Recent developments in high efficient freeze-drying of fruits and vegetables assisted by microwave: A review.

Microwave heating has been applied in the drying of high-value solids as it affords a number of advantages, including shorter drying time and better product quality. Freeze-drying at cryogenic temperature and extremely low pressure provides the advantage of high product quality, but at very high capital and operating costs due partly to very long drying time. Freeze-drying coupled with a microwave heat source speeds up the drying rate and yields good quality products provided the operating unit is designed and operated to achieve the potential for an absence of hot spot developments. This review is a survey of recent developments in the modeling and experimental results on microwave-assisted freeze-drying (MFD) over the past decade. Owing to the high costs involved, so far all applications are limited to small-scale operations for the drying of high-value foods such as fruits and vegetables. In order to promote industrial-scale applications for a broader range of products further research and development efforts are needed to offset the current limitations of the process. The needs and opportunities for future research and developments are outlined.

Impact of Microscale and Pilot-Scale Freeze-Drying on Protein Secondary Structures: Sucrose Formulations of Lysozyme and Catalase.

Microscale (MS) freeze-drying offers rapid process cycles for early-stage formulation development. The effects of the MS approach on the secondary structures of two model proteins, lysozyme and catalase, were compared with pilot-scale (PS) vial freeze-drying. The secondary structures were assessed by attenuated total reflection Fourier transformed infrared spectroscopy. Formulations were made with increasing sucrose-protein ratios. Freeze-drying protocols involved regular cooling without thermal treatment and annealing with MS and PS equipment, and cooling rate variations with the MS. Principal component analysis of smoothed second-derivative amide I spectra revealed sucrose-protein ratio-dependent shifts toward α-helical structures. Transferability of sucrose-protein formulations from MS to PS vial freeze-drying was evidenced at regular cooling rates. Local differences in protein secondary structures between the bottom and top of sucrose-catalase samples could be detected at the sucrose-catalase ratios of 1 and 2, this being related to the initial filling height and ice crystal morphology. Annealing revealed temperature, protein, formulation, and sample location-dependent effects influencing surface morphology at the top, or causing protein secondary structure perturbation at the bottom. With the MS approach, protein secondary structure differences at different cooling rates could be detected for sucrose-lysozyme samples at the sucrose-lysozyme ratio of 1.

Cost-effective pooling of DNA from nasopharyngeal swab samples for large-scale detection of bacteria by real-time PCR.

We investigated the potential of pooling DNA from nasopharyngeal specimens to reduce the cost of real-time PCR (RT-PCR) for bacterial detection. Lyophilization is required to reconcentrate DNA. This strategy yields a high specificity (86%) and a high sensitivity (96%). We estimate that compared to individual testing, 37% fewer RT-PCR tests are needed.

Cost effectiveness of cryoprotective agents and modified De-man Rogosa Sharpe medium on growth of Lactobacillus acidophilus.

The effect of cryoprotective agents (namely, sodium chloride, sucrose, dextran, sorbitol, monosodium glutamate, glycerol, skim milk and skim milk with malt extract) and modified De-Man Rogosa Sharpe (MRS) medium, on the viability and stability of L. acidophilus ATCC 4962, was investigated. The modified MRS medium was not only economical, but it gave a relatively higher yield of L. acidophilus ATCC 4962 than the commercial MRS. Monosodium glutamate, skim milk and skim milk with malt extract provided significantly higher viable counts, with optimum concentration at 0.3%. Nevertheless, at concentration above 0.5%, there was a reduction in cell viability, which could be attributed to cell shrinkage associated with osmotic pressure changes inside the cells. It was also found that L. acidophilus ATCC 4962 was stable at 28 degrees C for eight weeks. Skim milk demonstrated a significant growth of probiotics. Skim milk was the preferred cryoprotective agent, as it is of low cost, easily available and demonstrated a significant growth of probiotics. In conclusion, modified MRS medium with skim milk is suggested for the remarkable growth and yield of L. acidophilus.

Comparison of product drying performance in molded and serum tubing vials using gentamicin sulfate as a model system.

In a previous study, heat transfer coefficients of different 10 mL tubing and molded vials were determined gravimetrically via sublimation tests with pure water. Contrary to "conventional wisdom", only small differences in K(v) values between tubing and molded vials were found in the pressure range relevant for pharmaceutical freeze-drying. In order to investigate the impact of these relatively small differences on the primary drying time of an actual product, freeze-drying experiments with 5% gentamicin sulfate solution as a model system were performed at 68, 100 and 200 mTorr. The primary drying times of the API in recently developed molded (EasyLyo™), tubing (TopLyo™) and polymer vials (TopPac™) were compared. At 68 and 100 mTorr the primary drying time of the drug in the glass vials only differed by 3% to 4%, while the polymer vial took around 9% longer. At 200 mTorr, the API in the EasyLyo™ vials dried approximately 15% faster compared to the other vial types. The present study suggest that molded vials that have been modified in design to have better heat transfer properties can achieve drying times comparable to tubing vials.

Toward low-cost affinity reagents: lyophilized yeast-scFv probes specific for pathogen antigens.

The generation of affinity reagents, usually monoclonal antibodies, remains a critical bottleneck in biomedical research and diagnostic test development. Recombinant antibody-like proteins such as scFv have yet to replace traditional monoclonal antibodies in antigen detection applications, in large part because of poor performance of scFv in solution. To address this limitation, we have developed assays that use whole yeast cells expressing scFv on their surfaces (yeast-scFv) in place of soluble purified scFv or traditional monoclonal antibodies. In this study, a nonimmune library of human scFv displayed on the surfaces of yeast cells was screened for clones that bind to recombinant cyst proteins of Entamoeba histolytica, an enteric pathogen of humans. Selected yeast-scFv clones were stabilized by lyophilization and used in detection assay formats in which the yeast-scFv served as solid support-bound monoclonal antibodies. Specific binding of antigen to the yeast-scFv was detected by staining with rabbit polyclonal antibodies. In flow cytometry-based assays, lyophilized yeast-scFv reagents retained full binding activity and specificity for their cognate antigens after 4 weeks of storage at room temperature in the absence of desiccants or stabilizers. Because flow cytometry is not available to all potential assay users, an immunofluorescence assay was also developed that detects antigen with similar sensitivity and specificity. Antigen-specific whole-cell yeast-scFv reagents can be selected from nonimmune libraries in 2-3 weeks, produced in vast quantities, and packaged in lyophilized form for extended shelf life. Lyophilized yeast-scFv show promise as low cost, renewable alternatives to monoclonal antibodies for diagnosis and research.

Long-term preservation of freeze-dried mouse spermatozoa.

Many genetically engineered mice strains have been generated worldwide and sperm preservation is a valuable method for storing these strains as genetic resources. Freeze-drying is a useful sperm preservation method because it requires neither liquid nitrogen nor dry ice for preservation and transportation. We report here successful long-term preservation at 4 °C of mouse spermatozoa freeze-dried using a simple buffer solution (10mM Tris, 1mM EDTA, pH 8.0). Offspring with fertility were obtained from oocytes fertilized with freeze-dried spermatozoa from C57BL/6 and B6D2F1 mouse strains stored at 4 °C for 3 years. This freeze-drying method is a safe and economical tool for the biobanking of valuable mouse strains.

In-line optimization and control of an industrial freeze-drying process for pharmaceuticals.

This paper deals with the in-line optimization and control of the freeze-drying process of pharmaceuticals in vials. The proposed control system, named LyoDriver, uses a mathematical model of the process to calculate the values of the temperature of the heating fluid: the goal is to minimize the time required to get the desired amount of residual water in the dried product, and to maintain product temperature below the maximum allowed value, thus preserving product quality. The values of product temperature and residual ice content, as well as other parameters, are required to perform the calculations: these variables are estimated in-line by means of the Dynamic Parameters Estimation algorithm, an advanced tool based on the pressure rise test, but also other monitoring systems can be used. Two different control algorithms are presented and investigated by means of mathematical simulation and experiments carried out in a small industrial-type apparatus (LyoBeta 25 by Telstar). Results show the effectiveness of LyoDriver in a wide range of operating conditions, even when the process becomes mass-transfer controlled, or when the operating pressure is changed.

Rapid determination of vial heat transfer parameters using tunable diode laser absorption spectroscopy (TDLAS) in response to step-changes in pressure set-point during freeze-drying.

The purpose of this study was to perform a rapid determination of vial heat transfer parameters, that is, the contact parameter K(cs) and the separation distance l(v), using the sublimation rate profiles measured by tunable diode laser absorption spectroscopy (TDLAS). In this study, each size of vial was filled with pure water followed by a freeze-drying cycle using a LyoStar II dryer (FTS Systems) with step-changes of the chamber pressure set-point at to 25, 50, 100, 200, 300, and 400 mTorr. K(cs) was independently determined by nonlinear parameter estimation using the sublimation rates measured at the pressure set-point of 25 mTorr. After obtaining K(cs), the l(v) value for each vial size was determined by nonlinear parameter estimation using the pooled sublimation rate profiles obtained at 25 to 400 mTorr. The vial heat transfer coefficient K(v), as a function of the chamber pressure, was readily calculated, using the obtained K(cs) and l(v) values. It is interesting to note the significant difference in K(v) of two similar types of 10 mL Schott tubing vials, primary due to the geometry of the vial-bottom, as demonstrated by the images of the contact areas of the vial-bottom.

An economic evaluation of freeze-dried kefir starter culture production using whey.

An economic study is presented in which industrial-scale production of freeze-dried kefir starter culture is discussed based on results on a laboratory scale. Industrial scale-up was based on a 3-step process using 3 bioreactors of 100, 3,000, and 30,000 L for 300 kg of freeze-dried culture/d of plant capacity. The major cost component of the total investment was the freeze-drying machinery, which consisted of 57% of the total investment. Production cost was reduced from 15.4 euros/kg ($18.5/kg) to 2.9 euros/kg ($3.5/kg) when the production capacity was increased from 30 to 900 kg/d. An economic analysis revealed a 3.5-fold increase in production cost compared with the corresponding production cost of the wet product, with an added value of up to 10.8 x 10(9) euros ($13.0 x 10(9)) within the European Union.

Preparation of prolonged release clarithromycin microparticles for oral use and their in vitro evaluation.

Prolonged release microparticles of clarithromycin (CL) were prepared using Eudragit RL 100 and RS 100 by spray-drying and casting-drying techniques. For the characterization of those microparticles, preparation yield, particle size distribution, X-ray diffraction, thermal behavior, active agent content and in vitro dissolution from the microparticles were performed. HPLC was used for the assay of clarithromycin and the assay method was validated. All the formulations obtained showed prolonged release when compared to pure clarithromycin. Microparticles prepared by spray-drying method had a slower release compared to those of casting-drying method. Spray-drying method seems to be a more suitable method to prepare microparticles for prolongation in release.

A simple, low-cost device for processing and embedding tissues at sub-zero temperatures.

A simple apparatus to maintain tissues samples at sub-zero temperatures during dehydration, infiltration, and polymerization is described. The device uses a conventional siphon-type carbon dioxide gas cylinder to maintain an aluminum block at temperatures as low as -35 degrees C for over 15 hours/cylinder.

Parameters to consider in the selection and purchase of a freeze-drying system.

When considering the purchase of a freeze-dryer, the user must establish his own performance standards and particular requirements for the following reasons: 1. Large monetary investment required for the purchase, operation and maintenance of the equipment. 2. The expense and stability of the products to be freeze-dried. Some of the basic parameters that must be considered: 1. Product requirements, such as volumes, optimum temperature, and vacuum limits. 2. Facility restraints relating to the availability of space, and utilities. 3. Return on the capital investment (ROI) 4. Technical competence of operating and maintenance personnel. When the parameters are established, the buyer is prepared to purchase a freeze-dryer to best suit his needs. Precise cycle development, reliable hardware and personnel training, assure productivity and product quality.

Optimization in freeze-drying.

The author assumes that success in freeze-drying must be judged in economic terms. Following a summary of the reasons given for adopting freeze-drying, and an historical outline to explain the changing emphasis in the performance requirements of equipment, desirable features in design and operation are reviewed as the basis for a charter for plant manufacturers and an aid to comparison between different types of plant. Ways of appraising value for money are examined and a novel method is proposed for maximizing throughput by optimising the conditions in the freeze-dryer.