Mass transfer is important in many food processes such as drying, extraction and cooking. In many cases such processes are governed by diffusion. Here, we first discuss on diffusion coefficients at dilute solutions by explaining the definition of the diffusion coefficient. Then, the diffusion coefficients in gel are discussed. The self-diffusion coefficient and the mutual diffusion coefficient are also explained. Thirdly, the diffusion coefficients at concentrated and supersaturated solutions are reviewed. As a good illustrative example, a sucrose-water system is chosen. The diffusion coefficient decreases with decreasing water concentration sharply, especially below 0.3 kg-water/kg-total, where the solution becomes supersaturated. The activation energy for diffusion increases from 20 kJ/mol in this supersaturated solution region. The desorption isotherm and the isosteric heat of adsorption data also show that the water in this region is strongly bound to the solute. Desorption behavior of water from gelled sugar solutions can be grouped into two categories. Gelled sugar solutions in one category such as agar-gels were not affected by the gel properties and the diffusion in sugar solutions is dominant. On the contrary the desorption of water from gelled sugar solutions such as gelatin was governed by the surface properties of dense gel layers near the surface. The importance of the effect of the surface concentration and the concentration distribution on the desorption curve is discussed. The drying behavior of sugar solutions based on the water concentration dependent diffusion coefficients is explained with emphasis on the flavor retention due to the selective diffusion.
Progress of retrogradation of rice grain which was cooked by microwave heating was evaluated using X-ray diffraction (XRD) method. Cooked rice grains were not powdered but made to paste and measured directly. A lot of samples were able to be measured by this convenient method. The polarization microscopy was also conducted for visualization of retrogradation. The differences in retrogradation observed by XRD were found between rice grains in the cooking container like differences in cooking properties such as moisture content and degree of gelatinization. Progress of retrogradation was observed after 12 hours from beginning of storage at 5℃. Using Avrami equation, kinetic parameters of retrogradation were calculated. Rate constant of retrogradation was greatly affected by moisture content of cooked rice grain. In the case of low moisture content gave a high rate constant for retrogradation.
A drying model was developed to simulate changes in the water content and the temperature of a cylindrical plant material, tobacco midrib, which expands in air flow mixed with or without superheated steam. The model is characterized as follows: (1) mass and heat transfers in the midrib are described by one-dimensional diffusion based on conservation laws; (2) adsorption equilibrium of water is always achieved at a solid-gas interface, so that the internal movement of water is regulated as a rate-limiting step; and (3) transfer phenomena in the expanding diffusion field are simplified by defining the expanded maximum radius as a diffusion length. The curves of water content and temperature calculated by the model were in agreement with each experimental value under various drying conditions: air temperature of 373 to 473 K and flow rate of 10 to 20 m/s. The model also represented drastic rises in temperature caused by condensation heat of water vapor in the initial drying stage. It was therefore judged that the model has validity and can be applied to estimation of the drying curves in expanding diffusion systems for tobacco midribs.
Recently, Most consumers concern for safety and relief to the products and this tendency is remarkable to the food products. Once serious defect of the products is detected in the market, company must search all detected objects. So traceability performance is very important for beverage products company. Additionally, company should take responsibility for the products, therefore accountability that proves products safety is also important. For these reasons, our company has already introduced some systems for traceability and accountability. These systems help us to know what kinds of materials are used in the products and when the products proceed through each equipment in the factory, but these systems can't identify “a bottle product” because of system mechanism. It is very difficult to recognize “a bottle product” because manufacturing conveyer line is too complicate and speedy in real situation. To solve this problem, we introduce new systems with character recognizing technique. The new systems enable us to identify “a bottle product” and to improve accuracy and speed over 92% compared with previous ones. According to the new systems, we can provide more detailed and complicated information to consumers. As a result, both quality assurance level and company values can be raised.
Current reports show that various researchers are investigating methods for the formation of silk fibroin films from the Bombyx mori silk worm. In this study, we investigated four factors involved in insoluble fibroin film formation. These factors were glycerol concentration, drying conditions including temperature and humidity, and pH. Addition of under 0.05 v/v% glycerol to the fibroin solution led to soluble films, whereas glycerol concentrations of up to 0.10 v/v% produced insoluble films. At temperatures and humidity of up to 30℃ and 70% RH, respectively, the film was insoluble. In terms of the effect of pH on insoluble fibroin films, at pH <11 the fibroin film did not dissolve. At fibroin concentrations of 2~10 mg/mL the films did not dissolve, and the requirement for insoluble film formation was >2 mg/mL fibroin. From these results, the factors involved in insoluble fibroin film formation are a glycerol concentration of 0.10 v/v%, drying conditions of up to 30℃ and up to 70% RH, pH < 11 and a fibroin concentration of >2.0 mg/mL.
The effect of reconstituted emulsion oil-droplet size of the microencapsulated flavor on its release from the spray-dried powder was investigated under boiling condition at atmospheric pressure. The wall materials of use were maltodextrin, highly branched cyclic dextrin, resistant starch, or a mixture of these materials. Gum arabic, modified starch (HI-CAP or CAPSUL) or soybean soluble polysaccharides was added as an emulsifier. The core material comprised d-limonene as the model flavor, medium chain triacylglycerol, and sucrose acetate isobutyrate at five different mixing ratios by which the density of the core material was varied. The release mechanism obeyed first-order kinetics and the release rate constant depended mainly on the reconstituted emulsion oil-droplet size of the microencapsulated flavor in the spray-dried powder.