This review provides an overview of development and Computational Fluid Dynamics (CFD) analysis of asymmetric straight-through microchannel (MC) emulsification. Asymmetric straight-through MC arrays, each consisting of a circular MC (inlet side) and a microslot (outlet side), were newly designed for stably producing monodisperse emulsions at droplet productivities higher than previously designed grooved MC arrays and symmetric straight-through MC arrays. Silicon asymmetric straight-through MC array chips were precisely fabricated through repeated processes of deep reactive ion etching. Development of asymmetric straight-through MC emulsification devices and their fundamental characteristics are first described. Monodisperse emulsions were successfully produced via appropriately surface-treated asymmetric straight-through MCs at maximum dispersed-phase fluxes of >1,000 L/(m2 h). Production of monodisperse food-grade emulsions using asymmetric straight-through MC arrays as well as their stability evaluation after layer-by-layer deposition are next introduced. The findings obtained from three-dimensional CFD simulation of droplet generation via asymmetric straight-through MCs are also described. The CFD analysis elucidated that droplet detachment process consisted of three important stages that depend on the internal pressure balance of the dispersed phase in and over the slot.
Changes in electrical and rheological properties of agricultural products were investigated to clarify the softening mechanism of the organization in heating process. Potato, Japanese radish and carrot were used as the sample. These were heated in normal saline solution. Impedance was measured by LCR meter, and dynamic viscoelasticity was measured by the vibrating reed method. As a result, the impedance of potato tuber decreased gradually with an increase in temperature, then decreased rapidly at 65℃. Optical absorbance at 263 nm of the heating saline solution containing the test sample also rose drastically at this temperature, which suggested the release of intracellular nucleic acid related materials. Moreover, dynamic viscoelasticity decreased in the vicinity of this temperature, which suggested that the turgor pressure of the tissue cells was lost because of the cell membrane disruption. Similar phenomena were observed for Japanese radish and carrot although the temperature and the extent of the changes in physical properties were different depending on individuals. These results strongly suggest that the major softening mechanism of agricultural products in heating process exists in the thermal injury of cell membrane which caused the loss in turgor pressure of tissue.
Progressive freeze-concentration of dilute sodium chloride solution was carried out to analyze the effects of the operating conditions of the ice crystal growth rate -(u)- and the stirring rate -(N)- at the ice-liquid interface on the apparent partition coefficient of solute between ice and liquid phase -(K)-. K increased with an increase in the combined operation parameter u/N0.2. Under the similar operating conditions, the ice crystal structure was analyzed with pure water as a sample in progressive freezing. By using polarized light analysis, dendrite ice-crystal structure, which grew in the reversed direction of heat flow, was clearly observed. This ice-crystal structure was not observed under the ordinary light. The mean diameter of the dendrite ice-crystal structure showed a clear negative correlation with the combined operation parameter u/N0.2. These results suggest that the mechanism of the solute incorporation into ice phase in progressive freeze-concentration is its incorporation in the space between the dendrite ice-crystal structure.
Effects of oil fractions and oil-droplet sizes within microcapsules produced by dehydrating oil-in-water (O/W) emulsions on the surface oil content were examined by simulating the two- and three-dimensional models of percolation, depicted by square and cubic models, respectively. The square and cubic models were divided into No×No and No×No×No equal lattices, respectively, where No was the number by which a side of the models was divided. A random number ranging from 0 to 1 was generated for each lattice. When the number was smaller than a volumetric oil fraction, the lattice was considered to be occupied by oil. The oil in the lattices connected with the surface lattice on a side or a plane in the two- and three-dimensional models was assumed to be extractable. In both the models, the surface oil content was lower when the oil content was lower in the solid microcapsules, especially when the No values are larger (smaller oil droplets). The simulation suggested that the smaller droplets were more favorable for the production of microcapsules wherein the oil was hardly oxidized. The effect of the formation of central voids in the microcapsules on the surface oil content was also examined. The formation of larger voids made the content larger, although this effect was not significant.
In this study, muscle protein gel-formation during fermentation by lactic acid bacteria at 4℃ was investigated using myofibrillar protein as a model gelation system. Protein fermentation by the two strains of psychrotrophic lactic acid bacteria Lactobacillus sakei D-1001 and Lactobacillussakei No. 4 was performed at 4℃. Physical properties and microstructure of gels were examined after treatment at 70℃ for 30 min. Both myofibrillar protein gels showed higher gel strength and syneresis rate than non-fermented gels. Whereas protein distributions did not significantly differ between fermented and non-fermented gels, a finer strand-like microstructure was more apparent in fermented gels.