Influence of Sulfur and Nitrogen Content of Rice Grains on Flavor in Stored Sake

The influence of nitrogen and sulfur compounds in rice grains on changes in flavor in stored sake was investigated using Japanese rice cultivars for sake making. Nitrogen content exhibited a significant positive correlation with sulfur content. Based on the molar ratio of nitrogen to sulfur in the rice grain, the sulfur compounds appeared to be derived from protein‐associated sulfur‐containing amino acids, as reported previously. The higher the protein content of the rice, the greater the amount of nitrogen and sulfur compounds found in both the digest of steamed rice grains and in the sake. Physicochemical changes were investigated in the stored sake to confirm the influence of total sulfur content. Polysulfides in the stored sake appeared to be higher when made from rice grains of high total sulfur content. Staling of stored sake was affected by levels of protein‐associated sulfur‐containing amino acids in the rice.     

Effect of Germination on Flavor Volatiles of Cooked Brown Rice

The effect of germination on flavor volatiles of cooked brown rice among three different rice cultivars was investigated using the headspace solid‐phase microextraction method combined with gas chromatography‐mass spectrometry. The results showed that some flavor compounds varied significantly throughout the germination process and others did not show distinct changes. The amount of total volatiles, most lipid‐oxidation products, and phenolic compounds decreased in the initial stage of germination but increased significantly at a later stage. The amounts of ethanol and ethyl acetate increased significantly in the initial stage of germination and maintained almost the same levels during further germination. The amount of dimethyl sulfide increased significantly during germination; it showed the most significant change among all volatile compounds.     

Physicochemical Characteristics of Chalky Kernels and Their Effects on Sensory Quality of Cooked Rice

Physicochemical characteristics of chalky rice kernels were compared with those of vitreous kernels, and the effects of chalky kernels on sensory quality of cooked rice were investigated. Chalky kernels were compared with vitreous kernels using image analysis and amylose contents. Because cooked rice is prepared through soaking and cooking, the changes in water absorption index (WAI) during soaking (15, 30, 60, and 90 min) and the structural changes during cooking (0, 3, 6, and 9 min) in chalky and vitreous kernels were investigated using image analysis and scanning electron microscopy. The effects of various proportions (0, 4, 6, 8, 10, and 15%) of chalky kernels on sensory quality of cooked rice were also studied. The chalky kernels tended to be smaller in kernel area, maximum diameter, minimum diameter, and perimeter than vitreous kernels. Amylose content in chalky kernels was slightly lower than that in vitreous kernels. WAI of chalky kernels was higher than that of vitreous kernels. The effects of chalky kernels on the sensory quality of cooked rice were not significant unless the proportion of chalky kernels was ≥15%. A sensory panel agreed that the overall sensory quality of cooked rice with 15% chalky kernels was the lowest among the samples tested.     

转Bt基因水稻"克螟稻"淀粉食用品质与稻米营养成分的研究

对转Bt基因抗虫水稻（Oryza sativa subsp.japonica）与原亲本的淀粉食用品质和稻米关键性营养成分进行了检测与比较,发现这两种水稻在表观直链淀粉含量、胶稠度和淀粉粘滞特性等淀粉食用品质方面基本相同;在粗蛋白、粗脂肪、总灰分、氨基酸和矿物质等关键性营养成分上差异不显著.表明在水稻遗传转化操作过程中T-DNA（Transferred DNA）并未改变原亲本的品质性状.     

Aroma of Cooked Rice (Oryza sativa): Comparison Between Commercial Basmati and Italian Line B5-3

Selected lines of aromatic rice from American cv. A301 were cultivated in Italy, and the agronomic traits and chemical properties related to their aroma were studied. The most characteristic compound responsible for aromatic rice, 2-acetyl-1-pyrroline, was quantified in all lines. Line B5-3, characterized by high 2-acetyl-1-pyrroline content, was investigated in greater detail for its volatile components and was compared with a commercial Basmati rice. Volatiles were collected by steam-distillation. Several classes of compounds were identified and quantified in both samples, including hydrocarbons, aldehydes, alcohols, ketones, heterocyclic, terpenes, disulfides, and phenols. Hexanal was the most abundant compound in both samples, followed by pentanal, 2-acetyl-1-pyrroline, hexanol, benzaldehyde, oct-1-en-3-ol, 4-vinylguaiacol, indole, and trans-2- nonenal. 2-Acetyl-1-pyrroline was present at 570 and 2,350 ppb in Basmati and B5-3, respectively.     

Starch Retrogradation in Cooked Pasta and Rice

Effect of cooking time on starch retrogradation and water distribution was studied in pasta (spaghetti) and rice (parboiled and arborio) using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) Optimum cooking times (OCT) were 8, 16, and 18.5 min for spaghetti, parboiled, and arborio rice, respectively. Swelling was observed by image analysis. OCT spaghetti and rice showed various starch retrogradation rates at various aging times and temperatures. Based on the classical Avrami function, the retrogradation rate at 5°C followed the order spaghetti > parboiled rice > arborio rice, while extent was in the opposite order. At higher temperature (20°C), the rates decreased by 20× in all cases. Thermogravimetric analysis (TGA) investigations were undertaken to check the distribution of water within these products and its relationship to starch retrogradation. During heating, water was released in two distinguishable steps at ≈80 and 100°C. Results supported the conclusion that the more tightly bound water might not participate or facilitate starch retrogradation. In this study, the overall water content did not change during storage, and water appeared to migrate from sites of stronger binding to sites of weaker binding. The temperature dependence of the Avrami constant was described with the Vogel‐Tamman‐Fulcher empirical expression.     

Quality Prediction of Rice Flour by Multiple Regression Model with Instrumental Texture Parameters of Single Cooked Milled Rice Grains

The purpose of this study was to develop highly accurate regression models with texture parameters of cooked milled rice grains for predicting pasting properties in terms of quality index of rice flour. Two methods were adopted as the texture measurement to acquire predictors for the models. In the calibration set, all the multiple regression models by a single‐grain method exhibited a higher R² than those by a three‐grain method. Each of the former models also showed a lower SEP and a higher RPD in the validation set. The prediction performance was best for consistency (RPD = 2.4). The single‐grain method was more advantageous for the pasting prediction. These results suggest that the models based on grain texture could predict rice flour quality.     

Effects of Postharvest Processing on Texture Profile Analysis of Cooked Rice

The effects of drying conditions, final moisture content, and degree of milling on the texture of cooked rice varieties, as measured by texture profile analysis, were investigated. Instrumentally measured textural properties were not significantly (α = 0.05) affected by drying conditions, with the exception of cohesiveness. Cohesiveness was lower in rice dried at lower temperatures (18°C or ambient) than in that dried at the higher commercial temperatures. Final moisture content and degree of milling significantly (α = 0.05) affected textural property values for adhesiveness, cohesiveness, hardness, and springiness; their effects were interdependent. The effects of deep milling were more pronounced in the rice dried to 15% moisture than that dried to 12%. In general, textural property values for hardness were higher and those for cohesiveness, adhesiveness, and springiness were lower in regular-milled rice dried to 15% moisture than in that dried to 12%. In contrast, hardness values were lower and cohesiveness, adhesiveness, and springiness values were higher in deep-milled rice dried to 15% moisture than in that dried to 12% moisture. Deep milling resulted in rice with lower hardness values and higher cohesiveness, adhesiveness, and springiness values.     

Compression Deformation and Structural Relationships of Medium Grain Cooked Rice

Cooked rice quality is based on a number of factors including texture. Texture and structure of foods are closely related and aspects of the relationship can be explored by correlating compression measurements to structural observations of the compressed material. To obtain compression measurements, single cooked, milled rice grains were compressed in a texture analyzer to a specific percentage (% compression) of the original grain; the uncompressed grain is 0%. The experiment, using single grains in each case, was repeated multiple times. Compression percentages of 20, 30, 40, 50, 60, and 70% were measured against a constant resistance force in the texture analyzer. Structures of cooked rice grains at the various compression levels were compared by brightfield and fluorescence microscopy. The outside of an uncompressed, intact, cooked rice grain is swollen and distorted while the interior has three or more odd‐shaped holes (voids). Each void is largest in the center of the grain and decreases in size toward the peripheral edges becoming fine cracks toward the outermost portion of the void. The voids tended to increase in area up to 40% compression and then decrease in area upon further compression. Percent compression versus resistance force was a curvilinear relationship. With increasing % compression, cell shapes became increasingly more rounded, although there wasn't much effect on the integrity of cell walls with increasing % compression. The degree to which grain structure changed during the various compression tests, combined with the curvilinear behavior of resistance force versus % compression, indicates that the voids and cell walls have an effect on texture.     

Site of Origin of Volatile Compounds in Cooked Rice

Volatile compounds emanating from three cultivars of cooked rice milled to different degrees (0, 8, and 30% by weight) were compared to ascertain their site of origin and the effect of pigmentation on synthesis. The cultivars tested were Ilpumbyeo (traditional white rice), Heugjinjubyeo (black pigmented), and Jeogjinjubyeo (red pigmented). In total, 29, 38, and 27 volatile compounds were identified in dehulled, unmilled Ilpumbyeo, Heugjinjubyeo, and Jeogjinjubyeo, respectively. Significant quantitative and qualitative differences were found among the cultivars in their volatile profiles. 2‐Acetyl‐1‐pyrroline, guaiacol, 1‐nonanol, 3‐octen‐2‐one, 1,2‐dimethoxybenzene, pyridine, and pyrrole were found only in Heugjinjubyeo and phenylacetaldehyde only in Jeogjinjubyeo. Removal of the bran, partial endosperm, and pigment qualitatively and quantitatively affected the volatile compounds formed, with certain volatiles higher in unmilled rice (0% milling), indicating the pericarp and aleurone layer (bran) as their primary site of origin. Volatiles emanating from the 8 and 30% milled samples indicated the outer and middle endosperm (8%) and core endosperm (30%) as the primary sites of origin. Therefore, differences in chemical composition with location within the grain appear to account for the quantitative and qualitative variation in volatile synthesis.