Effect of a High-Pressure-Induced Freezing Process on the Stability of Freeze-Dried Nanocapsules

The objective of this study was to develop a freeze-drying process involving high-pressure techniques during freezing in order to optimize the stability of nanocapsules. Nanocapsules prepared by the emulsion-diffusion method were frozen at ? 20, ? 10, and ? 5°C, respectively, and dried under vacuum as a conventional freeze drying (CFd). For the high-pressure freezing process, the nanocapsules suspensions were frozen at ? 20, ? 10, and ? 5°C at 100, 200, and 300 MPa, respectively, and then dried under vacuum conditions (abbreviated as HPFd). The size and morphological analysis of freeze-dried samples were investigated by using Mastersizer®, TEM, and SEM. From these experiments, the mean nanocapsules sizes were entirely aggregated depending on increasing pressure and decreasing freezing temperature in CFd. In HPFd, the nanocapsules frozen at ? 10°C were stable depending on the increment of the pressure level. We concluded that the HPFd process was more effective for the stability of nanocapsules compared to the CFd process at freezing temperatures of ? 10°C due to high supercooling of the internal phase during the high-pressure freezing process.     

The role of drying methods on enzymatic activity and phenolics content of impregnated dried apple

Infusion of antioxidants into vegetables is a new food strategy managed by matrix processing. Raw and blanched apple were air- or freeze-dried. In the case of freeze-dried samples, different freezing methods were previously applied: conventional (?28°C), blast freezing (?30°C), and liquid N₂ (?196°C). Afterwards, air- and freeze-dried samples at different conditions were impregnated with a concentrated (40°Brix) tea extract and finally, air-dried for their stabilization. Total phenolic content (TPC), antioxidant capacity (AC), enzymatic activity, and microstructure were analyzed. Regardless of pretreatments, the impregnation and the further drying improved the antioxidant potential. Samples with the most porous microstructure free of degradative enzymes provided high AC (78.5?±?0.9?mg Trolox/g dried matter) and TPC (16.7?±?0.2?mg GAE/g dried matter).     

A Review of: “FLUIDIZATION VI” Editors: J.R. Grace,L.W. Shemilt and M.A. Bergougnou Publisher: AIChE (for Engineering Foundation) 345 East 47th St., New York,N.Y. 10017, 1989, 750 p.

ABSTRACT

Heat pumps in combination with fluidized bed driers have been investigated extensively at The Norwegian Institute of Technology. A laboratory plant was constructed and a series of experiments on different types of temperature sensitive products were executed. By using heat pump, good temperature and humidity regulation is achieved. Drying temperatures can be regulated from ?20°C to 50°C. This gives the possibility of freeze-drying at atmospheric pressure, and drying at temperatures above 0°C in the same plant. By using a temperature program, including an initial period of freeze drying, it is possible to regulate the products' physical properties. Examples are: the sinking velocity of fish fry feed, rehydration ability, colour and taste of dried fish, meat and vegetable products. Further, biotechnological products like bacterial cells and biomolecules/enzymes were dried with improved biological activity of the products compared to traditional drying methods like vacuum freeze drying or spray drying.     

Physicothermal Properties of Freeze-Dried Fish Oil Nanocapsules Frozen under Different Conditions

This research compared the effects of vacuum freeze drying (VFD) and conventional freeze drying (CFD) processes on the stability of fish oil–loaded nanocapsules (NCs). For CFD, the NCs showed aggregation that was dependent on the freezing temperature. The encapsulation efficiency of CFD was greater than that of VFD, except at the freezing temperature of ?30°C. From differential scanning calorimetry (DSC) analysis and scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images, it was concluded that the CFD process was more effective in the oxidative stability of the fish oil–loaded NCs. In addition, the vacuum-freezing process may affect the fragility of the poly-?-caprolactone membrane due to its low encapsulation efficiency and aggregation of particles. No differences in Z-potential values between the CFD samples were observed, whereas in the VFD samples, it became increased in the negative charge when decreasing the cooling temperature of the fish oil–loaded nanocapsules for the freeze-drying procedure. Regarding the observation of surface tension, CFD samples presented lower values than VFD samples at given freezing temperature.     

Cracking during freeze-drying in dense freeze cast ceramics: Role of drying rate

Cracks can form during the freeze-drying of freeze cast ceramic suspensions while attempting to produce dense ceramics. The suspensions contain alumina particles dispersed in cyclohexane. The rate of drying is controlled by the pressure and temperature during drying (slow drying at atmospheric pressure and −15°C and fast drying under vacuum while the temperature slowly increases from −80°C to room temperature). X-Ray micro-computed tomography was used to characterize internal crack formation. Cracks were found to occur during freeze-drying rather than during freezing. Both slow and fast drying produced cracks, although two different morphologies were observed. Mechanistic models are proposed for the formation of both types of cracks. The rate of freezing was found to influence the formation of cracks. Slow freezing tended to reduce the formation of drying cracks because the slower freezing produced a more heterogeneous distribution of particles and porous regions, which tends to allow stress to be relieved by opening up existing pores rather than forming cracks in the more homogeneous fast frozen bodies.     

Effect of blanching on volatile compounds and structural aspects of Cordyceps militaris dried by microwave-assisted pulse-spouted bed freeze-drying (MPSFD)

Effect of low temperature blanching at 50°C (for 15, 30, and 60?min) and high temperature blanching at 100°C (30, 60, and 120?s) on volatile compounds and structural properties of Cordyceps militaris dried by microwave-assisted pulse-spouted bed freeze-drying were investigated. A total of 83 volatile compounds were identified. Blanching at 100°C remarkably decreased the ketones and alcohols while contributed to the formation of alkanes. The absence at 993?cm^?1 and the appearance near 1548?cm^?1 in samples blanched at 100°C were observed, indicating blanching at high temperature would cause the loss of polysaccharides and the degradation of proteins. Principal component analysis and cluster analysis suggested that volatile compounds in untreated samples and those blanched at 50°C for 15?min were similar. In general, blanching at 50°C for 15?min is recommended regarding the retention of flavor components and structural properties of dried C. militaris.     

Control of pore channel size during freeze casting of porous YSZ ceramics with unidirectionally aligned channels using different freezing temperatures

Porous yttria-stabilized zirconia (YSZ) ceramics with unidirectionally aligned pore channels were prepared by freezing YSZ/tert-butyl alcohol (TBA) slurry under different freezing temperatures of ?30, ?78 and ?196 °C, respectively. After removing the frozen TBA via freeze-drying in vacuum at ?50 °C, the green samples were sintered at 1450 °C for 2 h in air. The results showed that the freezing temperature significantly influenced microstructure and properties of the porous YSZ ceramics. Both microstructure observation and pore size distribution indicated that the pore channel size decreased significantly with decreasing freezing temperature, regardless of microstructure variations in the individual sample. Both porosity and room-temperature thermal conductivity of the porous YSZ ceramics varied under different freezing temperatures. Regardless of microstructure variations in the samples under different freezing temperatures, all samples had unidirectional pore channels with increasing pore channel size along the freezing direction. The fabricated samples had remarkably low thermal conductivities both in directions perpendicular and parallel to the channel direction, thus rendering them suitable for applications in thermal insulations.     

Drying of Seabuckthorn (Hippophae rhamnoides L.) Berry: Impact of Dehydration Methods on Kinetics and Quality

Convective hot air drying and freeze drying were investigated as potential dehydration processes to obtain powders of seabuckthorn fruit pulp. Halved seabuckthorn fruits were placed in a hot air dryer and dried at 1 m/s and at 50 or 60°C or freeze dried at less than 30 mTorr and at 20 or 50°C shelf plate temperature. An initial characterization of the seabuckthorn pulp (moisture, pH, soluble solid content, vitamins C and E, total phenolics, and carotenoids) was performed. Water loss, total phenolic compounds, total carotenoids, and vitamin C were determined at different processing times. Vitamin E was determined before and at the end of drying.

Freeze-drying kinetics were faster than air drying, probably due to lower moisture diffusion in the compact, sugary, and oily structure of the air-dried tissue. The temperature had an important impact on hot air–drying and freeze-drying kinetics. Drying method and processing times affected the remaining phenolic, carotenoid, and vitamin contents of seabuckthorn berries. Freeze drying was revealed as a superior method to obtain seabuckthorn powders because of the lower residual moisture content, the ease of grinding, as well as the better nutritional retention.     

The effect of freezing on the hot air and microwave vacuum drying kinetics and texture of whole cranberries

Abstract

The aim of this study was to evaluate the effect of convective and cryogenic freezing, hot air convective drying (HACD) at 60, 70, 80, and 90?°C and microwave vacuum drying (MWVD) at 100, 150, 200, 300, 450, and 500?W on the drying kinetics and texture of whole cranberries. Effective moisture diffusivities and drying rates were higher, whereas drying times were shorter for the samples dried by MWVD compared with the samples processed by HACD. The drying kinetics of cranberries during MWVD was discussed based on the hypothesis postulating that changes in the drying rate of cranberries during MWVD can be explained by and correlated with changes in the pressure gradient on material surface. Cranberries processed by MWVD were characterized by significantly greater hardness, gumminess, and chewiness in comparison with HACD samples. MWVD was found to be an effective method for producing dried snacks characterized by hard and crispy texture and considerable resistance to stress associated with manufacturing, packaging, storage, and delivery. HACD produced brittle fruit that were difficult to store and transport and were not fully suitable for direct consumption. Convective freezing before MWVD improved the overall appearance of cranberries, whereas cryogenic freezing combined with high temperature HACD adversely influenced the drying rate and produced dried cranberries with suboptimal overall appearance.     

Optimization of primary freeze drying conditions for powdered chicken meat hydrolysate from mechanically deboned chicken residues

Abstract

In this study, mechanically deboned chicken meat residues were hydrolyzed by protease enzyme and chicken meat hydrolyzate was freeze-dried in order to produce high-quality meat powder. Due to its high cost, energy and time consumption, freeze-drying conditions needed to be optimized. Response surface methodology was used for optimization with the independent variables shelf temperature, lyophilization temperature and freezing rate. The responses were sublimation time, solubility and in vitro protein digestibility. The optimum conditions were shelf temperature, 15?°C; lyophilization temperature, –10?°C; and freezing rate, 2.0?°C/min. Sublimation time, solubility and in vitro protein digestibility for this optimum conditions were found to be 590.344?min, 25.626% and 23.808%, respectively.     

Effects of drying conditions on physicochemical and antioxidant properties of banana (Musa cavendish) peels

A significant amount of banana peels is generated as waste annually and shows great potential as a lead material for further utilization in the nutraceutical industry. However, potentiality of banana peel utilization largely depends on the favorable drying condition of the material before it can be used for further processing. Therefore, it is necessary to identify the suitable drying conditions for banana peel. This study investigated the effect of six different drying methods on the quality of banana peels. The results showed that different drying conditions significantly affected the physical, chemical, and antioxidant properties of dried peels. Microwave irradiation at the power level of 960?W for 6?min was the most suitable condition, as these dried peels had good physical properties, minimum loss of bioactive compounds, and antioxidant properties. This was followed by freeze-drying, vacuum oven at 60°C, hot air oven at 120°C, dehumidified air at 60°C, and sun drying. The peels dried by microwave possessed a total phenolic content of 25.26?mg of gallic acid equivalents/g of dry matter (DM) and potent antioxidant capacity [(1,1-diphenyl-2-picrylhydrazyl) of 37.70; 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid of 46.35; ferric reducing antioxidant power of 45.94; and cupric ion reducing antioxidant capacity of 64.55?mg of trolox equivalents/g of DM]. Therefore, the study recommends the use of microwave irradiation under the studied condition (power level of 960?W for 6?min) for further processing and utilization.     

Pulsed vacuum drying (PVD) technology improves drying efficiency and quality of Poria cubes

The objective of this research was to examine the drying characteristics of pulsed vacuum drying (PVD) system as an alternative drying technology for a functional food—Poria cocos. Poria cubes in thin layer were dried at different temperatures (55, 65, and 75°C), vacuum duration (5, 15, and 25?min), and atmospheric pressure duration (4, 8, and 12?min) to evaluate the operating conditions on the drying kinetics and quality attributes of P. cocos. The quality attributes included volume shrinkage ratio, firmness, water-soluble polysaccharide content. Volume shrinkage ratio was determined by image processing technology and analyzed by Bigot’s curves. The material internal temperature was also recorded during the whole drying process. Considering the drying rate and quality attributes, drying temperature of 65°C, vacuum pressure duration of 15?min, and atmospheric pressure duration of 4?min were proposed as the most favorable drying conditions for drying Poria cubes. The current work indicates PVD is a promising technology for P. cocos drying as it not only enhances the drying process but also improves the quality attributes of it.     

Effect of particle size and freezing conditions on freeze-casted scaffold

Freeze casting is one of the emerging and novel manufacturing routes to fabricate porous scaffolds for various applications including orthopedic implants, drug delivery, energy storing devices etc. Thus, it becomes important to understand this process in a deeper sense. Present work was focused to study the effect/influence of basic parameters, particle sizes, and freezing conditions on the mechanical properties and microstructures of porous scaffold fabricated by freeze casting. β-tricalcium phosphate (β-TCP) and hydroxyapatite (HAp) powder with particle sizes of 10?μm and 20?nm were used. Prepared slurries were freeze casted at constant freezing temperature (5?°C) and constant freezing rate (1.86?°C/min) to study the effect of freezing conditions on mechanical and microstructural properties of the porous scaffold. It was observed that porous scaffold fabricated by nanoparticles has given better porosity (63.22–76.16%), than scaffold fabricated by microparticles (13–43.05%) at given solid loading of both freezing conditions. Although, the range of pore size of the scaffold fabricated by nanoparticles (CFR: 2.60–0.84?μm; CFT: 1.66–0.46?μm) was lower than that of scaffold fabricated by microparticles (CFR: 9.45–4.83?μm; CFT: 4.72–2.84?μm). The compressive strength of scaffolds prepared by nanoparticles was in the range of trabecular bone. Moreover, the results of present work will pave the way for the fabrication of porous scaffold with desired pore size and porosity for various implants, energy, and drug delivery applications.     

Ultrasound-assisted drying of orange peel in atmospheric freeze-dryer and convective dryer operated at moderate temperature

Abstract

Atmospheric freeze-drying (AFD) at ?10?°C and moderate temperature convective drying (MTD) at 50?°C without and with ultrasound application (20.5?kW/m³) were carried out. Alcohol insoluble residue (AIR) and its swelling capacity (SC), water retention capacity (WRC) and fat retention capacity (FRC) were measured in the dried product. Ultrasound significantly shortened the drying time in both processes, the intensification effect being more significant in atmospheric freeze-drying (57% and 27% reduction in atmospheric freeze-drying and convective drying, respectively). As regards AIR and WRC, no effect was observed of either the drying temperature or ultrasound application. On the contrary, SC was significantly lower in AFD samples. The FRC of MTD samples was similar to that of the fresh ones and higher than the values obtained for atmospheric freeze-dried samples. Therefore, convective drying at moderate temperature preserved the AIR properties better than atmospheric freeze-drying.     

Sorption Properties of Vacuum-Dried Strawberries

This work demonstrates the influence of changes in parameters of vacuum drying (temperature and pressure) on the sorption properties of dried strawberries. Fruits were dried at 50 and 70°C under pressures of 4 and 16 kPa. Vacuum drying was also conducted during the first 4 h at 70°C and then the temperature was decreased to 50°C at a pressure of 4 kPa. The other combination included increasing the pressure after the first 4 h from 4 to 16 kPa at a drying temperature of 70°C. Sorption isotherms were determined in the dried strawberries. It was shown that with increasing drying temperatures, there was a notable deterioration in the capacity for absorbing water vapor by the vacuum-dried fruit. On the other hand, the pressure at which vacuum drying proceeded did not significantly affect water vapor absorption. Changing the parameters of vacuum drying—that is, temperature in the range of 50–70°C and pressure in the range of 4–16 kPa—affected the shape and structure of the resultant dried strawberries. The combination of vacuum drying with convective drying also influenced the shape and structure of the dried fruit.     

Freezing as a method of study of early cement paste hydration

A method for studying early stage hydration of cement paste is proposed. The method consists in freezing the specimens at specific times in liquid nitrogen at ?195°C. These are then vacuum dried and studied under scanning electron microscope. By this method the hydration can be stopped at any time and exactly the same structure of hydration products, which was present at the freezing time, can be studied under microscope. It is though that this method can be useful specially to study structure of the fresh cement paste. Chemical reactions (phase identification) in different ceramic materials at various stages may also be studied by this method.     

Design and performance evaluation of a pilot-scale pulsed vacuum infrared drying (PVID) system for drying of berries

Abstract

The objective of current work was to develop a new pilot-scale pulsed vacuum infrared drying (PVID) system for the drying of berries. The system design and drying performance evaluation for grape and goji berries are reported here. The PVID system consisted of three major sections, including infrared heating section, vacuum section, and a controlling section. Electrical infrared (IR) emitter was made with carbon fiber sheet at the thickness of 2–4?mm, which emitted IR wavelength of 1–30?μm. The control system was used to achieve paused pressure by switching the drying chamber pressure between atmospheric pressure (101?kPa) and vacuum (3–10?kPa) successively and maintaining the pressure for different time periods. Grapes and goji berries were dried in a single layer at three different temperatures (55, 65, and 75?°C) with an atmospheric duration ranging from 1 to 12?min and vacuum duration from 10?min to constant vacuum. The drying characteristic and quality of PVID dried berries were investigated and compared with that of hot air (HA) dried berries. Results showed that the IR heating temperature, atmospheric duration, and vacuum duration had significant effects (p?<?.05) on the drying time. The optimum drying conditions for grapes and goji berries were IR heating at 65?°C, vacuum duration of 15?min, and atmospheric duration of 4 and 2?min, respectively. The corresponding drying time is nearly 720?min for grapes, and 450?min for goji berries. The PVID dried grapes and goji berries had more attractive color than that of HA dried ones. These findings demonstrated that PVID should be a promising method to produce high-quality dried berries. This study laid a good foundation for scaling up the technology in the future.     

Drying of Lemon Myrtle (Backhousia citriodora) Leaves: Retention of Volatiles and Color

Lemon myrtle plant (Backhousia citriodora) leaves were dried at three different drying temperature conditions (30, 40, and 50°C) in a fluidized bed dryer. The retention of the principal volatile compound, citral, was analyzed in dried products obtained at these three drying conditions. The changes in the color parameters L?, a?, b? of leaves were also analyzed. More than 90% of citral was retained at 50°C drying temperature, whereas the retention at 30 and 40°C was 81 and 85%, respectively, suggesting that higher temperature is beneficial to achieve higher retention of volatiles. However, in terms of the color, all the color parameters were changed maximum at 50°C drying temperature unfavorably, suggesting that the higher temperature drying causes more degradation of the pigment. Blanching of the leaves in hot water at 80°C for 1 min prior to drying did not result in any improvement in volatile retention or color.     

Optimization of explosion puffing drying for high-value yellow-fleshed peach crisps using response surface methodology

Response surface methodology (RSM) was used to comprehensively evaluate the pilot scale nonfried explosion puffing drying (EPD) conditions for developing high-value yellow-fleshed peach crisps. The independent variables were different levels of vacuum drying temperature, vacuum drying time, and puffing pressure difference. The responses were crispness, total color difference (ΔE), total carotenoid content (TC), and DPPH radical scavenging capability (AEAC). Statistical analysis revealed that vacuum drying temperature significantly affected all the responses, puffing pressure difference showed maximum influences on TC, AEAC, and crispness, while vacuum drying time showed influences on TC and AEAC. The optimum EPD conditions obtained by RSM were vacuum drying temperature, vacuum drying time, and puffing pressure difference of 73?°C, 144?min, and 0.05?MPa, respectively. At this optimal condition, crispness, ΔE, TC, and AEAC value were found to be 7.3?N, 18.3, 53.5?µg/mg d.w., and 865.4?mg AA/100g, respectively. The EPD-dried yellow-fleshed peach crisps contained higher amounts of carotenoids and AEAC values when compared to hot-air dried samples, they were also found to be crispier than vacuum freeze-dried samples.     

Strawberry drying: Development of a closed-cycle modified atmosphere drying system for food products and the performance evaluation of a case study

In the present study, a closed-cycle modified atmosphere drying (CC-MAD) system was developed as an alternative drying technique to facilitate drying processes for agricultural commodities appropriate to highly humid and sunny regions with a better quality. An absorption dehumidifying system was designed for working pseudo-continuously with the most efficient absorbent in terms of moisture absorption, desorption rate, and capacity. The system, assisted by a solar panel for absorbent regeneration, was tested, while its optimum working condition was determined by strawberry drying. This unique process was comparatively carried out using hot-air and freeze-drying techniques in terms of processing time and final product quality. Strawberry slices (5?mm thickness) were dried successfully using CC-MAD. The optimum drying conditions of CC-MAD were determined as drying temperature of 60°C, drying air/gas velocity of 3?m/s and drying medium oxygen level of 9.47%. The loss of ascorbic acid was significantly reduced by CC-MAD technique. These losses were found to be 2.9, 6.9, 27.2, and 23.8% by freeze-drying, CC-MAD, hot-air drying, and hot-air drying combined with CC-MAD, respectively. The total monomeric anthocyanins loss was also significantly reduced by the CC-MAD technique (20.3%), in a similar way to that of freeze-drying (18.1%) in comparison with hot-air drying (40.4%). In addition, CC-MAD (12,446?kJ/kg fresh product at 4?h drying time) is three times more advantageous in terms of energy cost compared with freeze-drying (30492.8?kJ/kg fresh product at 24?h drying time) and six times faster in terms of drying time. This new drying system can be used as an alternative to freeze-drying in the drying of foods, especially in products sensitive to oxidation.