真空冷冻干燥技术在食用菌加工中的应用研究

简析了食用菌冻干制品产业发展形势,概述了真空冷冻干燥技术原理及产品特点,阐述了应用真空冷冻干燥技术加工食用菌制品所需的主要设备、生产工艺流程及操作要点。探讨真空冷冻干燥过程中,各项工艺参数对食用菌干燥特性的影响。介绍食用菌冷冻干燥技术的优越性、技术壁垒及发展前景,旨在为采用真空冷冻干燥技术对食用菌进行干燥加工提供参考。     

Ultrastructural Evidence for the Effects of Freezing in Embryonic Axes of Pisum sativum L. at Various Water Contents

This study investigated the effects of rapid drying (in an airstream) and rapid freezing (in sub-cooled liquid nitrogen) onthe survival and ultrastructural preservation of pea embryonicaxes that had been imbibed for 4 h (desiccation tolerant) and24 h (desiccation sensitive). Maximum survival of all axes inthe absence of freezing was attained. Similarly, 100% survivalwas obtained if freezing was preceded by rapid drying. Axesimbibed for 24 h and not dried were more sensitive to freezingthan undried, 4 h imbibed axes. Ultrastructural examinationshowed no organellar or cytomatrical deformations in axes fromany of the treatments. Some cells of the 24 h imbibed axes showedlocalized plasmalemma abnormalities after railed dehydration.Subsequent to freezing, irregular nuclei were observed and plasmalemmavesiculation occurred. If these axes were not dried prior tofreezing, plasmalemma vesiculation became prominent, clumpingof the cytoskeleton occurred and some wall abnormalities becameapparent. Rapid drying probably increases intercellular soluteconcentrations, and sub-cooled liquid nitrogen will increasethe rate of heat exchange between tissue and cryogen. A combinationof rapid drying and rapid freezing may obviate, or reduce, therequirement for cryoprotectants on freezing of desiccation sensitivetissue.Copyright 1995, 1999 Academic Press Pisum sativum L., pea, embryonic axis, ultrastructure, transmission electron microscopy, cryopreservation, rapid freezing     

香蕉果实冻干过程参数优化的研究

对香蕉果实冻干生产工艺中的物料厚度、冻结方法、加热板温度、干燥室真空度等参数进行比较试验,结果表明,各过程参数对香蕉冻干品质量和产量均有显著的影响。香蕉冻干过程中参数较佳的工艺条件建议为物料厚度选取5~7 mm,采用速冻方法冻结,加热板温度设定45℃,干燥室真空度控制于20~30 Pa。     

Demonstrating Functional Equivalence of Pilot and Production Scale Freeze-Drying of BCG

Process analytical technology (PAT)-tools were used to monitor freeze-drying of Bacille Calmette-Guérin (BCG) at pilot and production scale. Among the evaluated PAT-tools, there is the novel use of the vacuum valve open/close frequency for determining the endpoint of primary drying at production scale. The duration of primary drying, the BCG survival rate, and the residual moisture content (RMC) were evaluated using two different freeze-drying protocols and were found to be independent of the freeze-dryer scale evidencing functional equivalence. The absence of an effect of the freeze-dryer scale on the process underlines the feasibility of the pilot scale freeze-dryer for further BCG freeze-drying process optimization which may be carried out using a medium without BCG.     

Key composition optimization of meat processed protein source by vacuum freeze-drying technology

Vacuum freeze-drying technology is a high technology content, a wide range of knowledge of technology in the field of drying technology is involved, it is also a method of the most complex drying equipment, the largest energy consumption, the highest cost of drying method, but due to the particularity of its dry goods: the freeze-drying food has the advantages of complex water performance is good, cooler and luster of freezing and drying food to maintain good products, less nutrient loss, light weight, easy to carry transportation, easy to long-term preservation, and on the quality is far superior to the obvious advantages of other dried food, making it become the forefront of drying technology research and development. The freeze-drying process of Chinese style ham and western Germany fruit tree tenderloin is studied in this paper, their eutectic point, melting point and collapse temperature, freeze-drying curve and its heat and mass transfer characteristics are got, then the precool temperature and the highest limiting temperature of sublimation interface are determined. The effect of system pressure on freeze-dried rate in freeze-drying process is discussed, and the method of regulating pressure circularly is determined.     

Freeze-drying of solutions of serum albumin containing dimethylsulfoxide.

Although several publications have emphasized the inadvisability of drying biologic materials containing dimethylsulfoxide (DMSO) by sublimation of ice in vacuo, our studies showed a relationship to exist between the relative concentrations of serum albumin, human, and dimethylsulfoxide for successful or unsuccessful freeze-drying of albumin-DMSO solutions. The cycle of freeze-drying for the successful drying of an albumin-DMSO solution was a modification of the cycle used for the successful drying of suspensions of measles virus by sublimation of ice in vacuo. Using nuclear magnetic resonance spectroscopy, a strong, sharp signal for DMSO was obtained in preparations of freeze-dried albumin-DMSO solutions rehydrated with deuterium oxide, D₂O.     

Immunocytochemical study at the ultrastructural level of neurofibrillary degeneration in Alzheimer's disease

Paired Helical Filaments (PHF), as demonstrated at the ultrastructure level, are one of the main pathological landmarks of Alzheimer's disease (AD). A polyclonal rabbit antiserum raised against PHF had been shown to label tangles and the periphery of plaques at the light microscope level. The same antiserum labels PHF specifically at the ultrastructure level, as demonstrated with a postembedding immunogold technique. Normal cytoskeleton constituents and plaque amyloid were not labelled. Specific labelling of a characteristic landmark may be a clue for a biological marker of AD.     

A comparison of conventional SEM techniques, low temperature SEM and the electroscan wet scanning electron microscope to study the structure of a biofilm of Streptococcus crista CR3

Biofilms of Streptococcus crista CR3 were generated on hydroxyapatite (HA) discs for 20 h in a continuous flow system with brain heart infusion broth dripped over the disc at a rate of 6 ml h^-1. This study compares the conventional scanning electron microscope (SEM) preparation techniques, of critical point drying and freeze-drying, with low temperature SEM (LTSEM) and Electroscan generated images of hydrated biofilms, which preserve the integrity of hydrated polymers.
Critical point drying and freeze-drying caused almost complete disappearance of the matrix of extracellular polymeric substances (EPS). Critical point drying, however, showed evenly spaced single or paired cocci remaining on the HA disc whereas freeze-drying caused the biofilm to detach from the HA leaving only patchy clumps of cells visible. By comparison LTSEM preserved the EPS better than critical point drying and freeze-drying, but holes were seen in the top and side of the biofilm and the EPS did show some shrinkage artefacts. An untreated wet biofilm viewed in the Electroscan showed an intact, hydrated, smooth matrix of EPS with cell shapes only visible indistinctly in a canopy of moist EPS. No holes were visible and no shrinkage artefacts were evident. Therefore, Electroscan imaging of the biofilm was the only method that preserved the integrity of the matrix with no apparent shrinkage artefacts.     

Effects of various sugars added to growth and drying media upon thermotolerance and survival throughout storage of freeze-dried Lactobacillus delbrueckii ssp. bulgaricus

The aim of this research effort was to investigate the role of various sugar substrates in the growth medium upon thermotolerance and upon survival during storage after freeze-drying of Lactobacillus bulgaricus. Addition of the sugars tested to the growth medium, and of these and sorbitol to the drying medium (skim milk) was investigated so as to determine whether a relationship exists between growth and drying media, in terms of protection of freeze-dried cells throughout storage. The lowest decrease in viability of L. bulgaricus cells after freeze-drying was obtained when that organism was grown in the presence of mannose. However, L. bulgaricus clearly survived better during storage when cells had been grown in the presence of fructose, lactose or mannose rather than glucose (the standard sugar in the growth medium). A similar effect could not be observed in terms of thermotolerance; in this case, the growth medium supplemented with lactose was found to yield cells bearing the highest heat resistance. Supplementation of the drying medium with glucose, fructose, lactose, mannose or sorbitol led in most cases to enhancement of protection during storage, to a degree that was growth medium-dependent.     

The effect of cooling rate, freeze-drying suspending fluid and culture age on the preservation of Campylobacter pylori

The effects of freezing rate, suspending fluid and age of culture on the ability of four strains of Campylobacter pylori to survive and recover from freeze-drying were examined. Freeze-drying by standard procedures generally resulted in an overall loss in viability of between 3 and 7 log units. The exact cause of poor recovery by C. pylori was not established but strain differences were detected, with NCTC 11637 (type strain) surviving better than NCTC 11638 and NCTC 11639. Recovery of the poorest growing strain (NE 26695) was notably more erratic. The largest loss in viability occurred at the primary drying stage. Losses resulting from freezing and secondary drying were less marked and the rate of freezing had only a marginal effect on recovery. Nineteen different freeze-drying suspending fluids were investigated. Overall the best recovery results were obtained with 5% inositol-broth (or horse serum) plus 25% glucose, at pH 7.0, in which loss of viability was typically about 4 log units. Other factors, such as age of culture and number of viable bacteria in the before-dry suspension, did not have a significant effect on survival. We conclude from these results that C. pylori can survive freeze-drying, albeit in small numbers, but the degree of recovery is apparently largely strain dependent.     

The effect of cooling rate, freeze-drying suspending fluid and culture age on the preservation of Campylobacter pylori

The effects of freezing rate, suspending fluid and age of culture on the ability of four strains of Campylobacter pylori to survive and recover from freeze-drying were examined. Freeze-drying by standard procedures generally resulted in an overall loss in viability of between 3 and 7 log units. The exact cause of poor recovery by C. pylori was not established but strain differences were detected, with NCTC 11637 (type strain) surviving better than NCTC 11638 and NCTC 11639. Recovery of the poorest growing strain (NE 26695) was notably more erratic. The largest loss in viability occurred at the primary drying stage. Losses resulting from freezing and secondary drying were less marked and the rate of freezing had only a marginal effect on recovery. Nineteen different freeze-drying suspending fluids were investigated. Overall the best recovery results were obtained with 5% inositol-broth (or horse serum) plus 25% glucose, at pH 7.0, in which loss of viability was typically about 4 log units. Other factors, such as age of culture and number of viable bacteria in the before-dry suspension, did not have a significant effect on survival. We conclude from these results that C. pylori can survive freeze-drying, albeit in small numbers, but the degree of recovery is apparently largely strain dependent.     

An efficient freeze-drying apparatus

Summary A freeze-drying apparatus with a practical temperature regulating system is described. Degassing, drying and embedding all take place in the drying chamber. The drying temperature can be set at a number of fixed temperature levels which may be chosen anywhere between -70° C and +60° C.     

Microtrabecular lattice of the cytoplasmic ground substance. Artifact or reality

The cytoplasmic ground substance of cultured cells prepared for high voltage transmission electron microscopy (glutaraldehyde/osmium fixed, alcohol or acetone dehydrated, critical-point dried) consists of slender (3-6 nm Diam) strands--the microtrabeculae (55)--that form an irregular three-dimensional lattice (the microtrabecular lattice). The microtrabeculae interconnect the membranous and nonmembranous organelles and are confluent with the cortices of the cytoplast. The lattice is found in all portions of the cytoplast of all cultured cells examined. The possibility that the lattice structure is an artifact of specimen preparation has been tested by (a) subjecting whole cultured cells (WI-38, NRK, chick embryo fibroblasts) to various chemical (aldehydes, osmium tetroxide) and nonchemical (freezing) fixation schedules, (b) examination of model systems (erythrocytes, protein solutions), (c) substantiating the relaibility of critical-point drying, and (d) comparing images of whole cells with conventionally prepared (plastic-embedded) cells. The lattice structure is preserved by chemical and nonchemical fixation, though alterations in ultrastructure can occur especially after prolonged exposure to osmium tetroxide. The critical-point method for drying specimens appears to be reliable as is the freeze-drying method. The discrepancies between images of plastic-embedded and sectioned cells, and images of whole, critical-point dried cells appear to be related, in part, to the electron-scattering properties of the embedding resin. The described observations indicate that the microtrabecular lattice seen in electron micrographs closely represents the nonrandom structure of the cytoplasmic ground substance of living cultured cells.     

Soil drying procedure affects the DNA quantification of <Emphasis Type="Italic">Lactarius vinosus</Emphasis> but does not change the fungal community composition

Drying soil samples before DNA extraction is commonly used for specific fungal DNA quantification and metabarcoding studies, but the impact of different drying procedures on both the specific fungal DNA quantity and the fungal community composition has not been analyzed. We tested three different drying procedures (freeze-drying, oven-drying, and room temperature) on 12 different soil samples to determine (a) the soil mycelium biomass of the ectomycorrhizal species Lactarius vinosus using qPCR with a specifically designed TaqMan® probe and (b) the fungal community composition and diversity using the PacBio® RS II sequencing platform. Mycelium biomass of L. vinosus was significantly greater in the freeze-dried soil samples than in samples dried at oven and room temperature. However, drying procedures had no effect on fungal community composition or on fungal diversity. In addition, there were no significant differences in the proportions of fungi according to their functional roles (moulds vs. mycorrhizal species) in response to drying procedures. Only six out of 1139 operational taxonomic units (OTUs) had increased their relative proportions after soil drying at room temperature, with five of these OTUs classified as mould or yeast species. However, the magnitude of these changes was small, with an overall increase in relative abundance of these OTUs of approximately 2 %. These results suggest that DNA degradation may occur especially after drying soil samples at room temperature, but affecting equally nearly all fungi and therefore causing no significant differences in diversity and community composition. Despite the minimal effects caused by the drying procedures at the fungal community composition, freeze-drying resulted in higher concentrations of L. vinosus DNA and prevented potential colonization from opportunistic species.     

百合离体生殖细胞骨架的扫描电镜观察

从百合的花粉管分离出来的生殖细胞,经表面活化剂Ｔｒｉｔｏｎ Ｘ－１００ 及核糖核酸酶、硫酸铵离析处理。离析后的细胞经临界点干燥,扫描电镜观察显示：在离体生殖细胞的胞质内有一个非常复杂的支架网络系统。这一网络系统有内外两层：外层（靠近细胞膜）网络结构紧密,纤维束粗长;内层（靠近核）网络结构疏松,纤维束短细。一些间接证据显示,这一支架网络系统可能为微管骨架     

Preparation of single molecules and supramolecular complexes for high-resolution metal shadowing

We have compared the appearance and preservation of molecular and supramolecular structures in preparations that were dried in vacuo at room temperature or freeze-dried. Fibrinogen and brain spectrin molecules appear similar in both types of preparation provided that drying at room temperature is performed in the presence of glycerol, which results in an even and reproducible distribution of such molecules (Shotton et al., 1979, J. Mol. Biol. 131, 303-329; Fowler and Erickson, 1979, J. Mol. Biol. 134, 241-249). In the case of crystalline actin sheets, actin filaments, and keratin filaments, freeze-drying preserves structural details that are often completely lost during drying at room temperature, whether or not glycerol is used. On the other hand, keratin filaments prepared by drying in the presence of glycerol display a beaded axial repeat that is probably due to "glycerol decoration." We conclude that although freeze-drying has no clear advantage over glycerol spraying/vacuum-drying in the case of single extended molecules, it may provide insight into the multiple effects of glycerol in specimen preparation. In the case of supramolecular assemblies such as filaments or crystalline sheets, freeze-drying preserves significantly more substructure and surface detail. The loss of such detail during drying at room temperature, probably through collapse phenomena such as distortion and flattening, cannot be prevented by glycerol.     

乳酸菌冻干保藏相关影响因素的研究进展

乳酸菌在冻干保藏过程中受到多种因素的作用,采取适宜的保护措施,在很大程度上可避免或减轻冷冻干燥对细胞带来的损伤.主要介绍了影响乳酸菌冷冻干燥及保藏相关因素的研究进展,这些因素包括:菌种自身的性质、生长因素、亚致死处理、冻干保护介质和复水条件.     

Scanning Electron Microscopic Study of Cytoskeleton in Isolated Generative Cells of Lily

Isolated generative cells of lily were extracted with Triton X-100, ammonium sulphate and RNase. The exposed contents were then viewed in the scanning electron microscope after critical point drying. The treatments revealed that in the cytoplasm of the generative cell there was a reticulate network of cytoskeleton. This reticulate network of cytoskeletal scaffold had two layers: (1) an outer layer (near the membrane) consisting of long and thick fibres that were tightly knitted together, and (2) an inner layer (near the nucleus) consisting of thin and short fibres that were loosely knitted together. Indirect evidence using immunofluorescence techniques for labelling microtubules and TRITC-phalloidin staining of actin microfilaments indicated that the cytoskeleton seen in the scanning electron microscope appeared likely to be a microtubule cytoskeleton rather than a microfilament cytoskeleton.     

Care during freeze-drying of bovine pericardium tissue to be used as a biomaterial: a comparative study

Bovine pericardium (BP) tissue is widely used in the manufacture of bioprosthetics. The effects of freeze-drying on the BP tissue have been studied by some researchers in order to decrease their cytotoxicity due to preservation in formaldehyde solution, and to increase the lifetime of the product in storage. This study was undertaken in order to study the effect of freeze-drying in the structure of BP. To perform this study BP samples were freeze-dried in two different types of freeze-dryers available in our laboratory: a laboratory freeze-dryer, in which it was not possible to control parameters and a pilot freeze-dryer, wherein all parameters during freezing and drying were controlled. After freeze-drying processes, samples were analyzed by SEM, Raman spectroscopy, tensile strength, water uptake tests and TEM. In summary, it has been demonstrated that damages occur in collagen fibers by the loss of bulk water of collagen structure implicating in a drastic decreasing of BP mechanical properties due to its structural alterations. Moreover, it was proven that the collagen fibrils suffered breakage at some points, which can be attributed to the uncontrolled parameters during drying.     

Influence of microencapsulation and spray drying on the viability of Lactobacillus and Bifidobacterium strains

Improved production methods of starter cultures, which constitute the most important element of probiotic preparations, were investigated. The aim of the presented research was to analyse changes in the viability of Lactobacillus. acidophilus and Bifidobacterium bifidum after stabilization (spray drying, liophilization, fluidization drying) and storage in refrigerated conditions for 4 months. The highest numbers of live cells, up to the fourth month of storage in refrigerated conditions, of the order of 10(7) cfu/g preparation were recorded for the B. bifidum DSM 20239 bacteria in which the N-Tack starch for spray drying was applied. Fluidization drying of encapsulated bacteria allowed obtaining a preparation of the comparable number of live bacterial cells up to the fourth month of storage with those encapsulated bacteria, which were subjected to freeze-drying but the former process was much shorter. The highest survivability of the encapsulated L. acidophilus DSM 20079 and B. bifidum DSM 20239 cells subjected to freeze-drying was obtained using skimmed milk as the cryoprotective substance. Stabilization of bacteria by microencapsulation can give a product easy to store and apply to produce dried food composition.