Synthesis of Porous Materials and Their Microstructural Control through Ice Templating

Ice-templating is a simple, practical kind of template synthesis which consists of sol-gel polycondensation, unidirectional freezing of hydrosols or hydrogels, and pore-preserving drying method, such as freeze drying, thereby resulting in desirable porous materials. The unidirectional freezing may be achieved by either immersion freezing or contact freezing. Freeze-dried materials contain porous microstructures that are replicas of the ice crystals formed during the unidirectional freezing process. Two similar but slightly different applications of ice-templating will be investigated here. Fabrication of macroporous foam materials by unidirectional freezing of an aqueous suspension of carbon nanotubes (CNTs) dispersed by chitosan is a concrete example of functionalization of an electroconductive foam, which is a composite material made from a polymer and CNTs. As expected, their electroconductive properties can be controlled by the fabrication method and condition. Additional examples of porous materials synthesized by ice-templating are porous microfibers and microhoneycombs of silica, titania, silica-alumina, titania-silica, and even carbon. In the preparation, the morphology and porous structure can be controlled by the freezing conditions and synthesis conditions of the corresponding hydrogels, respectively

The manufacturing of lactobacillus microcapsules by freezing with egg yolk: The analysis of microstructure and the preservation effect against freezing and acid treatments

Encapsulation is an effective strategy to prevent probiotics from environmental damages. The survivability of Lactobacillus is generally reduced under frozen or acid environments. In this study, an attempt was made to encapsulate Lactobacillus into the egg yolk aggregates formed upon freezing. Lactobacillus broth was mixed with liquid egg yolk and frozen at selected temperatures and time periods. After thawing, the number of surviving bacteria was determined. The results showed that freezing with the addition of egg yolk improved Lactobacillus survivability. It was confirmed that freezing increased the number of egg yolk aggregates, and those aggregates coated Lactobacillus after freezing. The encapsulated Lactobacillus was treated at pH 2.5 for 10 min, and the results showed that the encapsulation process increased the acid resistance of Lactobacillus. These results indicate that freezing-induced encapsulation with egg yolk could effectively protect Lactobacillus against freezing and acid treatment. This finding could be useful for the design and preservation of probiotics-based food products

Influence of processing conditions of atmospheric freeze-drying/low-temperature drying on the drying kinetics of sliced fruits and their vitamin C retention

Sliced fruits (apple and kiwi) were dried under atmospheric freeze-drying (AFD) and/or low-temperature drying (LTD) conditions, and the drying kinetics, resultant degree of shrinkage, and vitamin C retention were evaluated. The air temperature programs were set in the range of −20 to 10 °C, and the impact of the sub-zero temperature setting was investigated. As expected, shortening the sub-zero temperature time and increasing the air temperature led to a shorter total drying time. Notably, the application of freezing had an effect to reduce the drying time. The application of the LTD condition without freezing significantly increased the total drying time compared with that of the drying condition with freezing. When the temperature was increased stepwise from −20 to 10 °C, the total drying time was effectively reduced when the sub-zero temperature was maintained for a relatively long time. This was the most practical drying program for maintaining product quality. It was found that drying at sub-zero temperatures has advantages in reducing product shrinkage; however, the impact was not remarkable. The application of sub-zero temperature conditions was advantageous for vitamin C retention for both apple and kiwi drying. However, if the negative effect of freezing on quality is significant, simple LTD conditions may be a good compromise for balancing total drying time and product quality

Исследование влияния термической обработки на вид излома ударных образцов и трещиностойкость сталей типа 06Г2МБТ

В работе исследованы образцы Шарпи низкоуглеродистых трубных сталей типа 06Г2МБТ после контролируемой прокатки и ускоренного охлаждения и термической обработки по различным режимам. На основе литературных данных и результатов собственных экспериментов проведен анализ поверхностей разрушения, изучено влияние температуры нагрева на уровень ударной вязкости стали и вид поверхности излома

Modeling of atmospheric freeze-drying for sliced fruit

[EN] A mathematical model that simulates atmospheric freeze-drying for apple slices was developed based on the classical mass and heat balance equations. When operated above the glass transition temperature, product shrinkage and micro-collapse due to the glass-rubber transition occurred. So, instead of assuming formation of dried and frozen zones, a glassy matrix with particular vapor pressure was assumed. Apparent vapor pressure of apple slices in the glassy state was experimentally measured and summarized in a diagram, and the values in this diagram were employed for the simulation. This approach well predicted drying kinetics with reasonable accuracy with simplified equations.Horie, A.; Kobayashi, T.; Nakagawa, K. (2018). Modeling of atmospheric freeze-drying for sliced fruit. En IDS 2018. 21st International Drying Symposium Proceedings. Editorial Universitat Politècnica de València. 179-186. https://doi.org/10.4995/IDS2018.2018.7643OCS17918

Observation of microstructure change during freeze-drying by in-situ X-ray Computed Tomography

[EN] X-ray computed tomography technique was used to observe microstructure formation during freeze-drying. A specially designed vacuum freeze-drying stage was equipped at the X-ray CT stage, and the frozen and dried microstructures of dextrin solutions were successfully observed. It was confirmed that the many parts of the pore microstructures formed as a replica of the original ice microstructures, whereas some parts formed as a consequence of the dehydration dependent on the relaxation level of the glassy phases, suggesting that the post-freezing annealing is advantageous for avoiding quality loss that relates to the structural deformation of glassy matters.Nakagawa, K.; Tamiya, S.; Sakamoto, S.; Do, G.; Kono, S.; Ochiai, T. (2018). Observation of microstructure change during freeze-drying by in-situ X-ray Computed Tomography. En IDS 2018. 21st International Drying Symposium Proceedings. Editorial Universitat Politècnica de València. 935-942. https://doi.org/10.4995/IDS2018.2018.7642OCS93594

シンキ スイジョウキ フカツ マエショリホウ オ モチイテ コタイ ハイキブツ カラ サクセイシタ メソ サイコウセイ カッセイタン ニ カンスル ケンキュウ

京都大学0048新制・課程博士博士(工学)甲第10231号工博第2294号新制||工||1278(附属図書館)UT51-2003-H652京都大学大学院工学研究科化学工学専攻(主査)教授 田門 肇, 教授 前 一廣, 教授 三浦 孝一学位規則第4条第1項該当Doctor of EngineeringKyoto UniversityDA

Osmotic Dehydration, Drying Kinetics, and Quality Attributes of Osmotic Hot Air-Dried Mango as Affected by Initial Frozen Storage

Using frozen mango for osmotic hot air drying is still uncommon due to a lack of knowledge on the effect of the freezing process on the final product’s quality attributes. This study aimed to investigate the effect of the freezing method (slow and quick freezing) and frozen storage time at −18 °C (0, 1, and 2 months) on mass transfer kinetics during osmotic dehydration, drying kinetics during hot air drying, and final quality attributes of the dried mango. The results indicated that Peleg’s model could describe the water loss and solid gain during the osmotic dehydration in a 38° Brix sugar solution. Freezing before osmotic dehydration reduced the water loss rate while increasing the solid uptake content. Frozen mangoes showed slightly higher drying rates at 50 and 60 °C than the fresh ones. Freezing and frozen storage also retarded the browning reaction and polyphenol oxidase activities. The osmotic-dried mango obtained from frozen mangoes showed a chewy and gummy texture, which could be considered a distinctive texture characteristic for dried mango

Effect of Coagulant Concentration on Soy Protein-Based Fiber for Meat Substitute by Wet Spinning Combined with Ionic Cross-Linking of Alginate

Meat substitutes production using plant-derived materials is attracting attentions as a solution for sustainable protein supply. We have previously reported the fabrication of soy protein-based fibers by combination of wet spinning and ionic cross-linking of alginate. In this study, we focused on the calcium ion concentration in the coagulant solution and alginate concentration in the spinning solution, which are determinant factors for in the gelation of alginate. The fiber diameter was reduced by increasing calcium ion concentration, probably due to the dehydration from fiber induced by osmotic pressure difference with coagulant solution and the suppression of swelling of fiber by the rapid gelation. The hardness of fibers evaluated by texture analysis increased as the concentrations of alginate and calcium ion increased, while the springiness increased with increasing calcium ion concentration but decreased with alginate concentration. The controlling the structure and texture of fibers by the compositions of spinning and coagulant solutions would improve their applicability to meat substitutes