• Journal of Microbiology and Biotechnology
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• v.32 no.12
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• pp.1599-1604
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• 2022

Storage stability of freeze-dried lactic acid bacteria is a critical factor for their cost-effectiveness. Long-term storage of lactic acid bacteria enables microbial industry to reduce distribution costs. Herein, we investigated the effect of cold adaptation under supercooling conditions at -5℃ on the viability of Leuconostoc mesenteroides WiKim32 during the freeze-drying process and subsequent storage. Cold adaptation increased the thickness of exopolysaccharides (EPS) and improved the viability of freeze-dried Leu. mesenteroides WiKim32. Compared to non-adapted cells, cold-adapted cells showed a 35.4% increase in EPS thickness under supercooling conditions. The viability of EPS-hydrolyzed cells was lower than that of untreated cells, implying that EPS plays a role in protection during the freeze-drying process. Cold adaptation increased the storage stability of freeze-dried Leu. mesenteroides WiKim32. Fifty-six days after storage, the highest viability (71.3%) was achieved with cold adaptation at -5℃. When EPS-containing broth was added prior to the freeze-drying process, the viability further increased to 82.7%. These results imply that cold adaptation by supercooling pretreatment would be a good strategy for the long-term storage of Leu. mesenteroides WiKim32.

• Journal of Microbiology and Biotechnology
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• v.12 no.2
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• pp.349-353
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• 2002

Two recombinant bacteria containing luxAB showed an increased tolerance to stresses associated with lyophilization, when the cells were freeze-dried in the presence of trehalose. In the case of a recombinant, UV2, only $2.5\%$ of the original bioluminescence and $2.7\%$ of the cell viability were restored after 4 h of freeze-drying without trehalose, which implies that the cells were heavily damaged during the dehydration. To improve these losses, trehalose was added before freeze-drying using different modes. Trehalose increased the bioluminescence and the viability of freeze-dried UV2 under all conditions tested, and it was also observed that the addition of trehalose to the cultures (final concentration of 0.08 M) for 15 min before the freeze-drying resulted in the restoration of $45\%$ of the original bioluminescence and $50\%$ of the cell viability. Trehalose also showed a similar efficacy with the other luminescent recombinant, YH9. Therefore, it was tentatively concluded that trehalose played a role as a protective agent in the freeze-drying of bacterial cells.

• Biotechnology and Bioprocess Engineering:BBE
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• v.5 no.3
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• pp.202-206
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• 2000

The genetically-engineered Escherichia coli strain, DPD2540, which contains a fabA:::luxCDAbefusion gene, gives a bioluminescent output when membrane fatty acid synthesis is needed. For more pactical application of this strain in the filed as biosensor, freezedrying was adopted. A 12% surcrose solution with Luria-Bertani (LB) broth, as determined by the viability after freeze-drying, was found to be most most effective composition for lyophilization solution among various compositions testitons tested. Rapid freezing with liquid nitrogen also gave the best viability after freeze-drying as compared to samples frozen at-7$0^{\circ}C$ and -2$0^{\circ}C$. The biosensing activities of the cells showed a greater sensitivity when the cells from the expontial phase were freeze-dried. Finally, the optimum temperature for use of the freeze-dried cells in the biodencor field was determined.

• Biomedical Science Letters
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• v.9 no.4
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• pp.195-201
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• 2003

Aromatic hydrocarbons are of major concern among genotoxic chemicals due to their toxicity and persistence. Some microorganisms can utilize aromatic hydrocarbons as carbon and energy sources by inducing expression of catabolic operon(s). The XylR regulatory protein activates transcription of the catabolic enzymes to degrade BTEX (benzene, toluene, ethylbenzene, and xylene) from its cognate promoters, Pu and Ps upon exposure of the cells to the aromatic hydrocarbons. The activity of XylR on the promoters was previously monitored using luciferase luc reporter system. The xylR, its promoter Pr and the promoter Po for the phenolic compound catabolic operon were introduced upstream of firefly luciferase luc in the pGL3b vector to generate about 7.1 kb of pXRBTEX. Here E. coli harboring the plasmid was freeze-dried under various conditions to fin,d optimal conditions for storage and transport. The cell viability and luciferase activity were maintained better, when the cells were freeze-dried at -7$0^{\circ}C$ in the addition of the 10% skim milk or 12% sucrose. However, coaddition of protectants such as 10% skim milk plus 10% glucose or 12% sucrose plus 10% glucose, resulted in much better viability and bioluminescence activity compared with the effect of single addition of each protectant. In addition, it was shown that the freeze-dried cells maintained almost intact bioluminescent activities and cell viability for at least 1 week after freeze-drying. This work demonstrated that the properly freeze-dried recombinant bacterial cells could be utilized as a whole-cell biosensor for simple and rapid monitoring of BTEX in the environment.

• Clinical and Experimental Reproductive Medicine
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• v.51 no.1
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• pp.42-47
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• 2024

Objective: This study evaluated the effects of temperature and storage time on the quality and DNA integrity of freeze-dried sperm from individuals with normozoospermia. Methods: Normal sperm samples from 15 men aged 24 to 40 years were studied. Each sample was divided into six groups: fresh, freezing (frozen in liquid nitrogen), freeze-dried then preserved at room temperature for 1 month (FD-1m-RT), freeze-dried then preserved at room temperature for 2 months (FD-2m-RT), freeze-dried then preserved at 4 ℃ for 1 month (FD-1m-4 ℃), and freeze-dried then preserved at 4 ℃ for 2 months (FD-2m-4 ℃). The morphology, progressive motility, vitality, and DNA integrity of the sperm were evaluated in all groups. Results: In all freeze-dried groups, sperm cells were immotile after rehydration. The freeze-dried groups also showed significantly less sperm vitality than the fresh and frozen groups. Significantly more morphological sperm abnormalities were found in the freeze-dried groups, but freeze-drying did not lead to a significantly higher DNA fragmentation index (DFI). The DFI was significantly higher in the FD-2m-RT group than in the other freeze-dried groups. Conclusion: The freeze-drying method preserved the integrity of sperm DNA. The temperature and duration of storage were also identified as factors that influenced the DFI. Accordingly, more research is needed on ways to improve sperm quality in the freeze-drying process.

• Journal of Microbiology and Biotechnology
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• v.27 no.8
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• pp.1428-1440
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• 2017

Phomopsis sp. XP-8 (an endophytic fungus) was previously found to produce pinoresinol diglucoside (PDG), a major antihypertensive compound of Tu-Chung (the bark of Eucommia ulmoides Oliv.), which is widely used in Chinese traditional medicines. In the present study, two bioconversion systems were developed for the production of PDG in Tris-HCl buffer containing glucose and Phomopsis sp. XP-8 cells (both resting and freeze-dried). When other factors remained unchanged, the bioconversion time, glucose concentration, cell ages, cell dosage, pH, temperature, and stirring speed influenced PDG production in a similar and decreasing manner after an initial increase with increasing levels for each factor. Considering the simultaneous change of various factors, the optimal conditions for PDG production were established as 70 g/l cells (8-day-old), 14 g/l glucose, $28^{\circ}C$, pH 7.5, and 180 rpm for systems employing resting cells, and 3.87 g/l cells, 14.67 g/l glucose, $28^{\circ}C$, pH 7.5, and 180 rpm for systems employing freeze-dried cells. The systems employing freeze-dried cells showed lower peak PDG production ($110.28{\mu}g/l$), but at a much shorter time (12.65 h) compared with resting cells (23.62 mg/l, 91.5 h). The specific PDG production levels were 1.92 and $24{\mu}g$ per gram cells per gram glucose for freeze-dried cells and resting cells, respectively. Both systems indicated a new and potentially efficient way to produce PDG independent of microbial cell growth.

• Korean Journal of Food Science and Technology
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• v.30 no.6
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• pp.1448-1455
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• 1998

Fermented milk was prepared from milk or mixture of milk and apple juice/grape juice, and it was freeze dried. pH change and growth of Lactobacillus acidophilus (KCTC 2182) during freeze drying were studied. The effects of freeze drying on sensory evaluation and volatile aroma compounds in freeze dried sample or reconstituted sample were also studied. Freezing and freeze drying did not affect pH of fermented milk. Number of viable cells of L. acidophilus was markedly reduced during freezing or freeze drying. When number of viable cells in original fermented milk was considered as 100%, survival ratio of viable cells after freezing was $64.5{\sim}85.2%$ and that after freeze drying was $10.0{\sim}21.1%$. When sensory properties of original fermented milk prepared from juice-milk (ratio 15:35) were compared with those of freeze dried/reconstituted sample, sensory properties of original sample were better than those of freeze dried/reconstituted sample. Ethanol, diacetyl, butanol and acetoin were detected in all of original samples and freeze dried/reconstituted samples while acetone was detected in samples containing high amount of grape juice. Volatile aroma compounds in original fermented milk were reduced during freeze drying. L. acidophilus produced ethanol, diacetyl and acetoin during fermentation.

• Korean Journal of Food Science and Technology
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• v.31 no.5
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• pp.1337-1344
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• 1999

Lactic acid bacteria fermented foods were prepared from egg white powder, casein and growth stimulating agent. pH change and growth of Lactbacillus acidophilus(KCTC 2182) during freeze drying were studied. The effects of freeze drying on sensory evaluation. hardness and volatile aroma compounds in freeze dried sample or reconstituted sample were also studied. Freezing and freeze drying did not affect pH of fermented samples. Number of viable cells in original fermented samples was markedly reduced during freezing or freeze drying. When number of viable cells in original fermented sampler was considered at 100%. survival ratio of viable cells after freezing was $72.0{\sim}82.4%$ and that after freeze dying $10.0{\sim}20.4%$. When sensory properties of original fermented samples were compared with those of freeze dried/reconstituted samples, sensory properties of original samples were generally better than those of freeze dried/reconstitute samples. However, the reconstitution property and the acceptability of freeze dried samples were good. Volatile aroma compounds in original fermented samples were reduced during freeze drying. The reduction degree of volatile aroma compounds varied with sample.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.13 no.3
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• pp.265-277
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• 1991

In this study, the healing changes of the implanted bone and its surrounding tissues were examined on the histopathologic basis following implantation of the freeze - dried and radiation - sterilized allogeneic bone in Rectus abdominicus of the rat. This study was performed to see the tissue recations after implantation of the freeze - dried and radiation - sterilized allogeneic bone and whether osteogenesis or osteo - induction or osteo - conduction is happened. And the results were as follows : 1. The shape of the implanted allogeneic bone of the 1, 2 - week group specimen was similar to that of normal bone in light - microscopic finding and the atrophy of cellular organells was found in trans - mission electron - microscopic finding. 2. The implanted allogeneic bone was surrounded with the dense fibroconnective tissues, and infiltration of the chronic inflammatory cells gradually became increased. 3. Hyaline degeneration was observed in the surrounding tissue at the 3, 4, 6 - week group specimen. 4. Light - microscopically the resorption of implanted bone became prominent after 4 - week group and the necrosis of allogeneic bone implant became severe with loss of cell components in lacuna. 5. Electron - microscopically, the osteoclast - like cells ere fond after, 2 - week group. It is summarized that the osteo - conduction potential of the bone is remained just after implanting the freeze - dried and radiation - sterilized allogeneic bone on Rectus abdominicus of the rat, but gradually it disappeared with the gradual increse of chronic inflammatory reaction and osteoclastic activity. So it is suggested that the antigenicity of the freeze - dried and radiation - sterilized bone is remained and it has little osteo - conductive activity when it is implanted in the muscle.

• Korean Journal of Food Science and Technology
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• v.43 no.4
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• pp.509-512
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• 2011

To study the effect of freezing rate on the quality of freeze-dried rice porridge, freeze-dried rice porridge products were prepared with rice porridge pre-frozen at three different temperatures of -20, -40, and -70$^{\circ}C$. The porridge properties such as microstructure, mechanical properties, textural properties, and rehydration rate were determined. Scanning electron microscopy images indicated that fewer air cells were obtained with a larger size of freeze-dried rice porridge frozen at -20$^{\circ}C$ compared with that frozen at -40 and -70$^{\circ}C$. In contrast, quick frozen products at -70$^{\circ}C$ had more dense texture with higher mechanical strength, whereas slow frozen products exhibited higher rehydration rates than those of quick frozen products. In conclusion, the proper choice of pre-freezing temperature plays a decisive role when preparing freeze-dried rice porridge with optimum quality and convenience.