Some topics related to physical properties of foods and effect of water on them were reviewed. The freeze-drying of liquid foods can be analyzed by a modified URIF (Uniformly Retreating Ice Front) model below the sample temperature of Tg', the glass transition temperature for CAS (Concentrated Amorphous Solution) in frozen low-concentration material. If sample temperature increases above Tg' during freeze-drying, CAS in the frozen sample is in the rubbery state. The CAS in the rubbery state may collapse during freeze-drying and block the path of vapor, which makes it difficult to remove water from the sample. Water sorption isotherms give information on the interaction between water and solid components in foods. Using solution thermodynamics, the thermodynamic parameters of both water and solutes can be estimated. The integral Gibbs free energy, ΔGs, is considered to be a suitable parameter for evaluating the interaction between solid and water from the thermodynamic point of view. The thermodynamic parameters obtained from water sorption isotherms relate to the degree of reduction in the glass transition temperature (Tg), accompanied by water sorption. The difference between the chemical potential of solid (adsorbent) between a solution and a pure solid, ΔGas, which is obtained from water sorption isotherms by solution thermodynamics, is correlated with ΔTg (≡Tg − Tg0; where Tg0 is Tg of dry material). This indicates that plasticizing effect of water on foods can be evaluated through the parameter ΔGas. The relaxation time τ obtained from the dielectric relaxation is also considered to be suitable parameters for the characterization of the plasticizing effect of water on a glassy material. The percolation model effectively described behavior of the rheological properties of food hydrocolloids near the sol-gel transition point. The maximum velocity through the human pharynx, Vmax, which is obtained by the ultrasonic pulse Doppler method, is considered to be a good predictor of aspiration risk for patients with dysphagia. For a gelling agent, Vmax decreased with the increase in concentration; the decrease was slight above the concentration of the sol-gel transition point.
Yukimuro means “snow room” in Japanese and has been used to preserve vegetables and other foods under low temperature by using natural energy. Here we investigated the effectiveness of snow utilization for the storage of wheat flour. Strong and whole grain flours were packed into paper bags and stored for three months under three different conditions: at room temperature, in a cold refrigerator, and in a moist cold snow room (i.e., yukimuro) and provided for analyses. As compared with the samples stored at room temperature, both cold storage in refrigerator and moist cold storage in snow room reduced lipid peroxidation and generation of free fatty acid. The wheat flours stored in yukimuro showed better bread-making properties than those stored at room temperature or in refrigerator. The brown bread made from the flours stored in yukimuro showed better sensory evaluation scores. These findings indicate that moist cold storage in snow room (yukimuro) suppresses lipid oxidation and improves bread-making properties of wheat flours.
Plant factories daily produce large amount of high quality vegetables under artificially controlled environments. One of the important issues to be considered is to establish suitable storage systems to achieve an acceptable length of shelf life and to minimize the risk to foodborne illnesses. This study deals with the application of the supercooling technologies (cooling below the freezing point without phase change) to the extension of the shelf life of the high quality leaf lettuces produced by the plant factories. The followings were found through the experimental study. The freezing temperature of the leaf lettuces of the plant factories is around -0.2℃ and the nucleation temperature of the leaf lettuces is between -1.0℃ and -6.1℃. The type of packages affects the characteristics of the supercooled lettuce by controlling the cooling rates and to reduce the risk of being frozen in the supercooled state. It was also shown that the lettuces under supercooled conditions keep the initial state of the water and sugar contents by reducing the respiration rate, and that the risk of foodborne illness is improved by keeping the number of the bacteria in low level even after the supercooled storages for three weeks.
Volatile sulfur compounds are very important in the contribution or sensory analysis of flavors in many foods. The molecular inclusion of flavor in cyclodextrin (CD) is one technique to protect against the degradation of labile flavor. Encapsulation of diluted allyl sulfide in middle–chain triglyceride (MCT) oil with cyclodextrin as a wall material was investigated using a spray dryer. A carrier solution was prepared by dissolving α–, β–, or γ–CD in distilled water. Allyl sulfide (10,000 ppm) in an MCT and CD solution was homogenized and incubated at 30℃ for 8 h. This incubated solution was spray dried in a mini spray dryer. Spray–dried powder containing allyl sulfide was obtained with an allyl sulfide content of 0.78 mg/g CD for α–CD, 0.17 for β–CD, and 0.63 for γ–CD at an inlet air temperature of 200℃. The content of allyl sulfide in the powder was affected by the concentration of allyl sulfide in the MCT oil and the content of MCT oil in the feed solution. The inlet air temperature did not affect the content of allyl sulfide in the CD powder. The incubation of allyl sulfide in the MCT oil and CD solution formed an inclusion complex of allyl sulfide in the CD powder. It was also shown that the lettuces under supercooled conditions keep the initial state of the water and sugar contents by reducing the respiration rate, and that the risk of foodborne illness is improved by keeping the number of the bacteria in low level even after the supercooled storages for three weeks.
Progressive freeze-concentration (PFC) of blueberry juice was carried out by a tubular ice system and the original juice at 11.2 Brix was concentrated up to 27.2 Brix. The PFC-concentration was proved to give a high quality concentrate with no substantial change both in organic acid distribution and flavor profile. The PFC-concentrated blueberry juice was fermented to produce a blueberry wine with 11.1 vol-% alcohol content, showing that a high alcohol content can be obtained without chaptalization in the present method. After the fermentation, some changes were observed both in the organic acid distribution and the flavor profile. As a whole, however, the blueberry wine retained enough amount of original blueberry flavors. The present results suggest a possibility to produce a new-type blueberry wine with rich ingredients and flavors.
Release rates of d-limonene from spray-dried powders were investigated for various wall materials such as maltodextrin (MD) (dextrose equivalent (DE)＝25 and 19), α-lactose, and sucrose. Spray-dried powder of d-limonene emulsified with hydrolyzed whey protein was prepared with the solid content of 60 wt% and containing 53.9 wt% d-limonene and medium chain triglyceride (MCT) oil (weight ratio (d-limonene/MCT oil) of 0.20), 35.7 wt% carrier solution with wall material, and 7 wt% hydrolyzed whey protein. The release rate of d-limonene from the spray-dried powders was measured under storage conditions with constant temperature of 50℃ and maintained at different relative humidity (RH). The release rate of d-limonene increased at higher RH and was significantly dependent on the wall material. Logarithm of release rate constant was proportional to RH for spray-dried powders of lactose and MD (DE＝25 and 19) above 68% RH.
The number of occurrences of foreign objects in food is becoming less frequent. However, it is very difficult to remove small foreign objects such as hair and soft plastics in food. In this paper, the results of an experimental study of the performance of a new electrostatic separator of small foreign objects in dried food are presented. The separator consists of an inclined rotating drum, which is grounded, a cylindrical electrode fixed at the center of the drum and a suction device. The principle of the separation is based on the difference in the charge per unit mass of the dried food and foreign objects. Separation tests were performed on two types of mixtures. The effects of operating parameters, such as the applied voltage and the angular speed of the drum, on the separation efficiency were examined. In the separation of a mixture of plastic fragments and dried lettuce, the recovery rate of the lettuce was greater than 96% for a purity of 100%. In the separation of a mixture of hairs and dried lettuce, the recovery rate of the lettuce was greater than 94% for a purity of 100%.
Intake of probiotics is effective in the development of intestinal flora. Generally, addition of living microbes to the intestine is important for the regulation of the intestinal functions and growth inhibition of pathogenic bacteria. However, probiotics such as lactic acid bacteria do not always survive in the stomach. Lactic acid bacteria are useful as a probiotic, thus their death in the stomach decreases their beneficial effects. Konjac is an indigestible high-fiber food. In the present study, we examined the effect of konjac on the survival of lactic acid bacteria. Lactobacillus crispatus and Lactobacillus plantarum strains were taken to globular konjac, which had large surface area by including bubble. Subsequently, the konjac was soaked in artificial gastric juice（pH 1.2）. The lactic acid bacteria without konjac survived when incubated for 30 min but not 60, 90, or 120 min, whereas L. crispatus and L. plantarum with konjac survived even when incubated for 60 and 120 min, respectively. Therefore, the present study suggests that the survival of lactic acid bacteria improves on co-incubation with konjac. In addition, the probiotics may be able to access the intestines regardless of the kind of bacterial species.
This study focused on the processed food products, using raw okara (a food product developed to mitigate problems associated with mass disposal of soy waste). To examine the heating condition effectively, we simulated food qualities during heating. Color change was treated as a first-order reaction, and kinetic parameters (Ea = 61.6 kJ/mol，Z = 4.93×105 1/s) were calculated by Golden section method. Moisture content was calculated via mass transfer analysis, based on Fick’s laws of diffusion. Our simulation predicted values for color, moisture content, water activity, and texture that were in good agreement with experimental values. We determined that, to achieve an equivalent to a commercial product, it was suggested that about 1/2 could shorten heating time by changing surface temperature from 80℃ to 120℃. Thus, this simulation technique can contribute to the shortening of heating times for processed food products.
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