Freeze-drying Time Research Articles

Microwave freeze-drying characteristics and crosslinking behavior of wheat starch-laurel acid complex

This article investigates the effect of different microwave powers on the crosslinking behavior and microwave freeze-drying characteristics of wheat starch-lauroyl arginate complex during the microwave freeze-drying process. During microwave freeze-drying, as microwave power increased from 0.1 W/g to 0.9 W/g, the freeze-drying time of WS-LA was reduced by 50 %, while the uniformity of freeze-drying was not affected by its composition. In the research results obtained from DSC, Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), XRD, and SEM analyses, with the microwave power increased from 0.1 W/g to 0.9 W/g, the enthalpy value of the melting peak of the WS-LA (wheat starch-lauric acid) composite decreased from 1.15 J/g to 0.62 J/g. The full width at half maximum (FWHM) value increased from 25.6 to 30.79. The ratio of absorbance at 1022/995 cm−1 increased from 1.0111 to 1.0707. The recrystallization (RC) value decreased from 8.77 % to 0.07 %. Additionally, in the microstructure, the size of WS-LA composite particles decreased accordingly. The above findings indicated that the increase in microwave power during microwave freeze-drying had a negative impact on the formation of the WS-LA complex and the ordering of its structure in the sample.

Study on Microwave Freeze-Drying of Krill

Antarctic krill (Euphausua superba) need to undergo freeze-drying to facilitate lipid extraction, but freeze-drying is time-consuming and energy-intensive, resulting in high processing costs. Microwave heating technology can reduce freeze-drying time and lower energy consumption costs. The objective of this study was to establish a drying kinetic model to help the microwave freeze-drying process by predicting krill drying time and evaluating the impact of the drying process on krill quality. The results showed that changing the microwave power did not alter the total energy requirement to complete drying when the sample weight was fixed. The total energy requirement for microwave drying increases with the sample weight. Comparing the three methods of freeze-drying (FD), microwave freeze-drying (MWFD), and hot-air drying at 55 °C (HAD) showed that they took 18, 0.67, and 16 h, respectively, to reach the drying endpoint for krill. Overall, HAD resulted in browning, shrinkage, and quality degradation of krill due to its high temperature and long duration. While the appearance and active ingredient contents of FD krill are slightly better than those of MWFD krill, FD requires a longer process and more energy. MWFD can reduce drying time by 20 times and energy consumption by 95% compared to FD.

Examining the Effect of Freezing Temperatures on the Survival Rate of Micro-Encapsulated Probiotic Lactobacillus acidophilus LA5 Using the Flash Freeze-Drying (FFD) Strategy.

This work proposes a novel drying method suitable for probiotic bacteria, called flash freeze-drying (FFD), which consists of a cyclic variation in pressure (up-down) in a very short time and is applied during primary drying. The effects of three FFD temperatures (-25 °C, -15 °C, and -3 °C) on the bacterial survival and water activity of Lactobacillus acidophilus LA5 (LA), previously microencapsulated with calcium alginate and chitosan, were evaluated. The total process time was 900 min, which is 68.75% less than the usual freeze-drying (FD) time of 2880 min. After FFD, LA treated at -25 °C reached a cell viability of 89.94%, which is 2.74% higher than that obtained by FD, as well as a water activity of 0.0522, which is 55% significantly lower than that observed using FD. Likewise, this freezing temperature showed 64.72% cell viability at the end of storage (28 days/20 °C/34% relative humidity). With the experimental data, a useful mathematical model was developed to obtain the optimal FFD operating parameters to achieve the target water content in the final drying.

Optimization of extraction and lyophilization conditions of Feretia apodanthera (Rubiaceae) leaf powders for galenic formulation

Feretia apodanthera (Rubiaceae) is used in traditional medicine for the treatment of various pathologies. Its leaves are chewed and swallowed to treat stomach aches, sleep disorders, etc. With the aim of improving the extraction method in order to obtain high contents of phytochemical compounds and good antioxidant activity, this study aimed to highlight the extraction and lyophilization conditions of two extracts (aqueous and hydro-ethanolic) leaves of Feretia apodanthera.
 An aqueous and hydro-ethanolic extraction was carried out from the leaf powder of Feretia apodanthera, after a maceration plan (mass/volume ratio and extraction time). The extracts obtained were freeze-dried (flask size, filling volume and freeze-drying time) in order to determine the optimal extraction conditions. A phytochemical screening of the extracts with extreme yields of different solvents was carried out by TLC, which led to the determination of certains compounds of interest and the evaluation of the antioxidant activity by the DPPH and FRAP method.
 The optimal maceration conditions were 02 hours and m/V ratio of 1/20 for the aqueous extract and those of the ethanolic extract were 30 min and m/V ratio of 1/20. The optimal freeze-drying conditions were 60h and a 500ml flask 1/3 filled. The presence of flavonoids, tannins, saponosides, coumarins, triterpenes and sterols has been highlighted. The phenolics compounds contents of hydro-ethanolic lyophilisates were higher than those of aqueous lyophilisates. There was no statistical difference between the antioxidant activity of the different extracts.
 The optimal conditions will serve as a standard for the production of the extract necessary for the formulation.
 Keywords : Feretia apodanthera, extraction, freeze-drying, phenolics compounds, antioxidant.

Wave-absorbing material-assisted microwave freeze-drying of initially unsaturated coffee frozen material: Numerical simulation and experimental verification

A multi-physics model of multiphase transport was formulated in describing freeze-drying. Traditional and microwave freeze-drying experiments were conducted using initially saturated and unsaturated coffee materials. The results demonstrated that microwave freeze-drying time of initially unsaturated material assisted by a wave-absorbing material was decreased by 40.4 % compared with traditional freeze-drying time of saturated material. The simulated drying curves achieved excellent agreements with the measured ones. The enhancement mechanisms were analyzed in terms of saturation level, temperature, Darcy’s velocity and energy utilization. Wave-absorbing material-assisted microwave freeze-drying of unsaturated material realized a simultaneous enhancement of mass and heat transfer for the freeze-drying process.

Evaluation of the quality and stability of freeze-dried fruits and vegetables pre-treated by pulsed electric fields (PEF)

This study investigates the application of Pulsed Electric Field (PEF) technology to improve the freeze-drying process, the final product quality and the stability of kiwi fruits, red bell peppers, and red beetroots. Freeze-drying is a fundamental drying technology that aims to maintain the natural attributes of food, but it often leads to challenges such as prolonged drying times and quality degradation. To further understand the implications of applying PEF before freeze-drying, the storage stability of the freeze-dried samples was investigated under both illuminated and dark conditions. PEF treatment was carried out at constant electric field strength of E = 1.0 kV/cm, and specific energy input was varied between 0.2 and 20.8 kJ/kg. This study revealed that PEF treatment significantly decreased the freeze-drying time (2-fold) exclusively for bell peppers. PEF treatment substantially improved volume retention and rehydration capacity for both kiwi fruits and bell peppers, indicating enhanced structural integrity. However, applying PEF had an overall adverse impact on the colour stability of the freeze-dried samples (ΔE > 3). The quality decline was mitigated storing the samples in dark conditions. The results of this study suggest that applying PEF before freeze-drying can represent a promising strategy to enhance the quality of freeze-dried products with improved drying kinetics, volume retention, and rehydration capacity. Careful consideration of storage conditions is essential to prevent the deterioration of product quality over time.

Effects of Freeze-Drying on Sensory Characteristics and Nutrient Composition in Black Currant and Sea Buckthorn Berries

Fresh berries contain numerous components that can undergo complex changes during the drying process. This study aims to investigate the effect of freeze-drying on the sensory and chemical properties of black currant and sea buckthorn berries. Freeze-drying was performed at a shelf temperature of 35–55 °C with a step of 5 °C and durations of 18, 20, 22, and 24 h. Comparing the final freeze-dried berries with their fresh counterparts, it was observed that at a shelf temperature of 50 °C and a drying time of 18 to 20 h, there was a minimal loss in the content of vitamins, organic acids, and carbohydrates. However, based on organoleptic evaluations, the best results were achieved after drying for 20 h. Furthermore, the preservation of citric and malic acids in black currant berries, along with citric, tartaric acids, and sucrose in sea buckthorn berries, was only at 45.6% when the freeze-drying time was extended to 22 h. Considering the physical and chemical properties of listed freeze-dried berries, the optimal parameters were identified as a shelf temperature of 50 °C and a drying time of 20 h. The findings from this study serve as a foundation for selecting appropriate freeze-drying parameters for various types of berries.

Effect of high-voltage electrical discharge (HVED) at high frequency on vacuum freeze-drying time and physicochemical properties of blueberries

Vacuum freeze-drying provides high-quality food products. However, it requires long operating times and high energy consumption. High voltage electrical discharge (HVED) is an emerging technology that could enhance freeze-drying rates and final product quality. This study aimed to evaluate the effect of HVED at high frequency (200 kHz) on freeze-drying kinetics of blueberries (effective moisture diffusivity, drying times) and the physicochemical properties of the resulting freeze-dried fruits. Blueberries were pretreated at different electric field strengths (10, 20, and 30 kV/cm) and operational times (10, 20, and 30 s) and freeze-dried until constant weight. The HVED treatment at 30 kV/cm and 30 s exhibited the best moisture diffusivity values and reduced drying time by at least 30% compared with untreated samples. Samples treated with HVED and freeze-dried preserved their shape and prevented shrinkage. Applying HVED as a pretreatment electrotechnology can help improve the efficiency of freeze-drying and the quality of dried food products.

Effects of osmotic dehydration pre-treatment on process and quality of freeze-dried strawberries (Fragaria x ananassa var. Mencir)

The freeze-drying of fruits is one alternative to increase the added value of fresh fruit, extend the shelf life which the product, and still have properties like fresh fruit. Osmotic dehydration pre-treatment can be applied before drying techniques to produce a new product, maintain nutritional and sensory quality, and improve the drying process. In this research, the effects of osmotic dehydration on freeze-drying performance and the quality characteristics of freeze-dried strawberries were evaluated. Freeze-dried strawberries were made using fresh strawberries without pre-treatments and pre-treatments by osmotic dehydration (OD) with the freeze-drying method. The treatment of materials and processes used were the duration of storage in the freezer of 36 to 48 h; vertically cutting strawberry before OD; osmotic dehydration agents with a concentration of 50°Brix; immersion time for 30 min at temperature a 30°C; and freeze-drying time of 24 h. Results of each treatment in terms of physical quality parameters (color of skin fruit (L*a*b*), change of color (ΔE), and hardness) and phytochemical quality parameters (water content, vitamin C, total phenolic content, and antioxidant activity by DPPH) were compared and discussed. The osmotic dehydration process causes a water loss of 13%, has a significant difference on the parameters of colors (redness and color of change), hardness, vitamin C, total phenolic content, and antioxidant activity by DPPH.

Experimental Study and Modelling of the Sublimation and Desorption Periods for Freeze Drying of Apple, Banana and Strawberry

Slices of fresh apple, banana and strawberry were frozen at -20 oC and freeze-dried using a shelf temperature of 40 oC. Theoretical expressions were proposed to predict vapor transfer kinetics during the primary and secondary drying stages. In the former, a model that predicts the sublimation rate as a function of time, considering the increasing dried layer thickness, was used, which improves greatly the sublimation time equation offered in several textbooks without adding much complexity. In the latter, an analytical solution of the unsteady state diffusion equation was applied. Permeabilities were determined for the primary drying model at an absolute pressure of about 30 Pa, though the relevant kinetic coefficient combines permeability and the mass of ice to sublime relative to the dry matter (sublimation kinetic coefficient). In the secondary drying stage, diffusion coefficients of vapor in the dried layer were in the order of 10−09 m2s−1 for pressures of about 3-5 Pa. In both periods, agreement of predicted and experimental values was more than satisfactory. A minimum freeze-drying time of 12, 6.8 and 8.7 h, considering a final moisture content of 4% w/w, was calculated for apple, banana and strawberry, respectively. Normalized drying curves showed a faster sublimation rate for banana, intermediate for strawberry and slowest for apple. On the other hand, desorption curves showed a faster desorption rate for apple, intermediate for banana and slower for strawberry. In each period, the ordering of the relevant kinetic coefficients (sublimation and diffusion coefficients, respectively) represented the ordering of experimental curves.

Study on Designing and Manufacturing the Freeze Drying System with the Process of Freezing Moist Materials inside the Freeze Drying Chamber to Preserve Valuable Products

Freeze drying is one of the most advanced drying technologies for food processing and preserving using temperature under 0oC or under the freezing point, and pressure of drying chamber environment under 4.58mmHg to process foods. This method helps to maintain the initial quality of proteins, lipids, carbohydrates, vitamins, bioactive substances and sensory activities… In this study, the calculation and design were carried out to find suitable technology parameters to make the freeze drying system in which the freezing process occurred inside the freeze drying chamber. Heat was transferred by short wavelength thermal radiation, l = 50´10-3 m. As a result, time of freeze drying had been shortened to 13.33h/batch. The system was successfully manufactured, showed the steadily working, producing the high quality products, and reduced products price. In the conditions of Vietnam, the freeze drying system replacing that of other countries is the indispensable factor to apply for processing and preserving foods.

Development of Nanocrystal Compressed Minitablets for Chronotherapeutic Drug Delivery.

The present work aimed to develop a chronotherapeutic system of valsartan (VS) using nanocrystal formulation to improve dissolution. VS nanocrystals (VS-NC) were fabricated using modified anti-solvent precipitation by employing a Box–Behnken design to optimize various process variables. Based on the desirability approach, a formulation containing 2.5% poloxamer, a freezing temperature of −25 °C, and 24 h of freeze-drying time can fulfill the optimized formulation’s requirements to result in a particle size of 219.68 nm, 0.201 polydispersity index, and zeta potential of −38.26 mV. Optimized VS-NC formulation was compressed (VNM) and coated subsequently with ethyl cellulose and HPMC E 5. At the same time, fast dissolving tablets of VS were designed, and the best formulation was loaded with VNM into a capsule size 1 (average fill weight—400–500 mg, lock length—19.30 mm, external diameter: Cap—6.91 mm; Body—6.63 mm). The final tab in cap (tablet-in-capsule) system was studied for in vitro dissolution profile to confirm the chronotherapeutic release of VS. As required, a bi-pulse release of VS was identified with a lag time of 5 h. The accelerated stability studies confirmed no significant changes in the dissolution profiles of the tab in cap system (f2 similarity profile: >90). To conclude, the tab in cap system was successfully developed to induce a dual pulsatile release, which will ensure bedtime dosing with release after a lag-time to match with early morning circadian spikes.

Stability of spouted bed during spray cold coating on the surface of carrier particles

Abstract The rapid freezing of droplets on the surface of cold carrier particles can reduce the spray freeze-drying time. The coating freezing process can be treated in batch by using a spouted bed and the bed stability is the key. The freezing process of droplets would agglomerate the carrier particles. By analyzing the standard deviation of the bed pressure drop and the fluctuation of the bed pressure, the stable operating conditions of the spouted bed under cold coating were studied, and a dynamic adjustment method of the inlet air velocity to maintain stable spouting was proposed. The results show that the stable operating air velocity range can be described useing the standard deviation of pressure fluctuations. Before bed collapse occurs, it will experience an unstable spouting process, which causes the bed pressure to fluctuate a standard deviation of less than 15 Pa after more than 40 Pa.

Vacuum freeze-drying of tilapia skin affects the properties of skin and extracted gelatins

Herein, the effects of vacuum freeze-drying treatment of tilapia skin on the properties of skin, the molecular properties of extracted gelatins, and the emulsion stabilization properties of extracted gelatins were studied. The results suggested that all the bound, entrapped, and free water molecules were simultaneously sublimated (quickly at the first 30 min and then slowly) by sublimation in the vacuum freeze-drying process. Long vacuum freeze-drying times (60 and 150 min) decreased the amount of the four bands in SDS-PAGE pattern, increased β-sheet and random coil percentages, and decreased other three secondary structure percentages of extracted gelatins. Finally, vacuum freeze-drying of tilapia skin increased the emulsion stability of fish oil-loaded oil-in-water emulsions. This work provided basic knowledges to illustrate the effect of vacuum freeze-drying of protein-enriched tissues on the molecular and functional properties of extracted proteins. It also provided a potential route to increase the emulsion stabilization ability of proteins.

100% Control of Controlled Ice Nucleation Vials by Camera-Supported Optical Inspection in Freeze-Drying.

Freeze-drying is the drying technology of choice for sensitive biological drugs. On the one side, it is admired for its suitability for the stabilization of sensitive molecules. On the other side, it is a time-consuming production step posing challenges in process development and technology transfer. The application of controlled ice nucleation is one elegant approach to shorten freeze-drying times significantly and at the same time increase batch homogeneity. However, a reliable 100% control of the controlled nucleation step in each vial is essential, considering the impact of the nucleation temperature on product quality attributes. In this study, we introduce a camera-supported optical inspection method that utilizes the different superficial cake structures seen in controlled and random nucleated lyophilizates. Derived from the grayscale analysis, the new distinguishing criterion "average edge brightness" is introduced. Four different formulations containing Sucrose, Trehalose, and/or bovine serum albumin were freeze dried with random or controlled nucleation and analyzed with the new technology. A proof of concept is provided by the analysis of a similar-to-market lyophilized monoclonal antibody formulation freeze-dried with three different freezing protocols covering different nucleation profiles. For all investigated formulations and process conditions, the clear discrimination of controlled and randomly nucleated vials was possible. By this, the technology allowed for reliable, noninvasive, and automatable 100% monitoring of controlled nucleation success after freeze-drying.

Energy and Quality Aspects of Freeze-Drying Preceded by Traditional and Novel Pre-Treatment Methods as Exemplified by Red Bell Pepper

Freeze-drying is one of the most expensive and most energy intensive processes applied in food technology. Therefore, there have been significant efforts to reduce the freeze-drying time and decrease its energy consumption. The aim of this work was to analyze the effect of pulsed electric field (PEF), ultrasound (US), and hybrid treatment (PEF-US) and compare them with the effect of blanching (BL) on the freeze-drying kinetics, energy consumption, greenhouse gasses emission, and physical quality of the product. The freeze-drying process was applied to red bell peppers after pretreatment operations. Results showed that application of BL, PEF, US, or PEF-US reduces freeze-drying time and decreases energy consumption. Among the tested methods, the combination of PEF performed at 1 kJ/kg and US was the most effective in reduction of greenhouse gas emission. BL samples exhibited the highest porosity, but from a statistical point of view, most of the PEF-US treated materials did not differ from it. The smallest color changes were noted for US pre-treated bell peppers (ΔE = 9.4), whereas BL, PEF, and PEF-US material was characterized by ΔE of 15.2–28.5. Performed research indicates the application of pre-treatment may improve the sustainability of freeze-drying process and quality of freeze-dried bell pepper.

Evaluation of Microwave Vacuum Drying as an Alternative to Freeze-Drying of Biologics and Vaccines: the Power of Simple Modeling to Identify a Mechanism for Faster Drying Times Achieved with Microwave

Vial-based lyophilization for biopharmaceuticals has been an indispensable cornerstone process for over 50 years. However, the process is not without significant challenges. Capital costs to realize a lyophilized drug product facility, for example, are very high. Similarly, heat and mass transfer limitations inherent in lyophilization result in drying cycle on the order of several days while putting practical constraints on available formulation space, such as solute mass percentage or fill volume in a vial. Through collaboration with an external partner, we are exploring microwave vacuum drying (MVD) as a faster drying process to vial lyophilization wherein the heat transfer process occurs by microwave radiation instead of pure conduction from the vial. Drying using this radiative process demonstrates greater than 80% reduction in drying time over traditional freeze-drying times while maintaining product activity and stability. Such reduction in freeze-drying process times from days to several hours is a welcome change as it enables flexible manufacturing by being able to better react to changes either in terms of product volume for on-demand manufacturing scenarios or facilities for production (e.g., scale-out over scale-up). Additionally, by utilizing first-principle modeling coupled with experimental verification, a mechanism for faster drying times associated with MVD is proposed in this article. This research, to the best of our knowledge, forms the very first report of utilizing microwave vacuum drying for vaccines while utilizing the power of simplified models to understand drying principles associated with MVD.

Fortified and freeze-dried kiwi fruit (Actinidia deliciosa): quality and sensory assessment

Abstract Kiwi fruit (Actinidia deliciosa) (KF) is one of the best fruits available due to its large amount of nutrients. Despite its many health benefits, there are no previous reports on its preparation in other readily ingestible forms. The objective of the present study was to make a new food product from KF. The KF pulp was fortified and blended with several raw materials (such as rice flour and oat flour) using a stepwise short time addition and mixing methodology since this avoids unwanted biochemical and chemical reactions. The blended and reduced moisture KF paste was freeze-dried on a round silver coated steel plate (RSCSP), supplying the heat of sublimation using a newly designed cubic heater. The freeze-drying (FD) time was 4.5 h and the drying kinetics were studied using four established models. The effective moisture diffusivity (Deff) during FD (at 50 °C) was 1.532 x 10-6 m2/s and the activation energy (E) estimated for the FD was 28.35 kJ/mol. The freeze-dried sample was ground and placed under vacuum to reduce the weathering effects. The quality of the stored product was evaluated using the proximate analysis, physicochemical analysis and a sensory evaluation using a hedonic scale. The raw, fresh KF had a moisture content of 85.07% and the final freeze-dried product one of 3%. The carbohydrate, total sugar, protein, fat, total ash, crude fibre and vitamin C contents of the final product increased by 563%, 400%, 355%, 386%, 672%, 106%, and 117% respectively. Of the 66 panelists, the % consumer acceptances for the different attributes were: sweetness (68.18%), sourness (90.91%), saltiness (100%), bitterness (100%), flavour (95.45%), texture (77.27%) and overall acceptability (81.82%). Using conventional freeze-drying (CFD) for blended KF pulp without fortification, with the same RSCSP and the same cubic heater for sublimation, the drying time was found to be 7 h to reach the same final moisture content of 3%.

Novel Ingredients Based on Grapefruit Freeze-Dried Formulations: Nutritional and Bioactive Value.

Grapefruit is a fruit with interesting nutritional value and functional properties, but a short life. Freeze-drying (FD) is a valuable technique as it produces high-quality dehydrated products. This study is aimed to obtain new food ingredients based on freeze-dried grapefruit formulated with high molecular weight solutes (gum arabic and bamboo fiber) in three different proportions (F1, F2, and F3). To improve the FD, a mild microwave drying pre-treatment was applied. Influence of the water content and the presence of high molecular weight solutes on freeze-drying kinetics was tested by Midilli-Kucuk and Page models. The best FD kinetic model fit on grapefruit powders were Midilli-Kucuk for F2 and F3, and Page for F1, and the adequate freeze-drying times for F1, F2, and F3 were 24, 16, and 18 h, respectively. Final samples were evaluated for nutritional and antioxidant capacity. Gum arabic and bamboo fiber present a protector effect, which results in a significant antioxidant capacity due to the protection of flavonoids and antioxidant vitamins. These novel food ingredients could be of great interest for the food industry in order to develop foods with improved antioxidant capacity as well as enriched in natural fibers and/or micronutrients.

Impact of pulsed electric fields on physical properties of freeze-dried apple tissue

Abstract The aim of this study was to analyze the impact of pulsed electric field (PEF) pre-treatment of apple tissue on kinetics of freeze-drying preceded by vacuum freezing and physical properties of such processed material. PEF intensified freeze-drying kinetics and thus reduced processing time by 57% in comparison to untreated apples slices. Furthermore, the effective water diffusion coefficient increased by 44% as a result of PEF application. Water activity changes during storage of freeze-dried apple tissue were more evident in the case of untreated material albeit initial water activity was higher in the case of electroporated samples. As proved by thermal properties measurements these differences were linked to higher crystallinity of the PEF treated samples (35.5%) in comparison to the untreated material (11.0%). The freeze-dried fruits subjected to PEF pretreatment absorbed more water than the untreated samples while no changes were observed for hygroscopicity and loss of the soluble solids during rehydration. Industrial relevance Obtained results confirm that application of pulsed electric field before freeze-drying makes possible to obtain high quality freeze-dried product preceded by vacuum freezing performed inside freeze-dryer which could reduce freeze-drying time. Since the rehydration capacity of PEF treated material, expressed as ability to absorb water, is better than untreated samples the application of this method could be beneficial when designing instant products. Performed research indicates also that PEF treated freeze-dried apples exhibit better stability expressed by water activity which in turn is related to crystallinity. What more, higher crystallinity of PEF pre-treated freeze-dried samples not only complements the explanation of different physical properties in comparison with intact freeze-dried material but also suggest that sensorial properties may vary.