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    Pore structure in food: Simulation, measurement and applications
    (Springer New York, 2013) Gueven A.; Hicsasmaz Z.
    Influence of microstructure on process rates and product texture is widely accepted. Simulation of the pore structure of various food materials and numerous food processes has attracted recent attention in the food literature. Several approaches have been applied to predict transport phenomena in food materials. The first one is the continuum approach in which all the microscopic complexities are lumped into effective diffusivities in which diffusivities are empirical constants. Simulation of the characteristic pore structure depends on accurate quantitative data on the pore size distribution. Qualitative three-dimensional (3-D) imaging techniques such as X-ray micro-tomography and magnetic resonance imaging (MRI), and two-dimensional (2-D) imaging techniques such as scanning electron microscopy (SEM) and transmission electron microscopy are used to analyze the cell structure. X-ray microtomography and MRI are 3-D non-invasive techniques that allow reconstruction of the pore structure, but the sophisticated procedure complicates combining the restructured model with transport equations. Mercury porosimetry and liquid extrusion porosimetry are used for quantitative evaluation of the cell structure. Drawback of porosimetry is: Laplace-Young equation of capillary flow dictates that the intruded/extruded pore diameter is inversely proportional with capillary pressure. Thus, cell size distribution from intrusion/extrusion data is erroneous since the assumption that pore sizes regularly increase/decrease as intrusion/extrusion advances is not physically true. A mathematical model that simulates experimental intrusion/extrusion curves by randomly distributing different cell sizes within a geometric unit cell remedies this drawback. Such a model is called a geometric network model, and is the second approach that can be used to simulate the pore structure and transport phenomena through the porous medium. Geometric network models used in petroleum reservoir engineering, soil science, and catalysis are for relatively low porosity materials (porosity B 0.4). Food materials generally have high porosity (0.5-0.9), thus direct application of geometric network models to foods is difficult. There are very few applications of geometric network models to food materials. 1-D approaches have been applied to simulate the pore structure of food materials, and 2-D approaches have been applied to simulate the rehydration and reconstitution of ready-to-eat foods. Herein: The importance of the pore structure in terms of food processing and product quality is emphasized; methods of obtaining accurate data on the pore structure of food materials are described; advantages and drawbacks of several available predictive mathematical models are presented; and how the geometric network model can be used to predict the pore structure and transport through porous food materials is described. © Alper Gueven and Zeynep Hicsasmaz 2013. All rights reserved.
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    Soy plant tissue culture as an alternative for isoflavonoid production
    (Nova Science Publishers, Inc., 2012) Gueven A.; Hicsasmaz Z.
    Soybean (Glycine max.) is popular due to health consciousness, mad cow disease and high meat prices. Soybean consumption ranges between frozen green soybeans to cold cereals, non-dairy cheeses and desserts, milk and yogurt alternatives. Soybean is a source of edible oil, and the residual meal is used as a protein supplement for livestock. Soybean lipids are cholesterol-free. Soybean consists of 15 % dietary fiber and its protein content is between 36-46 %. Soy protein contains all essential amino acids. It has superior functional properties and is therefore a replacement for animal proteins in non-diary alternatives and meat analogs. Soybeans are the most abundant source of isoflavones. Isoflavones are anti-atherosclerotic; they decrease risk of coronary disease, improve body composition and prevent hormone-dependent cancers. Plant cell cultures are attractive alternatives for secondary metabolite biosynthesis. Plant tissue cultures offer production of phytochemicals independent of geographical, seasonal and environmental factors. They ensure continuous production with uniform quality and yield. Cell growth in plant tissue cultures and secondary metabolite biosynthesis are correlated, but there also exist non-growth-related secondary metabolites. Chemical and physical stresses trigger biosynthesis of secondary metabolites. First, the best metabolic stress that triggers secondary metabolite biosynthesis is found. Then, optimum conditions needed in a bioreactor are investigated. Scale-up problems arise due to oxygen and nutrient transfer. Agitation to increase mass transfer rates cause death of the cells due to shear. Thus, airlift bioreactors are recommended for plant tissue cultures. The next handicap is the recovery of secondary metabolites, especially when they are intracellular. Effects of various chemical and physical stresses on cell growth and isoflavonoid biosynthesis by the soybean callus suspension culture have been investigated. Methyljasmonate was effective in triggering isoflavonoid biosynthesis. Pulsed electric field (PEF) is promising for bioreactor applications, since PEF not only performs as stress to induce biosynthesis, but it also is an agent of intracellular secondary metabolite excretion and recovery. Influence of biotic stress on isoflavonoid production by the soy plant cell culture has also been highlighted. Effect of immobilization on the growth of soy plant cell cultures and isoflavonoid biosynthesis has been studied on pilot scale bioreactors in conjunction with innovative engineering solutions for product recovery. However, efforts to extend results of small scale fermentations in flasks to a semi-continuous airlift bioreactor system were not very successful. Shear stress during aeration prevented the cells from staying in aggregate form. Detailed optimum engineering solutions are required to enable continuous production of secondary metabolites using plant cell cultures and will continue to be a challenging issue during the beginning of the twenty-first century. © 2013 Nova Science Publishers, Inc. All rights reserved.