Brown rice has various health benefits; however, it is more difficult to cook and has a harder texture as compared to milled rice. In this study, the effect of the sous-vide cooking method on starch retrogradation and textural properties of brown rice was investigated by comparative analysis with conventionally cooked brown rice based on moisture content assay, evaluation of the textural property analysis, and differential scanning calorimetry (DSC). The results of the study are as follows: First, the moisture content of sous-vide cooked brown rice was higher than in the conventionally cooked brown rice. Second, the sous-vide cooked brown rice has lower hardness, higher adhesiveness, and lower retrogradation enthalpy during storage than conventionally cooked brown rice. Finally, the retrogradation properties of cooked brown rice during storage were analyzed by DSC. The enthalpy increased more rapidly in the case of conventional cooked brown rice, reaching 1.58 J/g after 3 days of storage. This indicated that sous-vide cooking is effective in preventing retrogradation of rice during storage.
In this study, baked rice donuts with added psyllium seed husk were manufactured and their quality and retrogradation characteristics were investigated. Control (Con) was made only with wheat flour; Psyllium seed husk in the amount of 8, 12, 16 and 20 grams was added to make rice donuts (P8, P12, P16 and P20). Higher amounts of psyllium seed husk reduced the moisture loss and baking loss, and increased the moisture content and water holding capacity of the donuts. The specific volume of Con was the highest of all the groups. As the amount of psyllium seed husk increased, the lightness and yellowness of the crumb decreased, and the redness of the crumb increased. Hardness also increased as the amount of psyllium seed husk increased. The hardness of P16 was the most similar to that of Con. The scanning electron microscopy images also identified that the structure of the donuts got denser as the amount of psyllium seed husk increased. Rate constant (k) of the rice donuts with psyllium seed husk were lower than that of Con. In conclusion, it is considered that P16 is the sample that is the most similar to Con in terms of texture, but the retrogradation was more retarded in P16 than Con.
The experiments were carried out to elucidate the varietal variation of retrogradation in aged cooked rice and its association with some physicochemical properties of milled rice. The fifteen rice materials were selected from forty-three low-amylose japonica and Tongil-type rice cultivars based on palatability and retrogradation of cooked rice stratified by preliminary sensory evaluation of warm and cooled cooked rice. One japonica glutinous rice variety was included for comparison of retrogradation of cooked rice. The α -amylase-iodine method was adopted for checking the varietal difference in retrogradation of cooked rice. The desirable checking time for evaluating the varietal difference in deterioration of aged cooked rice was four hours after storing in room temperature and two hours after preserving in refrigerator based on the largest coefficients of variations in degree of retrogradation of cooked rice. The rice cultivars revealing the relatively slow retrogradation in aged cooked rice were Ilpumbyeo, Chucheongbyeo, Sasanishiki, Jinbubyeo and Koshihikari. A Tongil-type rice, Taebaegbyeo, and a japonica cultivar, Seomjinbyeo, showed the relatively fast deterioration of cooked rice. The retrogadation index represented by the percentage of retrogradation difference between warm and cooled cooked rice to original estimates of warm cooked rice was significantly affected by the degree of retrogradation of cooled cooked rice. Generally, the better rice cultivars in eating quality of cooked rice showed less retrogradation and much sponginess in cooled cooked rice. Also, the rice varieties exhibiting less retrogradation in cooled cooked rice revealed higher hot viscosity and lower cool viscosity of rice flour in amylogram. The sponginess of cooled cooked rice was closely associated with magnesium content and volume expansion of cooked rice. The hardness-changed ratio of cooked rice by cooling was negatively correlated with solids amount extracted during boiling and volume expansion of cooked rice. The major physicochemical properties of rice grain closely related to the palatability of cooked rice may be directly or indirectly associated with the retrogradation characteristics of cooked nce. The varietal difference in retrogradation of cooked rice can be effectively classified by scatter diagram on the plane of upper two principal components based on some retrogradation properties of cooked rice. The deteriorated structural change in cooled cooked rice by observing through the scanning electron microscope was more conspicuous in the fastly retrograded cooked rice than in the slower one.