration above which eutectic crystallization takes place was determined by differential scanning calorimetry. Model formulations were subjected to extremes of freezing rate by either dipping in liquid nitrogen or by slowly freezing on the shelf of a freeze-dryer. Dynamics of solvent loss during Secondary Drying was determined by withdrawing samples as a function of time at different shelf temperatures using a thief system. On the basis of these studies, the most important determinant of residual TBA level is the physical state of the solute. Freeze-dried glycine contained very low levels of residual TBA (0.01-0.03%) regardless of freezing rate or initial TBA concentration. For freeze-dried sucrose, residual TBA levels were approximately 2 orders of magnitude higher and were significantly affected by initial TBA concentration and freezing rate. For the sucrose/TBA/water system, relatively low residual TBA levels were obtained when the initial TBA level was above the threshold concentration for eutectic crystallization of TBA, whereas samples freeze-dried from solutions containing TBA concentrations below this threshold contained significantly higher levels of TBA. Residual IPA levels increased continuously with initial concentration of TBA in the sucrose/TBA/water system. Formulations of sucrose/TBA/water which were frozen rapidly contained residual TBA levels which were approximately twice those measured in the same formulation after slow freezing and Drying under the same conditions. For the sucrose/TBA/water system, the temperature and time of Secondary Drying had only minimal influence on residual TBA in the freeze-dried solid. At low initial TBA concentrations (2%), residual TBA increases with increased cake thickness, perhaps because of the influence of depth of fill on effective freezing rate.
Hao Jiang - One of the best experts on this subject based on the ideXlab platform.
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changes of microwave structure dielectric properties during microwave freeze Drying process banana chips
International Journal of Food Science and Technology, 2014Co-Authors: Hao Jiang, Arun S. Mujumdar, Min Zhang, Rui X. LimAbstract:Summary This experimental study investigated the trend of structure and dielectric properties during microwave freeze-Drying process banana chips. The mass of banana samples was 160 g, the microwave power set as 2 W g−1 and the highest Drying temperature set as 55 °C. The whole Drying process can be finished within 6 h. A network analyser and light microscope were used to determine the dielectric properties and structure. The dielectric properties, e′ (from 20.80 to 1.20) and e′′ (from 7.74 to 0.15), and the size of cell get smaller as the Drying process continues, especially during the 3–4 h Drying, which is the end of primary Drying stage and the beginning of Secondary Drying stage. The trend of dielectric properties and microstructure of samples during Drying can be an exact indication of Drying stage of MFD.
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Changes of microwave structure/dielectric properties during microwave freeze‐Drying process banana chips
International Journal of Food Science and Technology, 2014Co-Authors: Hao Jiang, Arun S. Mujumdar, Min Zhang, Rui X. LimAbstract:Summary This experimental study investigated the trend of structure and dielectric properties during microwave freeze-Drying process banana chips. The mass of banana samples was 160 g, the microwave power set as 2 W g−1 and the highest Drying temperature set as 55 °C. The whole Drying process can be finished within 6 h. A network analyser and light microscope were used to determine the dielectric properties and structure. The dielectric properties, e′ (from 20.80 to 1.20) and e′′ (from 7.74 to 0.15), and the size of cell get smaller as the Drying process continues, especially during the 3–4 h Drying, which is the end of primary Drying stage and the beginning of Secondary Drying stage. The trend of dielectric properties and microstructure of samples during Drying can be an exact indication of Drying stage of MFD.
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The energy consumption and color analysis of freeze/microwave freeze banana chips
Food and Bioproducts Processing, 2013Co-Authors: Hao Jiang, Arun S. Mujumdar, Yin Liu, Min Zhang, Huihua LiuAbstract:Abstract This study investigated the energy consumption of preparing banana chips by freeze Drying (FD) and microwave freeze Drying (MFD) methods. The results in this study showed that the energy consumption for 400 g fresh banana (about 95 g dried samples) by FD process and MFD process are about 35.73 × 10 6 J (9.92 kW h) and 21.76 × 10 6 J (6.57 kW h), respectively. Compared to the traditional FD process, MFD can save up to 35.7% energy and 40% Drying time. Increasing the heating power in the Secondary Drying stage of MFD process had been confirmed to result in decrease in both the energy consumption and Drying time. After increasing the microwave power in the Secondary Drying stage from 1.0 W/g to 1.5 W/g in MFD process, total energy consumption is about 18.12 × 10 6 J (5.56 kW h) and Drying time can be reduced from 360 min to 270 min. The sensory evaluation of produced banana chips at different Drying conditions (1.0 W/g, 1.5 W/g and 2.0 W/g) revealed that the sensory properties are acceptable by the customers except the 2 W/g microwave power dried product. Thus, the method that increased the heating powder in the Secondary Drying stage of the MFD process could potentially be an effective method to reduce the energy consumption without seriously sacrificing the color of the end product.
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the energy consumption and color analysis of freeze microwave freeze banana chips
Food and Bioproducts Processing, 2013Co-Authors: Hao Jiang, Arun S. Mujumdar, Yin Liu, Min Zhang, Huihua LiuAbstract:Abstract This study investigated the energy consumption of preparing banana chips by freeze Drying (FD) and microwave freeze Drying (MFD) methods. The results in this study showed that the energy consumption for 400 g fresh banana (about 95 g dried samples) by FD process and MFD process are about 35.73 × 10 6 J (9.92 kW h) and 21.76 × 10 6 J (6.57 kW h), respectively. Compared to the traditional FD process, MFD can save up to 35.7% energy and 40% Drying time. Increasing the heating power in the Secondary Drying stage of MFD process had been confirmed to result in decrease in both the energy consumption and Drying time. After increasing the microwave power in the Secondary Drying stage from 1.0 W/g to 1.5 W/g in MFD process, total energy consumption is about 18.12 × 10 6 J (5.56 kW h) and Drying time can be reduced from 360 min to 270 min. The sensory evaluation of produced banana chips at different Drying conditions (1.0 W/g, 1.5 W/g and 2.0 W/g) revealed that the sensory properties are acceptable by the customers except the 2 W/g microwave power dried product. Thus, the method that increased the heating powder in the Secondary Drying stage of the MFD process could potentially be an effective method to reduce the energy consumption without seriously sacrificing the color of the end product.
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Physico-chemical changes during different stages of MFD/FD banana chips
Journal of Food Engineering, 2010Co-Authors: Hao Jiang, Min Zhang, Arun S. MujumdarAbstract:Abstract Microwave freeze Drying (MFD) normally contains three stages, i.e., pre-freeze stage, primary Drying stage and Secondary Drying stage, just as in conventional freeze Drying. This research examines the variations of structure, starch content, reducing sugar content, color change as well as expansion ratio during these stages of microwave freeze Drying banana chips. Results show that biggest changes are found at the primary Drying stage in the banana slices’ starch content, reduced sugar content, their structure and their changed colors while the biggest change of expansion ratio occurs at the Secondary Drying stage. Similar results can also be obtained for FD samples. Thus it is concluded that the primary stage can do most damage to the banana chips.
Michael J. Pikal - One of the best experts on this subject based on the ideXlab platform.
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Modeling the Secondary Drying Stage of Freeze Drying: Development and Validation of an Excel-Based Model
Journal of pharmaceutical sciences, 2016Co-Authors: Ekneet Kaur Sahni, Michael J. PikalAbstract:Although several mathematical models of primary Drying have been developed over the years, with significant impact on the efficiency of process design, models of Secondary Drying have been confined to highly complex models. The simple-to-use Excel-based model developed here is, in essence, a series of steady state calculations of heat and mass transfer in the 2 halves of the dry layer where Drying time is divided into a large number of time steps, where in each time step steady state conditions prevail. Water desorption isotherm and mass transfer coefficient data are required. We use the Excel "Solver" to estimate the parameters that define the mass transfer coefficient by minimizing the deviations in water content between calculation and a calibration Drying experiment. This tool allows the user to input the parameters specific to the product, process, container, and equipment. Temporal variations in average moisture contents and product temperatures are outputs and are compared with experiment. We observe good agreement between experiments and calculations, generally well within experimental error, for sucrose at various concentrations, temperatures, and ice nucleation temperatures. We conclude that this model can serve as an important process development tool for process design and manufacturing problem-solving.
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Optimization of the Secondary Drying Step in Freeze Drying Using TDLAS Technology
AAPS PharmSciTech, 2011Co-Authors: Stefan C. Schneid, Henning Gieseler, William J. Kessler, Suman Luthra, Michael J. PikalAbstract:The Secondary Drying phase in freeze Drying is mostly developed on a trial-and-error basis due to the lack of appropriate noninvasive process analyzers. This study describes for the first time the application of Tunable Diode Laser Absorption Spectroscopy, a spectroscopic and noninvasive sensor for monitoring Secondary Drying in laboratory-scale freeze Drying with the overall purpose of targeting intermediate moisture contents in the product. Bovine serum albumin/sucrose mixtures were used as a model system to imitate high concentrated antibody formulations. First, the rate of water desorption during Secondary Drying at constant product temperatures (−22°C, −10°C, and 0°C) was investigated for three different shelf temperatures. Residual moisture contents of sampled vials were determined by Karl Fischer titration. An equilibration step was implemented to ensure homogeneous distribution of moisture (within 1%) in all vials. The residual moisture revealed a linear relationship to the water desorption rate for different temperatures, allowing the evaluation of an anchor point from noninvasive flow rate measurements without removal of samples from the freeze dryer. The accuracy of mass flow integration from this anchor point was found to be about 0.5%. In a second step, the concept was successfully tested in a confirmation experiment. Here, good agreement was found for the initial moisture content (anchor point) and the subsequent monitoring and targeting of intermediate moisture contents. The present approach for monitoring Secondary Drying indicated great potential to find wider application in sterile operations on production scale in pharmaceutical freeze Drying.
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determination of end point of primary Drying in freeze Drying process control
Aaps Pharmscitech, 2010Co-Authors: Sajal M. Patel, Takayuki Doen, Michael J. PikalAbstract:Freeze-Drying is a relatively expensive process requiring long processing time, and hence one of the key objectives during freeze-Drying process development is to minimize the primary Drying time, which is the longest of the three steps in freeze-Drying. However, increasing the shelf temperature into Secondary Drying before all of the ice is removed from the product will likely cause collapse or eutectic melt. Thus, from product quality as well as process economics standpoint, it is very critical to detect the end of primary Drying. Experiments were conducted with 5% mannitol and 5% sucrose as model systems. The apparent end point of primary Drying was determined by comparative pressure measurement (i.e., Pirani vs. MKS Baratron), dew point, Lyotrack (gas plasma spectroscopy), water concentration from tunable diode laser absorption spectroscopy, condenser pressure, pressure rise test (manometric temperature measurement or variations of this method), and product thermocouples. Vials were pulled out from the Drying chamber using a sample thief during late primary and early Secondary Drying to determine percent residual moisture either gravimetrically or by Karl Fischer, and the cake structure was determined visually for melt-back, collapse, and retention of cake structure at the apparent end point of primary Drying (i.e., onset, midpoint, and offset). By far, the Pirani is the best choice of the methods tested for evaluation of the end point of primary Drying. Also, it is a batch technique, which is cheap, steam sterilizable, and easy to install without requiring any modification to the existing dryer.
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Impact of critical process and formulation parameters affecting in‐process stability of lactate dehydrogenase during the Secondary Drying stage of lyophilization: A mini freeze dryer study
Journal of pharmaceutical sciences, 2007Co-Authors: Sumit Luthra, Jean-philippe Obert, Devendra S. Kalonia, Michael J. PikalAbstract:The stresses during the Secondary-Drying stage of lyophilization were investigated using a controlled humidity mini-freeze-dryer [Luthra S, Obert J-P, Kalonia DS, Pikal MJ. 2007. Investigation of Drying stresses on proteins during lyophilization: Differentiation between primary and Secondary-Drying stresses on lactate dehydrogenase using a humidity controlled mini freeze-dryer. J Pharm Sci 96: 61-70.]. Lactate dehydrogenase (LDH), was formulated in: (1) Tween 80, (2) citrate buffer, and (3) both Tween 80 and citrate buffer. Protein activity recovery was measured as a function of relative humidity (RH), product temperature, and Drying duration. Studies were also conducted with different concentrations of sucrose, sorbitol, and poly (vinyl pyrrolidone) (PVP). LDH stability was affected to a small extent by RH and significantly by Drying temperature and duration. Complete stabilization of LDH was observed when lyophilized with sucrose and PVP but only a partial stabilization was observed with sorbitol. The mini-freeze-dryer enabled studying the process parameters independently, unlike a conventional study where these effects are generally convoluted. The results suggest that the stability of the protein is a function of the dynamics of the system during lyophilization. The origin of the stabilization effect of sucrose, which could, in principle, be attributed both to direct interaction with the protein or vitrification of the protein was elucidated using lyoprotectants that can either hydrogen bond well with the protein (sorbitol) or form a good glass (PVP). It appears both effects are required for complete stabilization of the protein.
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investigation of Drying stresses on proteins during lyophilization differentiation between primary and Secondary Drying stresses on lactate dehydrogenase using a humidity controlled mini freeze dryer
Journal of Pharmaceutical Sciences, 2007Co-Authors: Sumit Luthra, Jean-philippe Obert, Devendra S. Kalonia, Michael J. PikalAbstract:This article describes the design, performance testing, and application of a controlled humidity mini-freeze-dryer in studying the physical stability of lactate dehydrogenase during lyophilization. Performance evaluation of the mini-freeze-dryer was conducted with tests, namely water sublimation, radiation heat exchange, lowest achievable temperature, and leak testing. Protein stability studies were conducted by comparing protein activity at various stages of lyophilization with the initial activity. The shelf and condenser temperature were stable at <-40 degrees C, wall temperature was within 2 degrees C of the shelf temperature, and the leak rate was small. The chamber pressure was controlled by the ice on the condenser and the product temperature during sublimation was equal to the shelf temperature. Addition of Tween 80 prevented activity loss in solution and after freeze-thaw. No activity loss was observed after primary-Drying even in absence of lyoprotectants and with collapse of cake structure. Five percent (w/w) sucrose concentration was required to achieve full stabilization. In conclusion, performance testing established that the mini-freeze-dryer was suitable for mechanistic freeze-Drying studies. Secondary-Drying was the critical step for protein stability. The concentration of sucrose required to stabilize the protein completely was several orders of magnitude higher than that required to satisfy the direct interaction requirement of the protein.
Arun S. Mujumdar - One of the best experts on this subject based on the ideXlab platform.
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changes of microwave structure dielectric properties during microwave freeze Drying process banana chips
International Journal of Food Science and Technology, 2014Co-Authors: Hao Jiang, Arun S. Mujumdar, Min Zhang, Rui X. LimAbstract:Summary This experimental study investigated the trend of structure and dielectric properties during microwave freeze-Drying process banana chips. The mass of banana samples was 160 g, the microwave power set as 2 W g−1 and the highest Drying temperature set as 55 °C. The whole Drying process can be finished within 6 h. A network analyser and light microscope were used to determine the dielectric properties and structure. The dielectric properties, e′ (from 20.80 to 1.20) and e′′ (from 7.74 to 0.15), and the size of cell get smaller as the Drying process continues, especially during the 3–4 h Drying, which is the end of primary Drying stage and the beginning of Secondary Drying stage. The trend of dielectric properties and microstructure of samples during Drying can be an exact indication of Drying stage of MFD.
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Changes of microwave structure/dielectric properties during microwave freeze‐Drying process banana chips
International Journal of Food Science and Technology, 2014Co-Authors: Hao Jiang, Arun S. Mujumdar, Min Zhang, Rui X. LimAbstract:Summary This experimental study investigated the trend of structure and dielectric properties during microwave freeze-Drying process banana chips. The mass of banana samples was 160 g, the microwave power set as 2 W g−1 and the highest Drying temperature set as 55 °C. The whole Drying process can be finished within 6 h. A network analyser and light microscope were used to determine the dielectric properties and structure. The dielectric properties, e′ (from 20.80 to 1.20) and e′′ (from 7.74 to 0.15), and the size of cell get smaller as the Drying process continues, especially during the 3–4 h Drying, which is the end of primary Drying stage and the beginning of Secondary Drying stage. The trend of dielectric properties and microstructure of samples during Drying can be an exact indication of Drying stage of MFD.
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The energy consumption and color analysis of freeze/microwave freeze banana chips
Food and Bioproducts Processing, 2013Co-Authors: Hao Jiang, Arun S. Mujumdar, Yin Liu, Min Zhang, Huihua LiuAbstract:Abstract This study investigated the energy consumption of preparing banana chips by freeze Drying (FD) and microwave freeze Drying (MFD) methods. The results in this study showed that the energy consumption for 400 g fresh banana (about 95 g dried samples) by FD process and MFD process are about 35.73 × 10 6 J (9.92 kW h) and 21.76 × 10 6 J (6.57 kW h), respectively. Compared to the traditional FD process, MFD can save up to 35.7% energy and 40% Drying time. Increasing the heating power in the Secondary Drying stage of MFD process had been confirmed to result in decrease in both the energy consumption and Drying time. After increasing the microwave power in the Secondary Drying stage from 1.0 W/g to 1.5 W/g in MFD process, total energy consumption is about 18.12 × 10 6 J (5.56 kW h) and Drying time can be reduced from 360 min to 270 min. The sensory evaluation of produced banana chips at different Drying conditions (1.0 W/g, 1.5 W/g and 2.0 W/g) revealed that the sensory properties are acceptable by the customers except the 2 W/g microwave power dried product. Thus, the method that increased the heating powder in the Secondary Drying stage of the MFD process could potentially be an effective method to reduce the energy consumption without seriously sacrificing the color of the end product.
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the energy consumption and color analysis of freeze microwave freeze banana chips
Food and Bioproducts Processing, 2013Co-Authors: Hao Jiang, Arun S. Mujumdar, Yin Liu, Min Zhang, Huihua LiuAbstract:Abstract This study investigated the energy consumption of preparing banana chips by freeze Drying (FD) and microwave freeze Drying (MFD) methods. The results in this study showed that the energy consumption for 400 g fresh banana (about 95 g dried samples) by FD process and MFD process are about 35.73 × 10 6 J (9.92 kW h) and 21.76 × 10 6 J (6.57 kW h), respectively. Compared to the traditional FD process, MFD can save up to 35.7% energy and 40% Drying time. Increasing the heating power in the Secondary Drying stage of MFD process had been confirmed to result in decrease in both the energy consumption and Drying time. After increasing the microwave power in the Secondary Drying stage from 1.0 W/g to 1.5 W/g in MFD process, total energy consumption is about 18.12 × 10 6 J (5.56 kW h) and Drying time can be reduced from 360 min to 270 min. The sensory evaluation of produced banana chips at different Drying conditions (1.0 W/g, 1.5 W/g and 2.0 W/g) revealed that the sensory properties are acceptable by the customers except the 2 W/g microwave power dried product. Thus, the method that increased the heating powder in the Secondary Drying stage of the MFD process could potentially be an effective method to reduce the energy consumption without seriously sacrificing the color of the end product.
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Physico-chemical changes during different stages of MFD/FD banana chips
Journal of Food Engineering, 2010Co-Authors: Hao Jiang, Min Zhang, Arun S. MujumdarAbstract:Abstract Microwave freeze Drying (MFD) normally contains three stages, i.e., pre-freeze stage, primary Drying stage and Secondary Drying stage, just as in conventional freeze Drying. This research examines the variations of structure, starch content, reducing sugar content, color change as well as expansion ratio during these stages of microwave freeze Drying banana chips. Results show that biggest changes are found at the primary Drying stage in the banana slices’ starch content, reduced sugar content, their structure and their changed colors while the biggest change of expansion ratio occurs at the Secondary Drying stage. Similar results can also be obtained for FD samples. Thus it is concluded that the primary stage can do most damage to the banana chips.
Athanasios I Liapis - One of the best experts on this subject based on the ideXlab platform.
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The Drying rates of spray freeze Drying systems increase through the use of stratified packed bed structures
International Journal of Heat and Mass Transfer, 2015Co-Authors: R. Bruttini, Athanasios I LiapisAbstract:Abstract It is shown that when in the spray freeze Drying process stratified packed beds are employed where the smallest in size particles are located near the surface of the lower heating plate while the largest particles are occupying the upper part of the stratified packed bed whose outermost surface is in contact with the atmosphere of the Drying chamber of the freeze dryer, the duration times of the primary and Secondary Drying stages can be substantially reduced when compared with those required by a spray freeze Drying process which uses a single packed bed formed by particles all having the same particle size and the total amount of solids in the packed bed is the same as that in the stratified packed bed.
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Exergy analysis of freeze-Drying of pharmaceuticals in vials on trays.
International Journal of Heat and Mass Transfer, 2008Co-Authors: Athanasios I Liapis, R. BruttiniAbstract:The expressions for determining the exergy inputs and exergy losses due to heat and mass transfer in the primary and Secondary Drying stages as well as in the water vapor condenser and vacuum pump of the lyophilization process involving freeze Drying of pharmaceuticals in vials on trays, are constructed and presented in this work. The structures of the exergy expressions indicate the importance of the magnitude of the duration times of the primary and Secondary Drying stages as well as those of the gradient of temperature and of the pressure gradients of water vapor and inerts in the material being dried, on the magnitude of the exergy inputs and exergy losses. This information is then used to indicate policies for the control variables of the lyophilization process that can result in reductions in the exergy losses in the primary and Secondary Drying stages, as well as in the water vapor condenser and in the vacuum pump system for heat-transfer and mass-transfer controlled freeze Drying processes. The distribution of the exergy inputs and exergy losses for a lyophilization system are presented and the results show that most of the exergy input is consumed and most of the exergy losses result by the primary Drying stage, the water vapor condenser, and vacuum pump in that order. By using the exergy expressions presented in this work operational control policies can be constructed that minimize the irreversibilities occurring in the operations of a freeze Drying system of a given design, thus enhancing the efficiency of energy utilization in lyophilization.
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freeze Drying of pharmaceuticals in vials on trays effects of Drying chamber wall temperature and tray side on lyophilization performance
International Journal of Heat and Mass Transfer, 2005Co-Authors: Kian Hui Gan, R. Bruttini, O K Crosser, Athanasios I LiapisAbstract:Abstract The effects of tray side and Drying chamber wall temperature on the performance of freeze-Drying of pharmaceuticals in vials arranged in clusters of hexagonal arrays on trays are studied, and the results of this work indicate that it would be beneficial to operate the lyophilization process by (i) employing freeze-dryers whose trays have no tray sides, (ii) using heat input control that runs the freeze-Drying process close to the melting and scorch temperature constraints during the primary and Secondary Drying stages, respectively, and (iii) keeping the Drying chamber wall temperature slightly higher than the melting temperature constraint during the primary Drying stage, while during the Secondary Drying stage the Drying chamber wall temperature should not be significantly lower than the scorch temperature constraint. The modeling and system formulation approach presented here provide a quantitative method that can be used in the analysis, optimization and control of the lyophilization process, as well as in the design of freeze-dryers.
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Heating Policies during the Primary and Secondary Drying Stages of the Lyophilization Process in Vials: Effects of the Arrangement of Vials in Clusters of Square and Hexagonal Arrays on Trays
Drying Technology, 2004Co-Authors: Kian Hui Gan, R. Bruttini, O K Crosser, Athanasios I LiapisAbstract:Abstract The dynamic behavior of the primary and Secondary Drying stages of the lyophilization process were studied when (a) single vials located at different positions on the tray were individually being dried, and (b) the vials on the tray are arranged in clusters of square and hexagonal arrays and all the vials on the tray are simultaneously being dried. For both cases (a) and (b), fast Drying times and relatively more uniform distributions of temperature and concentration of bound water at the end of the Secondary Drying stage are obtained by heat input control that runs the lyophilization process close to the melting and scorch temperature constraints. The heating control policies for the systems of case (b) are found to be more conservative and significantly more complex than those for the systems of case (a), because in case (b) there are vials on the tray that are in their Secondary Drying stage while other vials on the same tray have not yet completed their primary Drying stage. Furthermore, the ...
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modeling of the primary and Secondary Drying stages of the freeze Drying of pharmaceutical products in vials numerical results obtained from the solution of a dynamic and spatially multi dimensional lyophilization model for different operational poli
Biotechnology and Bioengineering, 1998Co-Authors: Patrick P Sheehan, Athanasios I LiapisAbstract:A rigorous unsteady state and spatially multidimensional model is presented and solved to describe the dynamic behavior of the primary and Secondary Drying stages of the lyophilization of a pharmaceutical product in vials for different operational policies. The results in this work strongly motivate the aggressive control of freeze Drying and it is found that heat input control that runs the process close to the melting and scorch temperature constraints yields (i) faster Drying times, and (ii) more uniform distributions of temperature and concentration of bound water at the end of the Secondary Drying stage.