Vacuum Freeze-drying Research Articles

Structures and compositions of biofilms in moving bed biofilm reactors pretreated by four drying methods

Research has so far paid little attention to the impact of the drying method on the structural and compositional analyses of biofilms from moving bed biofilm reactors (MBBRs). To ensure that the biofilm was derived from a steady operation phase of the MBBR, in this study, stable values of the chemical oxygen demand (COD), PO43-, total nitrogen (TN), ammonia–nitrogen (NH4-N), NO3-N and NO2-N concentration, and the biofilm dry weight were obtained after 22 d of operation. Four drying methods (supercritical CO2 drying, vacuum freeze-drying, heat drying, and natural drying) were used to pretreat the biofilms, and the changes in biofilm structures and compositions were investigated in detail. The supercritical CO2 drying and vacuum freeze-drying both maintained the biofilm compositions, while vacuum freeze-drying increased the average pore diameter of the biofilm more than five times that of the biofilm obtained by supercritical CO2 drying. In addition, heat drying and natural drying both damaged the structures and compositions of the biofilms, and heat drying in particular could cause structural collapse, surface charge declines of at least 20%, C and N elemental losses, and biomacromolecule (proteins, polysaccharides, and lipids) losses. The results from this investigation will aid in elucidating the appropriate drying methods for analyzing biofilm structures and compositions.

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.

Grey Correlation Analysis of Drying Characteristics and Quality of Hypsizygus marmoreus (Crab-Flavoured Mushroom) By-Products.

The physical properties and nutritional quality of H. marmoreus by-products (HMB) dried by different methods were comprehensively evaluated by a rigorous statistical method of grey correlation analysis. The results indicated that different drying methods had significant impacts on the characteristics of HMB. Heat pump drying (HPD) was conducive to the preservation of protein and reducing sugar, and hot air drying (HAD) maintained a high content of total flavonoids. The highest fat, polysaccharide, and total phenolic contents were obtained by heated vacuum freeze-drying (H-VFD) treatment. The unheated vacuum freeze-drying (UH-VFD) treatment achieved bright colour, lacunose texture profile, and looser organization structure. The grey correlation analysis showed that UH-VFD and H-VFD had higher-weighted correlation degrees than HPD and HAD. HMB had many higher nutritional components than commodity specifications, especially protein, fat, polyphenols, and amino acids, and had potential applications in the food industry as functional foods and nutraceutical agents.

Preparation and thermal energy storage properties of shaped composite phase change materials with highly aligned honeycomb BN aerogel by freeze-vacuum drying under the control of a temperature gradient

Preparation and thermal energy storage properties of shaped composite phase change materials with highly aligned honeycomb BN aerogel by freeze-vacuum drying under the control of a temperature gradient

Magnetite nanoparticles decorated on cellulose aerogel for p-nitrophenol Fenton degradation: Effects of the active phase loading, cross-linker agent and preparation method

Magnetite nanoparticles (Fe3O4 NPs) are among the most effective Fenton-Like heterogeneous catalysts for degrading environmental contaminants. However, Fe3O4 NPs aggregate easily and have poor dispersion stability because of their magnetic properties, which seriously decrease their catalytic efficiency. In this study, a novel environmentally friendly method for synthesising Fe3O4@CA was proposed. Fe3O4 NPs were immobilized on the 3D cellulose aerogels (CAs) in order to augment the degradation efficiency of p-nitrophenol (PNP) treatment and make the separation of the catalyst accessible by vacuum filtration method. Besides, CAs were fabricated from a cellulose source extracted from water hyacinth by using different cross-linking agents, such as kymene (KM) and polyvinyl alcohol–glutaraldehyde system (PVA–GA), and other drying methods, including vacuum thermal drying and freeze drying, were evaluated in the synthesis process. As-synthesized samples were analysed by various methods, including Powder X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray analysis and Brunauer–Emmett–Teller. Then, using ultraviolet–visible spectroscopy, the difference in the degradability of PNP of the obtained material samples was also investigated to determine their potential applications. Results highlighted that the Fe3O4-3@CA-KF catalyst with an Fe3O4 loading of 0.40 g/gCA used KM as a cross-linker and the freeze-drying method demonstrated the highest PNP removal efficiency (92.5 %) in all Fe3O4@CA samples with a H2O2 content of 5 g/L. The degradation kinetics and well-fitted pseudo-first-order model were investigated. Notably, after five successive PNP degradation experiments, this catalyst retained ∼80 % of the ability to degrade PNP, indicating its outstanding reusability. In environmental remediation, this study provides valuable insights into the development of simply separated and high-efficiency catalysts for heterogeneous catalytic reactions.

Impact of the Drying Procedure and Botanical Origin on the Physico-Chemical and Potentially Bioactive Properties of Honey Powders

This study was aimed at researching the impact of the drying procedure (using the most appropriate honey–maltodextrin concentration for each drying technique) and botanical origin of honey on the physicochemical and potentially bioactive properties of honey powders that were made using maltodextrin as a carrier. The research was carried out with thyme, lavender, vetch and multifloral honey dehydrated using vacuum drying and freeze drying. The analysed parameters were moisture, water activity, colour, glass transition temperature, powder recovery, hygroscopic index and rate, tapped density, solubility, and phenolics as well as antiradical (ABTS•+, ROO•, •OH and O2•−), anti-inflammatory and antimicrobial (against Staphylococcus aureus, Escherichia coli and Listeria monocytogenes) activities. Freeze drying provided the highest recoveries. Powders obtained using freeze drying showed higher moisture and solubility as well as lower glass transition temperature, density and hygroscopicity than those obtained using vacuum drying. Hygroscopicity, glass transition temperature and antimicrobial activity against St. aureus depended on the drying procedure–honey concentration. Colour, anti-O2•− activity and antimicrobial activity against L. monocytogenes depended on the botanical origin of the raw honey. Moisture, solubility, density, total phenolic content, anti-ABTS•+ and anti-ROO• activities as well as anti-inflammatory activity and antimicrobial activity against E. coli depended on the drying procedure–honey concentration and botanical origin.

Freeze-thaw pretreatment improves the vacuum freeze-drying efficiency and storage stability of goji berry (Lycium barbarum. L.)

In order to improve the efficiency of vacuum freeze-drying of goji berry, the effects of multiple freeze-thaw pretreatments (FT) on the water distribution, microstructure, drying characteristics and physicochemical properties of the goji berry were studied. FT effectively shortened the vacuum freeze-drying duration by 4–6 h and reduced the energy consumption by 10.0–15.1 g/100 g compared with the traditional alkaline-dewaxing method. Further analysis revealed that FT accelerated the whole drying process, especially the rapid drying stage, due to the decrease in the bound water. In addition, FT effectively preserved the physicochemical properties, including shrinkage and hardness of goji berries after freeze-drying treatment. In particular, the deterioration of carotenoid-based red color was alleviated after 6 months of storage of freeze-dried goji berry, during which the degradation of carotenoids was significantly inhibited. Comprehensive analysis established that two freeze-thaw cycles are more suitable for the production of dried berries in practice.

Effects of different drying methods on quality and water distribution of Lycium barbarum

AbstractAlthough Lycium barbarum is a valuable medicinal food, it is unfortunately not easy to store due to its high moisture content. In order to maximize the preservation of the medicinal value of L. barbarum, drying is increasingly used for its storage. Motivated by the need to better understand and improve the drying of L. barbarum, in this study, the VFD (vacuum freeze drying) and HD (hot air drying) are employed as drying processes, and the rehydration ratio, drying time, specific energy consumption, sensory characteristics, moisture ratio, energy consumption, moisture mobility, and amino acids and flavonoids content of dried L. barbarum are comprehensively analyzed. The results show that, after VFD, L. barbarum has lower hardness (71.53 ± 1.68), higher rehydration ratio (1.31 ± 0.02), larger volume, plump, round and smooth surface, and similar color to the fresh L. barbarum. At the same time, compared with the sample after HD, the moisture ratio of L. barbarum after VFD is lower (1.4 ± 0.1), and its content of free water is almost negligible (2.2%). In addition, the amino acids and flavonoids content of L. barbarum after VFD are closer to those of the fresh product (133.7 μmol/g, 5.69 mg/g). Based on the analysis of the drying effect on the physical and chemical properties of L. barbarum, we conclude that VFD is a promising processing technology. However, HD proves to greatly reduce the specific energy consumption and drying time when raising the temperature appropriately, whereas VFD could not achieve the same result by increasing the heating rate of VFD.Practical applicationsIn this paper, based on the mechanism of different drying methods, the quality of L. barbarum products after drying was compared, and the water distribution in the drying process was analyzed. It is found that using VFD technology to dry L. barbarum can improve the production efficiency of L. barbarum industry and the quality of L. barbarum products. Meanwhile, the research results can provide reference for the optimization of VFD system and the scientific formulation of process parameters.

Vacuum freeze dryer technology for extending the shelf life of food and protecting the environment: a scenario study of the energy efficiency.

This study focused into vacuum freeze dryer technology for increasing food shelf life in a drying food technology. The determinants of energy consumption increase as the energy density of food production and storage increases. Reducing the amount of energy used for drying, freezing, chilling, refrigeration, and air conditioning is becoming more important. The objective of this study was to extend food's shelf life utilizing creative and novel technical approaches, such as vacuum freeze-drying's energy-efficient process. Despite being a part of this investigation, the vacuum freeze drier was created using environmentally benign energy sources. To minimize the carbon footprint of food preservation, it is essential to use eco-friendly energy sources in chilling storage. According to the first law of thermodynamics, the energy efficiency at 1 atm pressure and 25 [°C] temperature (neglecting potential and kinetic energies) in the dead state is calculated under thermal equilibrium conditions. In this study, the energy efficiency was shown according to 5 different scenarios. The results of energy efficiencies are as follows: η1 is from 14.3 to 21.4%, η2 is from 20.7 to 31.0%, η3 is from 27.3 to 40.9%, η4 is from 32.1 to 48.1%, and η5 is from 34.6 to 51.9%, respectively. This analysis demonstrates that the energy efficiency improved from 12 to 18 h. In this study, optimizations with scenarios were employed considering vacuum freeze-drying technology in the plant with sustainable energy sources can considerably improve food shelf life while limiting our environmental impact.

Effects of chia seed gum on the physicochemical properties of frozen dough and the quality of dumplings

This study was designed to investigate the properties of chia seed gum (CSG) and its use in frozen dough. The CSG prepared by vacuum freeze-drying had the lowest water separation (4.22 ± 0.11 %) after three freeze–thaw cycles and the best color among the samples. The addition of 0.4 % to 1.0 % CSG significantly increased the peak, trough and final viscosity and decreased the breakdown and setback of the flour. The water absorption and cooking stability of the dough increased with increasing CSG content. The addition of 0.8 %–1.0 % CSG significantly increased the content of strongly bound water in dough during frozen storage. The CSG improved the texture of dough, and there were no significant differences in hardness, springiness, cohesiveness or chewiness of dough with 0.8 %–1.0 % CSG during frozen storage for 30 days. The cooking loss rate and the cracking rate of the dumpling wrappers with 0.8 % CSG were reduced by 2.31 % and 21.34 %, respectively. In conclusion, CSG can be used to improve the quality of wheat dough and its products and has promising applications in flour products.

Comparison of different drying techniques for Zanthoxylum bungeanum leaves: Changes in color, microstructure, antioxidant capacities, and volatile components

Herein, the effects of different drying methods, namely, indoor natural drying (ND), vacuum freeze drying (FD), vacuum drying (VD), hot air drying (AD), and heat-pump drying (PD) on the qualities of Zanthoxylum bungeanum leaves were investigated. The VD-treated Z. bungeanum leaves retained their original color to a greater extent. The microstructure was significantly affected by the temperature, as evidenced by scanning electron microscopy. In addition, FD, and AD both led to high and relatively similar contents of the various components, including the total phenols, flavonoids, proteins, and sugars. The strongest antioxidant capacities resulted from AD treatment, with total phenolic and flavonoid contents as high as 65.07 mg GAE/g dw and 133.2 mg RE/g dw, respectively. Moreover, 107 volatile organic compounds (VOCs) were identified using headspace solid-phase microextraction–mass spectrometry coupled with gas chromatography–mass spectrometry and classified into eight types according to their structures. The different drying methods were found to produce variations in the number and relative contents of the VOCs, which were mainly olefins and alcohols. A comprehensive evaluation of the economic value and product quality concluded that AD is the most suitable drying method for Z. bungeanum leaves, owing to its high efficiency, low cost, and good product quality.

The impact of different drying methods on the physical properties, bioactive components, antioxidant capacity, volatile components and industrial application of coffee peel.

This study evaluated the effects of hot air drying (HAD), microwave drying (MD), vacuum drying (VD), sun drying (SD) and vacuum freeze drying (VFD) on the physical properties, bioactive components, antioxidant capacity, volatile components and industrial application of coffee peel. The results showed VFD could retain the appearance color, total phenolics (19.49 mg GAE/g DW), total flavonoids (9.65 mg CE/g DW), caffeine (3.15 mg/g DW), trigonelline (2.71 mg/g DW), and antioxidant capacities of fresh sample to the greatest extent, but its operating cost was significantly higher than other treatments and total volatile components were in the minimum levels. HAD and SD exhibited the highest loss rates of total phenols and antioxidant capacities, exceeding 50%. MD offered the lowest operating cost, superior retention of bioactive components, and the richest variety and quantity of volatile compounds. Therefore, it is recommended to use MD to dehydrate the coffee peel in actual production.

Screening of Lactiplantibacillus plantarum 67 with Strong Adhesion to Caco-2 Cells and the Effects of Protective Agents on Its Adhesion Ability during Vacuum Freeze Drying.

Adhesion to the intestinal tract provides the foundation for Lactobacillus to exert its benefits. Vacuum freeze-drying (VFD) is currently one of the main processing methods for Lactobacillus products. Therefore, the effects of VFD on the adhesion and survival of Lactiplantibacillus plantarum 67 were investigated in this study. The results show that L. plantarum 67 exhibits remarkable tolerance following successive exposure to simulated saliva, gastric juice and intestinal juice, and also has a strong adhesion ability to Caco-2 cells. The adhesion and survival rates of L. plantarum 67 significantly decreased after VFD in phosphate-buffered saline (PBS), whereas they significantly increased in protective agents (PAs) (p < 0.05). Scanning electron microscope observations show that L. plantarum 67 aggregated more to Caco-2 cells in PAs than in PBS, and its shape and size were protected. Proteomics detection findings indicated that differentially expressed proteins (DEPs) related to adhesins and vitality and their pathways in L. plantarum 67 were significantly affected by VFD (p < 0.05). However, the expression of DEPs (such as cold shock protein, cell surface protein, adherence protein, chitin-binding domain and extracellular transglycosylase, membrane-bound protein) was improved by PAs. Compared with PBS, the PAs significantly adjusted the phosphotransferase system and amino sugar and nucleotide sugar metabolism pathways (p < 0.05). VFD decreased the adhesion and vitality of L. plantarum 67, while the PAs could exert protective effects by regulating proteins and pathways related to adhesion and vitality.

Heat Flux Analysis and Assessment of Drying Kinetics during Lyophilization of Fruits in a Pilot-Scale Freeze Dryer.

Vacuum freeze-drying as a process for achieving high product quality has attracted increasing attention in the last decade. Particularly in the pharmaceutical field and food processing industries, lyophilization can produce high-quality products compared to samples dried by conventional methods. Despite its benefits, lyophilization is a time-consuming and costly process that requires optimization of a number of process parameters, including shelf temperature, chamber pressure, freezing rate, and process time. This paper reports on the implementation of heat flux measurements that allow noninvasive real-time determination of the endpoint of the primary drying stage as an essential parameter for the effective optimization of the overall drying time. Quantitative analysis of the drying kinetics of five fruits (kiwifruit, avocado, Asian pear, persimmon, and passion fruit) was assessed by comparing the heat flux and temperature profiles of samples during the lyophilization process. For a 24 h lyophilization cycle, average heat fluxes in the primary drying phase ranged from 250 to 570 W/m2. A significant correlation was found between the temperature and heat flux distributions at the estimated endpoint of the sublimation process and the corresponding transition into the secondary drying stage. Furthermore, good agreement was also found for the freezing phase. The use of real-time heat flux measurements proved to be a cost-effective experimental method to better understand the process variables in order to reduce the lyophilization cycle time and overall energy consumption.

Low-Temperature Vacuum Drying on Broccoli: Enhanced Anti-Inflammatory and Anti-Proliferative Properties Regarding Other Drying Methods.

Low-temperature vacuum drying (LTVD) has shown great potential for drying vegetables. It could avoid excessive degradations of active compounds with potential therapeutic agents. In this study, the effect on several relevant bioactive compounds, anti-inflammatory activity, and anti-proliferative activity of broccoli (Brassica oleracea var. italica) were evaluated. Effects of other drying methods, including vacuum drying (VD), convective drying (CD), infrared drying (IRD), and freeze drying (FD), were also comparatively evaluated. The results of all dried samples showed high polyunsaturated fatty acid contents (of up to 71.3%) and essential amino acid contents (of up to 8.63%). The LTVD method stands out above the other drying methods, since it obtained the highest content of total phenols, chlorogenic acid, and ferulic acid. Both the LTVD and CD samples demonstrated high anti-inflammatory and anti-proliferative activities. These CD and LTVD samples were also the most active against the breast carcinoma MDA-MB-23 cell line. Due to the good retention of bioactive compounds via LTVD, the obtained dried broccoli here can be used in a near time as an ingredient for the development of novel natural products with anti-inflammatory and anti-proliferative effects.

Effects of different drying methods on the physical characteristics and non-volatile taste components of Schizophyllum commune

Fresh Schizophyllum commune deteriorates easily after harvest due to its high moisture content and tender texture. Different drying methods can affect food quality differently. The study aimed to investigate the effects of hot air drying at 60 °C and 80 °C (60 °C HAD and 80 °C HAD), ultrasound-assisted hot air drying at 60 °C and 80 °C (US-60 °C HAD and US-80 ℃ HAD), microwave drying (MD), microwave vacuum drying (MVD) and vacuum freeze-drying (VFD) on the physical properties and taste components of Schizophyllum commune. Results showed that VFD group had the best porous honeycomb ultrastructure, and closest color to fresh mushroom. The VFD group had the highest total organic acid content (19.78 mg/g), with particularly high levels of succinic anhydride (6.03 mg/g) and succinic acid (4.99 mg/g). Additionally, VFD showed superior retention rates for 5′-nucleotides (6.45 mg/g) and free amino acids (25.42 mg/g). US-60 ℃ HAD (7.77 mg/g), US-80 ℃ HAD (7.63 mg/g), and VFD (7.40 mg/g) were better at retaining monosodium glutamate-like amino acid. VFD and US-60 ℃ HAD could produce higher equivalent umami concentration values. VFD is a good choice for drying Schizophyllum commune. The research results can provide reference for commercial drying of Schizophyllum commune.

Enhancement of Haskap Vacuum Freeze-Drying Efficiency and Quality Attributes Using Cold Plasma Pretreatment

Enhancement of Haskap Vacuum Freeze-Drying Efficiency and Quality Attributes Using Cold Plasma Pretreatment

Effects of four drying methods on the quality, antioxidant activity and anthocyanin components of blueberry pomace

The effects of drying on the quality, antioxidant activity and anthocyanin components of blueberry pomace were investigated using hot air drying (HAD), freeze-drying (FD), microwave vacuum drying (MVD) and microwave freeze vacuum drying (MFD). The quality, antioxidant activity, and individual anthocyanin compositions of blueberry pomace were evaluated and compared with the non-dried control. MVD produced the highest levels of total phenols, total anthocyanins, total sugars and color values in blueberry pomace while HAD gave the lowest. The ABTS +and DPPH radical scavenging abilities of blueberry pomace were significantly high when MVD was used. Moreover, FD, MVD, and MFD resulted in the retention of significantly more anthocyanin species than HAD as determined by HPLC coupled to the mass spectrometer. Overall, MVD proved to be the best technique for preservation of antioxidant capacity and natural color. Therefore, MVD of blueberry pomace can improve efficiency and productivity of the blueberry fruit processing industry while reducing the environmental burden.Graphical

Effects of different drying methods on physico-chemical properties, bioactive and taste substances of Cynomorium songaricum

Cynomorium songaricum is a typical edible and medicinal plant, also called Suoyang (Chinese name). The effect of different drying methods on Suoyang quality has not yet been performed. Here, four drying methods were tested, including sun drying (SD), microwave drying (MD), hot air drying (HAD), and vacuum freeze drying (VFD), to evaluate the influences of various drying methods on the physico-chemical properties, bioactive and taste substances of dried Suoyang. Results showed that VFD treated samples maintained the original cellular structure and color, and had higher textural properties, antioxidant activities, and rich flavor. In addition, a total of 980 metabolites in four kinds of dried Suoyang were detected and clustered into 9 co-response modules based on utilizing widely targeting metabolomics method and weighted metabolite co-response network analysis (WMCNA). Among the important modules, 3 key metabolites were identified as potential quality markers of overall antioxidant capacity and 30 key metabolites were identified as the main taste substances, which also might be relate to the nutritional value of dried Suoyang. This finding will provide reference for choosing proper drying method that can maintain the quality of dried Suoyang and adapt to industrial production.

Enzyme-sensitive soybean protein isolate/cinnamaldehyde antibacterial microcapsules triggered by blueberry proteases

In this study, enzyme-sensitive microcapsules using soybean protein isolate as the wall material, and cinnamaldehyde as an antimicrobial core material, were prepared by vacuum freeze-drying. The results showed that a 4% solution of soybean protein isolate with cinnamaldehyde added at a 4:1 (w/w) ratio provided an effective microcapsule formulation, with an embedding rate of 62.63 ± 0.95% and a particle size of 347.00 ± 31.18 nm. After lyze-drying, SPI-CA microcapsules showed uneven morphology, sag and agglomeration, but the microcapsules had small particle size and good dispersion stability. The 4%SPI/CA-4:1 microcapsules provided protection for cinnamaldehyde for 12 days. The release of cinnamaldehyde was slow from the 6th day, and the cumulative release was 79.08 ± 3.0% after 12 days. In addition, infrared spectroscopy, XRD and DSC prove that the hydration of soybean protein isolate, electrostatic repulsion charges, and the creation of cinnamaldehyde essential oil nanodroplets resulted in stable microcapsules. The microcapsules produced were successful in providing the controlled release of its antibacterial substance when exposed to natural protease concentrations triggered by fungal growth on blueberries. The release of cinnamaldehyde from SPia-Ca microcapsules was triggered by protease, which was secreted from blueberry by microbial contamination. The developed microcapsule has wide applications, and the results of this study provide new ideas for future food preservation technology development.