Food is essential to life. The traditional and distinctive types of foods have been maintained and provided over many centuries in every country in the world. During recent years, processing technology has been developed for manufacturing a wide range of foods, and meanwhile many investigations on the rheology of foodstuffs have been made by scientists in the various academic disciplines. This article reviews the original works on rheology and texture of foodstuffs published by Japanese authors, and integrates advances made in areas of food science and technology in Japan. The contents are divided into four sections; some interpretations of food texture, rheological characteristics of traditional Japanese foods, progress in methods of rheology in allied fields, and international correlations in research activities on the rheology of foodstuffs.
Soups were made from three chemically double-modified (hydroxypropylated and cross-linked) wheat starches, and their physical properties and sensory attribute were compared with that made from native wheat starch and chemically double-modified waxy maize starches. The pastes of modified wheat starches were lower in pasting temperature, smaller in breakdown, and higher in the viscosity at 50 °C compared with native wheat starch paste. The soups made from highly cross-linked modified starches, W42 and W46, did not change in apparent viscosity and texture properties as well as did not show syneresis upon storing at low temperature and freeze-thaw cycles. Thus, those starches showed high stability at storing low temperature. Viscosities in low order M465, W4, W46 and W42. Sensory evaluation showed that the soups of hydroxypropyl cross-linked starch were preferred in smell, taste, smoothness, easy to swallow, firmness, and overall evaluation. In paticular, the soup (15 °C, 60 °C) of highly double-modified starch, W46, had good smell and taste, and was smooth, easy to swallow, stickiness firmness, and overall evaluation, and it was preferred at all items. M465 was not preferred because of the high viscosity, the low viscosity, and the taste and smell, respectively.
The effects of sodium ion and calcium ion on hardness of rice grains such as Koshihikari, Yukinosei and Akihikari, were investigated using breaking stress and weight uptake measurements, and inner structures of the samples were observed via scanning electron micrographs. When the same rice species was heated in the deionized water, sodium chloride aqueous solution and calcium chloride aqueous solution, the magnitude of breaking stress became higher in a order: the deionized water < sodium chloride aqueous solution < calcium chloride aqueous solution. In the same kind salt solution, the magnitude became higher in a order: Koshihikara < Yukinosei < Akihikari. The value of weight uptake of the same rice grains was larger in a order: calcium chloride aqueous solution < sodium chloride aqueous solution < the deionized water. The circumference structures of rice grains heated in aqueous sodium chloride and calcium chloride solution looked more compact and had finer texture than those heated in the deionized water.
The effects of autoclave and oven treatments on gelatinization properties of rice flour and on crystallite structures of rice starch in rice flour were studied using dynamic oscillatory measurement, differential scanning calorimetry (DSC), X-ray diffractometry, and scanning electron microscopy (SEM). Autoclave-treated rice flour (ATR) and oven-treated rice flour (OTR) were prepared using an autoclave at 120 °C for 60 min and oven at 160 °C for 60 min. Dynamic oscillatory and DSC measurements demonstrated that autoclave treatment modified the gelatinization properties that delayed gelatinization temperature (TG' and To) and decreased in peak storage modulus (G'p). Autoclave treatment caused formation of amylose-lipid complexes and partial gelatinization of starch granules in ATR studied by DSC and X-ray diffractometry. Autoclave-treatment engendered formation of amylose-lipid complexes and partial gelatinization of starch granules in ATR studied by DSC and X-ray diffractometry. Alteration of gelatinization properties of ATR flour is attributed to changes in rigidity of starch granules during treatment. Similarly to ATR, oven treatment was effective for gelatinization properties. Nevertheless, it was insufficient for rearrangement of starch chains in OTR flour.
Consistent thickening sol-style food samples having hardness equivalent to salad oil and plain yoghurt, respectively, were prepared with the use of thickening agents made of mixing starch and guar gum in various composition ratios. The correlation between the viscoelastic behavior of these samples and such sensory values as "ease of swallowing" was studied. An effective way of assessing the "in-mouth sensation" and "ease of swallowing" of these consistent sol-style food samples was to examine the tan δ of the dynamic viscoelasticity of the sample in the linear region, as well as the distortion dependence and, in particular, to study the torque and attenuation status of G' in the non-linear region. The "ease of swallowing" of the samples can be estimated to a certain extent from the G' and tan δ on the low frequency side.
The thermal conduction induced close to the heating plane was detected along the one-dimensional axis (x axis) in foodstuffs such as food models, cereal flour doughs, and highly moisturized foods during pan broiling (heating in a metal vessel) at 105 °C , frying at 180 °C , boiling at 100 °C , steaming at 100 °C , and baking at 170 °C , using the newly provided heating devices. The velocity of increasing temperature monitored in each sample was ranked highest to lowest in the order of frying, boiling, steaming, pan broiling and baking, irrespective of temperature in each heat transfer medium. The increasing temperature vs. heating time curve for all the samples was in conformity to an exponential equation derived from an assumption that a retardation phenomenon plays a role in the thermal conduction. A power relationship was also found in double-logarithmic plots of reciprocal of the retardation time in the exponential equation vs. effective thermal diffusivity α (= λ / Cp ·ρ, where λ is the thermal conductivity, Cp is the heat capacity at constant pressure, ρ is the density) for all the samples. The power coefficient in this relationship describes a distinctive feature of the heating procedures in cooking.
Gomatofu is a mixed gel consisting of kudzu (arrowroot) starch and sesame seeds. In this study the effect of sesame oil contents on the mechanical properties of gomatofu was investigated by rheological measurements under uni-axial compression and creep, SEM observation and sensory evaluation. Huskless (hereafter Muki) white sesame seeds were used. The gomatofu samples are as follows: a) Defatted gomatofu (oil content 0%), b) Defatted gomatofu (oil content 0.42%), c) Control gomatofu (oil content 3.4%), d)3% sesame oil added (oil content 6.4%), e) 6% sesame oil added (oil content 9.4%), were prepared and examined. From the results of the texture measurement, the hardness increased with increasing oil content, but cohesiveness in the sample c), control gomatofu, showed the highest value on the first storage day. Conversely the adhesiveness of the sample c) was the lowest. With increase in the number of storage days, hardness of the sample increased. Cohesiveness and adhesiveness decreased with increasing oil content. From the result of the creep measurement, the coefficient of elasticity and viscosity of 4 elements model increased with the number of storage days. The size of air cells was found to become smaller with increasing content of oil by SEM (scanning electron microscopy) observation. In the sensory evaluation, the control sample c) and the sample d) were highly evaluated for total acceptance. From these results it was found that favorable oil content was 3.4˜6.4 % in the sample (gomatofu). The correlation between mouthfeel and oiliness (0.47, P<0.05), and between mouthfeel and total acceptance (0.94, P<0.001) of the sensory evaluation showed significant difference.