Freeze-drying Conditions Research Articles

Optimization of Intensification of Freeze-Drying Rate of Banana: Combined Applications of IR Radiation and Cryogenic Freezing

A programmed experimental study on infrared (IR) aided freeze-drying of cryogenically (LN2) frozen heat sensitive material viz. banana (Musa acuminata) rendered faster moisture separation rate compared to the conventionally frozen samples. Response surface methodology (RSM) could determine the simultaneous optimal freeze-drying conditions of 59.78°C IR temperature, 10 mm sample thickness, and 5 h drying time corresponding to the minimum moisture content of 4.11%, lowest final product temperature of 22.799°C, and maximum rehydration ratio of 1.72. Color difference, shrinkage, microstructure, pH, wettability, polysaccharide, and mineral contents of the cryogenically frozen freeze-dried banana at the optimal conditions have been determined coupled with Fourier Transform Infrared Spectroscopy (FTIR) and Carbon Hydrogen Nitrogen Sulfur (CHNS) analyses. Freeze-drying kinetics at optimal conditions have been evaluated and compared with literature published models and the “Handerson and Pabis” model was found to characterize the present case most closely among all drying models. A novel method for intensification of moisture separation rate leading to freeze-dried banana with high quality could thus be explored.

Freeze-drying for controlled nanoparticle distribution in Co/SiO2 Fischer–Tropsch catalysts

Controlling the nanoparticle distribution over a support is considered essential to arrive at more stable catalysts. By developing a novel freeze-drying method, the nanoparticle distribution was successfully manipulated for the preparation of Co/SiO2 Fischer–Tropsch catalysts using a commercial silica-gel support. After loading the precursor via a solution impregnation or melt infiltration, differential scanning calorimetry was used to study the phase behavior of the confined cobalt nitrate precursor phases to ascertain suitable freeze-drying conditions. When a conventional drying treatment was utilized, catalysts showed inhomogeneous cobalt distributions, with 6–8nm nanoparticles grouped in clusters of up to 400nm. In contrast, by utilizing freeze-drying starting at liquid nitrogen temperatures, homogeneous distributions of 4–7nm nanoparticles were obtained. Raising the temperature at which the freeze-drying process takes place resulted in either uniform or strongly non-uniform nanoparticle distributions, depending on the specific conditions and precursor loading method. After reduction, all catalysts showed high activity for the Fischer–Tropsch reaction at 1bar. The catalysts thus synthesized form an excellent platform for future studies of the stability under industrially relevant Fischer–Tropsch conditions.

Novel contact ultrasound system for the accelerated freeze-drying of vegetables

Abstract A contact ultrasound system for the integration into freeze-drying processes for vegetables was developed and process parameters were estimated. Red bell pepper cubes were freeze-dried on a stainless steel screen used as the sound transmitting surface. Ultrasound induced heating effects due to attenuation and absorption in the product and relevant process parameters were investigated. Continuous ultrasound application at an excitation amplitude of 6.7 μm resulted in immediate sample heating at reduced ambient pressure and a loss of freeze-drying conditions. A reduction of the excitation amplitude to 4.9 μm and of the net sonication time to 10% by applying an intermittent treatment with an interval of 10 s ultrasound and 90 s recovery phase allowed freeze-drying at increased sublimation rates without causing sample heating for 7 h of freeze-drying. As drying proceeds less sublimation energy is required in the process and sound energy was partially transformed into heat, which could be used for accelerated moisture removal during secondary drying in combination with further ultrasound effects improving heat and mass transfer (moisture migration, effect on boundary layers, improved evaporation at low pressure cycles). The ultrasound treatment reduced the drying time required to reach a final moisture content of 10% d.b. by 11.5%. The ultrasound treatment did not affect product quality in terms of bulk density, color, ascorbic acid content, and rehydration characteristics. Industrial relevance : Freeze-drying is a unique drying process for the production of high quality food products. However, high energy requirements for sublimation and vacuum generation turn it into a very cost intensive treatment. Current technologies used for the improvement of drying rates (heated plates, infrared radiation, microwave application) are limited to heating effects and can easily impair product quality. In this study a contact ultrasound treatment has been developed close to industrial freeze-drying, where the product is dried on trays. Ultrasound combines the positive effects of heating due to attenuation and adsorption with mechanical effects of pressure waves to improve drying rates and can thus be used to shorten drying times and has the potential to reduce related processing costs.

Structural Properties of Dried Potatoes, Mushrooms, and Strawberries as a Function of Freeze-Drying Pressure

The structural and thermophysical properties of freeze-dried agricultural products (potatoes, mushrooms, and strawberries) were investigated to determine whether these properties were affected by freeze drying conditions. The true density of freeze-dried products was measured with a helium stereopycnometer, and apparent density was obtained by measuring their geometric characteristics. Porosity and pore size distribution were also measured with a mercury porosimeter. The mechanical properties of freeze-dried agricultural products were obtained using a universal testing machine. Dried products were equilibrated in saturated salt solutions of constant water activity and scanned with a differential scanning calorimeter (DSC) for the evaluation of glass transition temperature. Simple mathematical models were developed in order to correlate the structural and mechanical properties with process conditions. The apparent density and mechanical properties of freeze-dried products increased with the applied freeze-...

Optimization of Freeze Drying Conditions for Purified Pectinase from Mango (Mangifera indica cv. Chokanan) Peel

Response surface methodology (RSM) along with central composite design (CCD) was applied to optimize the freeze drying conditions for purified pectinase from mango (Mangifera indica cv. Chokanan) peel. The effect of pectinase content (−2.66, 62.66 mg/mL), Arabic gum (−1.21, 10.21%, w/v), and maltodextrin (0.73, 7.26%, w/v) as independent variables on activity, yield, and storage stability of freeze-dried enzyme was evaluated. Storage stability of pectinase was investigated after one week at 4 °C and yield percentage of the enzyme after encapsulation was also determined. The independent variables had the most significant (p < 0.05) effect on pectinase activity and yield of the enzyme. It was observed that the interaction effect of Arabic gum and maltodextrin improved the enzymatic properties of freeze-dried pectinase. The optimal conditions for freeze-dried pectinase from mango peel were obtained using 30 mg/mL of pectinase content, 4.5 (%, w/v) of Arabic gum, and 4 (%, w/v) of maltodextrin. Under these conditions, the maximum activity (11.12 U/mL), yield (86.4%) and storage stability (84.2%) of encapsulated pectinase were achieved.

Freeze-drying of nanostructure lipid carriers by different carbohydrate polymers used as cryoprotectants

Freeze-drying technique preserves the stability of nanoparticles. The objective of this study was optimization of freeze-drying condition of nano lipid carriers (NLCs). NLCs were prepared by emulsion-solvent evaporation followed by ultra-sonication method. Different carbohydrate and polymeric cryoprotectants including Microcelac® (mixture of lactose and Avicel), Avicel PH102 (microcrystalline cellulose), mannitol, sucrose, Avicel RC591 (mixture of microcrystalline cellulose and sodium carboxymethyl cellulose), maltodextrine, Aerosil and PEG4000 were tested initially. The NLCs showing lower particle size growth and greater absolute zeta potential after freeze drying were chosen for further investigation using Taguchi optimization method. Studied factors included cryoprotectant type and concentration, freezing temperatures applied at different time periods and sublimation time. Sucrose, Avicel RC591 and Aerosil were selected as cryoprotectants from initial screening tests. Increasing their concentration increased the particle size. 1% of Avicel RC591, 24h of freezing at −70°C and 48h sublimation time showed lower growth in particle size.

Optimization of a process to obtain selenium-enriched freeze-dried broccoli with high antioxidant properties

Broccoli exhibits a high content of antioxidant and anticarcinogenic compounds, such as polyphenols and selenium. Since it is mostly consumed as a processed food, elucidating the processing conditions that minimize nutritional losses becomes relevant. The process composed of a blanching step followed by freeze-drying of selenium-enriched broccoli was optimized, in order to maximize the content of Se-methyl selenocysteine (SMSeC), total polyphenols content and anti-radical power (ARP). The optimal blanching conditions agreed for the three responses, and were immersion in water at 72 °C during 1 min. The optimal freeze-drying conditions were slow freezing rate, atmospheric pressure (96.13 kPa), and application of infrared radiation (IR). These conditions allowed keeping 25% ARP, 18% polyphenols content and 174% SMSeC compared to the fresh vegetable. These results will help in establishing the most adequate processing conditions that allow keeping the functional properties of broccoli as a processed food.

Plant expression, lyophilisation and storage of HBV medium and large surface antigens for a prototype oral vaccine formulation.

Current immunisation programmes against hepatitis B virus (HBV) increasingly often involve novel tri-component vaccines containing—together with the small (S-HBsAg)—also medium and large surface antigens of HBV (M- and L-HBsAg). Plants producing all HBsAg proteins can be a source of components for a potential oral ‘triple’ anti-HBV vaccine. The objective of the presented research was to study the potential of M/L-HBsAg expression in leaf tissue and conditions of its processing for a prototype oral vaccine. Tobacco and lettuce carrying M- or L-HBsAg genes and resistant to the herbicide glufosinate were engineered and integration of the transgenes was verified by PCR and Southern hybridizations. M- and L-HBsAg expression was confirmed by Western blot and assayed by ELISA at the level of micrograms per g of fresh weight. The antigens displayed a common S domain and characteristic domains preS2 and preS1 and were assembled into virus-like particles (VLPs). Leaf tissues containing M- and L-HBsAg were lyophilised to produce a starting material of an orally administered vaccine formula. The antigens were distinctly sensitive to freeze-drying conditions and storage temperature, in the aspect of stability of S and preS domains and formation of multimeric particles. Efficiency of lyophilisation and storage depended also on the initial antigen content in plant tissue, yet M-HBsAg appeared to be approximately 1.5–2 times more stable than L-HBsAg. The results of the study provide indications concerning the preparation of two other constituents, next to S-HBsAg, for a plant-derived prototype oral tri-component vaccine against hepatitis B.Electronic supplementary materialThe online version of this article (doi:10.1007/s00299-011-1223-7) contains supplementary material, which is available to authorized users.

Formulation of LDL Targeted Nanostructured Lipid Carriers Loaded with Paclitaxel: A Detailed Study of Preparation, Freeze Drying Condition, and In Vitro Cytotoxicity

In the present study, cholesterol nanostructured lipid carriers with various oleic acid content loaded with paclitaxel (PTX) were prepared by solvent emulsification‐diffusion method using a Taguchi design. Size, zeta potential, entrapment efficiency, drug loading, and release percent of NLCs were measured. The results indicated that the most effective factors on the size were oleic acid content and surfactant percent. Zeta potential was more affected by the drug content. Drug to‐ lipid weight ratio was the most effective factor on entrapment efficiency and drug release from NLC. In the present work, the effect of lyophilization on the particle size and release properties of NLCs was also evaluated. The results revealed no differences between the characteristics of NLCs before and after freeze drying by using 25% w/w sorbitol as cryoprotectant. Cytotoxicity studies indicate that PTX associated with the NLC is also effective in HT‐29 cell lines and enters the cancer cells selectively through the LDL receptor endocytic pathway. The IC50 values of free PTX solubilized in Cremophor EL and NLC‐born PTX after 72 h exposure were 8.32 ± 1.35 ng/mL and 5.24 ± 0.96 ng/mL, respectively.

Preservation of functionality of Bifidobacterium animalis subsp. lactis INL1 after incorporation of freeze-dried cells into different food matrices

The aim of this work was to investigate how production and freeze-drying conditions of Bifidobacterium animalis subsp. lactis INL1, a probiotic strain isolated from breast milk, affected its survival and resistance to simulated gastric digestion during storage in food matrices. The determination of the resistance of bifidobacteria to simulated gastric digestion was useful for unveiling differences in cell sensitivity to varying conditions during biomass production, freeze-drying and incorporation of the strain into food products. These findings show that bifidobacteria can become sensitive to technological variables (biomass production, freeze-drying and the food matrix) without this fact being evidenced by plate counts.

Effect of Drying Methods on the Quality of the Essential Oil of Spearmint Leaves (Mentha spicata L.)

Drying is one of the primary processes involved in the manufacture of herbs, which themselves come in the form of stems, leaves, and roots. The quality of the final product depends on the procedure used and drying method. This article presents the results pertaining to the drying behavior of spearmint in both hot air drying and freeze drying conditions. Conventionally, herbs are dried at high temperatures (40–45°C), which results in a deterioration of product quality. The characteristics of vacuum freeze–dried herbs were studied, and the quality of the freeze-dried products was assessed. It was found that drying time and essential oil content were strongly influenced by chamber pressure. Higher chamber pressure tended to lengthen the drying time but preserved the major volatile compounds of spearmint in the final product. The quality of the freeze-dried product was assessed as being lower than that of the raw material but higher than that of a convectively dried product. Four different mathematical models were fitted to the drying data. A water absorption test confirmed that the rehydration ratios of vacuum freeze–dried mint leaves were higher than those that were convectively dried.

Prediction of optimal conditions of infrared assisted freeze-drying of aloe vera ( Aloe barbadensis) using response surface methodology

The present study illustrates an extensive experimental study on infrared (IR) assisted freeze-drying of aloe vera ( Aloe barbadensis) coupled with statistical analysis. A ‘three parameter three level’ face centered central composite design (FCCD) has been employed to develop multivariate regression models in order to evaluate the influence of process parameters on the quality of the freeze-dried aloe vera powder. Optimal freeze-drying conditions of 8.5 W/g IR power, 80.24 °C product temperature and 6.67 h drying time have been established corresponding to minimum moisture content of 3.49%, maximum wettability of 52.84 s and maximum yield percent of 3.87 through response surface methodology (RSM). Separate validation experiments at the derived optimal conditions ascertained the predictive ability of the developed model equations. The outcome of this study would contribute to development of technical capabilities for the design of freeze-driers applicable to such high valued medicinal herbs.

Physiologically Stressed Cells of Fluorescent Pseudomonas EKi as Better Option for Bioformulation Development for Management of Charcoal Rot Caused by Macrophomina phaseolina in Field Conditions

Bioformulation that supports the inoculant under storage condition and on application to field is of prime importance for agroindustry. Pseudomonas strain EKi having biocontrol activity against Macrophomina phaseolina was used in the study. EKi cells were pretreated by carbon starvation, osmotic stress (NaCl), and freeze drying conditions, and talc-based bioformulation was developed. Combined pretreatment with carbon starvation and osmotic stress was given to Pseudomonas cells. Bioformulation of untreated, freeze dried (FD), carbon starved, osmotic stressed, and combined pre-treated cells showed 50.36, 44.76, 45.95, 34.82, and 27.27% reduction in CFU counts after 6 months of storage. The osmotic stressed cells showed one over-expressed protein (11.5 kDa) in common with carbon starved cells responsible for its better shelf life. The plant growth promotory activity of bioformulations was determined taking Cicer arietinum as a test crop in M. phaseolina infested field. Carbon starved + osmotic stressed cells showed maximum enhancement of dry weight (272.56%) followed by osmotic stressed (230.74%), untreated (155.70%), FD (88.93%), and carbon starved (59.34%) cells over uninoculated control. Carbon starved + osmotic stressed, osmotic stressed, untreated, FD, and carbon starved cells showed 156.60, 100, 75, 40, and 16.67% reduction of charcoal rot disease over uninoculated control. The results clearly showed that combined pretreatment by carbon starvation and osmotic stress provides the bacteria potential of rapid adaptation to different environment conditions.

The influence of freeze drying conditions on microstructural changes of food products

The drying of food products can result in significant changes in the chemical composition, morphology and physical properties of foods and can lead to stabilized products with longer shelf-life and easier commercialization. Information on porous structure of foods is very important, characterizing the quality and texture of dehydrated food products. Therefore, structural properties, such as porosity, bulk density and true density of freeze-dried food products were investigated as affected by process conditions. Rice kernels were boiled for different time periods and agricultural products, including potato, mushroom and strawberry, were cut into cubes. The samples were frozen, tempered in liquid N2 and freeze-dried, under various vacuum conditions, using a laboratory freeze-dryer. True density of the products was measured using a helium stereo-pycnometer. Bulk density was obtained by measuring the dimensions of the samples with a Vernier caliper. Simple mathematical models were developed in order to correlate the structural properties with process conditions. The microstructure of food products was also analyzed by Scanning Electron Microscopy and image analysis. Bulk density of freeze-dried materials increased with the applied pressure during freeze-drying, while porosity decreased. In addition, bulk density of freeze-dried rice kernels decreased with the increment of boiling time, while porosity increased. The changes in bulk density and porosity were closely supported by microstructural observations, according to SEM images. The microstructural changes of products, freeze-dried under various vacuum conditions, can be predicted using the proposed models and image analysis.

Comparative Study of Different Process Conditions of Freeze Drying of ‘Murtilla’ Berry

Different operating conditions for drying halves of ‘Murtilla’, a native Chilean berry food species, were studied in atmospheric freeze drying, using dry air through a pulsed fluidized bed, and vacuum freeze drying. Applying a 23 experimental design, the effect of the freezing rate, the air temperature, and the application of infrared radiation was studied on the moisture content and the drying time. Fast freezing with infrared (IR) and air at 15°C for the second drying stage allowed achieving final moisture contents similar to vacuum freeze drying in equivalent total drying periods. Drying at the same conditions except with air at 5°C resulted in a larger preservation of antioxidant capacity of the fresh fruit. Also, the texture was adequate for a dry fruit, with a pleasant flavor for direct consumption or mixed with yogurt. The drying kinetics of the first drying stage was modeled by an equation based on the uniformly retreating ice front model, which gave a reasonable description of the trend for this stage, although it does not include the application of IR radiations or the rate of freezing. The Page equation was an adequate tool to represent the second drying stage (which started after 7 h) for each experimental run, by using specific parameters (n and k) obtained by fitting the experimental data. The parameters exhibited similar values to those cited in the literature for foods.

Optimization of freeze-drying condition of amikacin solid lipid nanoparticles using D-optimal experimental design

Amikacin as an aminoglycoside antibiotic was chosen to be loaded in a cholesterol carrier with nanoparticle size and sustained release profile to increase the dose interval of amikacin and reduce side-effects. To support the stability of solid lipid nanoparticles (SLNs), freeze-drying was suggested. Factors affecting the freeze-drying process in the present study included the type and concentration of cryoprotectants. Pre-freezing temperature effects were also studied on particle size of SLNs of amikacin. In some preliminary experiments, important factors which influenced the particle size of SLNs after lyophilization were selected and a D-optimal design was applied to optimize the freeze-drying conditions in the production of SLNs with minimum particle size growth after freeze-drying. Zeta potential, DSC thermograms, release profiles and morphology of the optimized particles were studied before and after freeze-drying. Results showed sucrose changed the particle size of SLNs of amikacin from 149 ± 4 nm to 23.9 ± 16.7 nm; in that situation, the absolute value of zeta potential changed from 1 ± 0.7 mV to 13 ± 4 mV. The release profiles showed a sustained release behavior of the loaded drug that did not change significantly before and after freeze-drying, but a burst effect was seen after it in the first 2 h. DSC analysis showed chemical interaction between amikacin and cholesterol.

Effect of culture age, protectants, and initial cell concentration on viability of freeze-dried cells ofMetschnikowia pulcherrima

The effect of freeze-drying using different lyoprotectants at different concentrations on the viability and biocontrol efficacy of Metschnikowia pulcherrima was evaluated. The effects of initial yeast cell concentration and culture age on viability were also considered. Yeast cells grown for 36 h were more resistant to freeze-drying than were 48 h cells. An initial concentration of 10⁸ cells·mL⁻¹ favoured the highest survival after freeze-drying. When maltose (25%, m/v) was used as protectant, a high cell viability was obtained (64.2%). Cells maintained a high viability after 6 months of storage at 4 °C. The biocontrol efficacy of freeze-dried cells was similar to the activity of fresh cells on 'Gala' apples and was slightly lower on 'Golden Delicious' apples. After optimizing freeze-drying conditions, the viability of M. pulcherrima cells was similar to that obtained in other studies. The results constitute a first step towards the commercial development of M. pulcherrima as a biocontrol agent.

Nanoparticle-Based Surface Templating

This study is focused on making molds with micrometer-sized feature arrays, studying high solids loading nanoparticle suspension for nanoparticle-based templating, and cast forming of surface-templated materials. Polydimethylsiloxane (PDMS) and silicone molds with micrometer-sized feature arrays are made using mold cores templated by a focused ion beam microscope. Al2O3 nanoparticle suspensions are evaluated based on nanoparticle interaction energy and suspension flowability in order to obtain stable and high solids loading suspensions. Templated feature transfer ability is compared for the PDMS and silicon molds under ambient and freeze-drying conditions. This work provides a new approach for surface templating of nanoparticle-based materials.

Preparation and characterization of medium-chain fatty acid liposomes by lyophilization

In this study, medium-chain fatty acid (MCFA) liposomes were prepared by the film ultrasonic dispersion, modified ethanol injection, and reverse-phase evaporate methods. The results indicated that the liposomes prepared by the thin-film ultrasonic dispersion method had a high entrapment efficiency of 82.7% and a good distribution in size diameters. The MCFA liposomes were freeze-dried and the optimal preparation conditions of freeze-drying were as follows: The cryoprotectants were mannitol and sucrose (1:1 w/w), the hydrated medium was distilled water, and the freeze-drying time was 48 hours. Under these conditions, the freeze-dried MCFA liposomes had a perfect appearance, a small particle size, and high encapsulation efficiency. The mean diameters were 251.1 and 265.3 nm, and the encapsulation efficiencies were 80.5 and 79.2% for freshly prepared and reconstituted liposomes, respectively.

Fabrication of pulverized cellulosics by ultra high-pressure water jet treatment and usage in polymer nanocomposites and graft copolymerization

Cellulose powders were pulverized by an ultra high-pressure counter-collision treatment in an aqueous suspension state, and then used in composites with vinyl polymers and graft copolymerized with methyl methacrylate using ceric ion initiator. The influence of freeze-drying methods after microfibrillation of cellulose was visualized by scanning electron microscopy (SEM). The coalescence of microfibrillar structures was observed to increase easily reflecting the freeze-drying conditions. While the degree of microfibrillation was unsatisfactory for use as fillers in preparing polymer-nanocellulose composites, the situation was found to be rectified with the use of a proper kneading technique. The roles of microfibrillated cellulose in processes producing bio-nano-composites suitable for practical uses were studied through SEM observations and measurements of physical properties. The characteristics of the successive graft copolymerization were studied through examining the monomer conversion and the grafting effi- ciency. The significant improvement in the grafting became apparent in response to the counter-collision pretreatment. Dynamic viscoelastic properties of the molded sheets of the grafted products were studied to measure the effects of the graft copolymerization compared with the corresponding physically blended material and neat poly(methyl methacrylate). The grafting reaction resulted in composites with much higher heat-resisting properties than those obtained for the latter two.