Disintegration of steamed root tissues was investigated using cultivars and breeding lines having various textures, and the contents of starch, pectic substances and calcium in the raw roots were analyzed. The steamed roots of cultivars and lines with high starch content showed a mealy texture and low degree of tissue disintegration. The 5 groups of roots, categorized by texture in reference to a standard cultivar (Kokei 14), were classified into 3 or 4 significantly different (p < 0.05) groups based on starch content. The disintegration-rate of steamed root tissue, expressed by the rate of weight decrease after agitation in water by shaking, was correlated with texture; textural differences could also be attributed to the degree of disintegration, particularly for roots with moderate starch content (16-22.5%). The disintegration-rate of steamed root tissue indicated a negative correlation (r=-0.403) with fresh weight Ca content per root, which could not account for the textural differences. The disintegration rate also showed a weak negative correlation (r=-0.214) with the content of chelating agent-soluble pectic fraction extracted from starch residue. In summary, the disintegration rate of steamed root tissues was associated with their texture, which largely depended on starch content; and the rate was equally related to Ca and starch contents via interaction with chelating agent-soluble pectic substances.

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This study examined the effects of drying methods on the generation of flavor compounds in “Karebushi.” First, in order to obtain the primary mold culture product, Eurotium repens (YM-1418) was sprayed on the surface of “Hadakabushi” and cultured for two weeks. The samples were then dried either under the sun or by a machine (dehydrator). Subsequently, the samples were cultured for another week to produce a secondary mold culture product. The flavor compounds of samples were analyzed using GC-MS. Forty major flavor compounds were identified, and among these compounds, hexanal, heptanal, and octanal were quantified. Results indicated that the different drying methods led to the generation of different flavor compounds, especially of aldehydes. Furthermore, in comparing the sun-drying and machine-drying methods, the former increased hexanal and heptanal, and the extent of these increases was proportional to the duration of sun-drying. We also identified that the production of these aldehydes increased when drying during spring and summer. Next, the increase of these aldehydes was clarified by the UV irradiation test. We revealed that the sun’s UV rays were mainly responsible for the remarkable increase in hexanal and heptanal during the “Karebushi” manufacturing process.

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In order to prevent spoilage of okara, a by-product of tofu manufacturing, the use of lactic acid fermentation was investigated. Lactobacillus casei L-14 and Weissella paramesenteroides HM25 were selected as starter cultures of okara fermentation. The optimum fermentation conditions, such as inoculum levels and mixing ratios, of the two lactic acid bacteria (LAB) were determined in order to realize rapid LAB growth and high organic acid levels in the okara. When okara was inoculated with 10⁶cfu/g mixed LAB and incubated at 30°C for 7 days, almost no microorganisms except for the LAB inoculated were detected in the okara. However, okara contaminated with large numbers of microorganisms at the tofu manufacturers and fermented under identical conditions showed significant numbers of bacteria, especially spore-formers. Therefore, semi-anaerobic incubation was attempted to effectively prevent okara spoilage. Okara was inoculated with mixed LAB and then packaged into airtight containers at 0.92kg/L. After 7-day incubation, no spore-forming bacteria, coliforms or fungi were detected in the okara. These results indicated that the combination of mixed LAB and semi-anaerobic incubation using airtight containers were effective in preventing the spoilage of okara.

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The dynamics of radioactive cesium (¹³⁴Cs plus ¹³⁷Cs) during rice cooking were investigated to examine the effect of rice bran removal ratio on the distribution of radioactive cesium in the cooked rice fraction. The removal ratios of bran used in this study were 0, 30, 50, 70, and 100%. The radioactive cesium in brown rice, pre-cooked rice, cooked rice and washing water were measured with a germanium semiconductor detector. Processing factor (Pf, ratio of radioactive cesium concentration in processed materials to raw materials) and food processing retention factor (Fr, ratio of radioactive cesium content in processed materials to raw materials) were calculated. The Pf values for cooked brown rice and cooked polished rice were 0.43 and 0.25-0.26, respectively; and the Fr values for cooked brown rice and cooked polished rice were 0.95 and 0.62-0.64, respectively. Both Pf and Fr values for cooked brown rice showed significantly higher levels than those of polished rice; however, the increase of removal ratio from 30% to 100% had no significant effect (p<0.05) on Pf and Fr values for cooked rice. From these results, rice polishing contributes to the removal of radioactive cesium during rice cooking; however, differences of bran removal ratio, even from 30% to 100%, had little effect on the dynamics of radioactive cesium during rice cooking.

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Plant origin lactic acid bacteria from “Sunki”, pickled red turnip without salt, a traditional lactic acid fermented food from the Kiso area of Nagano Prefecture were isolated and employed in the development of yogurt. For that purpose, screening tests were carried out to obtain lactic acid bacteria utilizing lactose and curdling milk. Consequently, strains T998, L204, and L205, which produced yogurt without added ingredients for the growth of plant origin lactic acid bacteria except milk, were isolated. The strains were identified as Lactobacillus paracasei (T998, L204) and Lactobacillus buchneri (L205). L204 and L205 in combination, but not alone, could produce yogurt. T998 and the combination of L204 and L205 were each applicable for the commercial production of yogurt as single starter cultures of lactic acid bacteria isolated from “Sunki”.

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Two topics related to the physical properties of foods and associated water effects were reviewed: the physical properties of hydrocolloids and care foods for dysphagic patients, and the water sorption and glass transition of foods. The percolation model effectively described the behavior of the rheological properties of food hydrocolloids near the sol-gel transition point relating to polymer network structure. The rheological properties of food hydrocolloids influence the velocity of the bolus. For thickener solutions, viscosity (μ), dynamic viscosity (η'), and complex viscosity (η^*) are well correlated with the maximum velocity through the pharynx, V_max, and are thus considered to be suitable indices of liquid-type foods for patients with dysphagia. For gels, the decrease in V_max was slightly above the concentration of the sol-gel transition point. Water sorption isotherms provide information on the interaction between water and solid components in foods. Water sorption isotherms of foods can be fitted by the GAB equation. Using solution thermodynamics, the partial molar quantities of both water and solutes can be estimated from water sorption isotherms. The concept of glass transition can explain many phenomena such as the reaction rate of non-enzymatic browning and powder caking. Glassy materials change to the rubbery state at T_g. The value of T_g for those materials decreases with increasing water content due to the plasticizing effect of water. The difference in the chemical potential of solid (adsorbent) between a solution and a pure solid, ΔG_a^s, which was obtained from water sorption isotherms by solution thermodynamics, was correlated with the depression of the glass transition point ΔT_g.

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The thermal behavior, structure, and dynamic properties of water confined in polymer gel Sephadex G15 were investigated over a temperature range of 298-173K as a function of hydration level (g H₂O/g dry gel) by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and quasi-elastic neutron scattering (QENS) and neutron spin echo (NSE) measurements. The DSC data showed that there are three states of water in G15 gel: free water, freezable bound water, and unfrozen water. The X-ray radial distribution functions revealed that the tetrahedral-like hydrogen bonded network of confined water is largely distorted, compared with the bulk water. The QENS data showed that the water molecules perform local motions characterized by a diffusion coefficient of (0.65±0.05)×10^-5cm²s^-1 within a sphere with a radius of 4.4 Å. The Arrhenius plots of the relaxation time of water gave an activation energy of 44.2±1.5 kJmol^-1, which is somewhat larger than the value of 15-36kJmol^-1 of capillary condensed water confined in mesoporous silica MCM-41 C10 (pore diameter 21 Å). The present findings suggest that water molecules in G15 gels are strongly bound to the hydroxyl groups of the gel matrix.

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