Rice bran protein isolate (RBPI) containing approximately 92.0% protein was prepared from unstabilized and defatted rice bran using phytase and xylanase. The yield of RBPI increased from 34% to 74.6% through the use of the enzymatic treatment. Nitrogen solubilities of RBPI were 53, 8, 62, 78, 82, and 80% at pHs 2.0, 4.0, 6.0, 8.0, 10.0, and 12.0, respectively. Differential scanning calorimetry showed that RBPI had denaturation temperature of 83.4 degrees C with low endotherm (0.96 J/g of protein). RBPI had similar foaming properties in comparison to egg white. But emulsifying properties of RBPI were significantly lower than those of bovine serum albumin. The result of amino acid analysis showed that RBPI had a similar profile of essential amino acid requirements for 2-5-year-old children in comparison to that of casein and soy protein isolate.

A true understanding of rice kernel fissuring and breakage, as a result of drying and tempering, must include both engineering and cereal science principles. Particular emphasis must be placed on the change of states of starch occurring at the glass transition temperature (T g). This transition from a glassy to rubbery state, or vice versa, has been identified to play an important role in rice fissuring and breakage. A hypothesis has been developed explaining rice kernel fissuring during drying and tempering. The objectives of this research were to determine the effect of the T g during rice drying and tempering on milling quality. Additionally, the minimum tempering time required for various drying conditions, to optimize milling quality, was determined. Rice was dried under three conditions, two with a drying air temperature above T g and one below T g , for four durations and then tempered for 0 to 240 min. The experimental procedure was designed to directly test the T g hypothesis by cooling rice to a temperature below the T g after each tempering duration. Results for both medium-grain rice and long-grain rice at 19.6 to 23.7% harvest moisture content (MC) * show that 5 to 6 percentage points MC can be removed per drying pass without damaging the rice kernel, as long as sufficient tempering is allowed. Required tempering durations were shorter for long-grain rice as compared to medium-grain.

Future increases in global surface temperature threaten those worldwide who depend on rice production for their livelihoods and food security. Past analyses of high-temperature stress on rice production have focused on paddy yield and have failed to account for the detrimental impact of high temperatures on milling quality outcomes, which ultimately determine edible (marketable) rice yield and market value. Using genotype specific rice yield and milling quality data on six common rice varieties from Arkansas, USA, combined with on-site, half-hourly and daily temperature observations, we show a nonlinear effect of high-temperature stress exposure on yield and milling quality. A 1°C increase in average growing season temperature reduces paddy yield by 6.2%, total milled rice yield by 7.1% to 8.0%, head rice yield by 9.0% to 13.8%, and total milling revenue by 8.1% to 11.0%, across genotypes. Our results indicate that failure to account for changes in milling quality leads to understatement of the impacts of high temperatures on rice production outcomes. These dramatic losses result from reduced paddy yield and increased percentages of chalky and broken kernels, which together decrease the quantity and market value of milled rice. Recently published estimates show paddy yield reductions of up to 10% across the major rice-producing regions of South and Southeast Asia due to rising temperatures. The results of our study suggest that the often-cited 10% figure underestimates the economic implications of climate change for rice producers, thus potentially threatening future food security for global rice producers and consumers.

Cereal Chem. 85(3):276-282Rice quality can vary inexplicably from one lot to another and from year to year. One cause could be the variable temperatures experienced during the nighttime hours of rice kernel development. During the fall of 2004, a controlled temperature study was conducted using large growth chambers, testing nighttime temperatures of 18, 22, 26, and 30°C from 12 a.m. until 5 a.m. throughout kernel development, using rice cultivars Cypress, LaGrue, XP710, XL8, M204, and Bengal. As nighttime temperature increased, head rice yields (HRY) significantly decreased for all cultivars except Cypress and Bengal, for which HRY did not vary among nighttime temperature treatments. Kernel mass did not vary among temperature treatments for any cultivar. Grain dimensions generally decreased as nighttime temperature increased. The number of chalky kernels increased with an increase in nighttime temperature for all cultivars but Cypress. The amylose content of Cypress and LaGrue was significantly lower at the nighttime temperature of 30°C, while total brown rice lipid and protein contents did not vary among temperature treatments for all cultivars.Rice is primarily consumed as an intact kernel and therefore production quality is largely measured by head rice yields (HRY), which is the mass percentage of rough rice kernels that remain as head rice (kernels that are ≥75% of a whole, milled kernel (USDA 2005). Broken rice is worth only 50-60% of the value of head rice, meaning that a reduction in HRY can have severe economic repercussions for rice producers. Therefore, maximizing HRY is a major concern. Producers can influence HRY by optimally choosing harvest dates to avoid kernel fissure formation due to rapid moisture adsorption in the field (Kunze 1977). Improper drying and storage procedures can also cause kernel fissuring that can reduce HRY (Daniels et al 1998).While HRY is determined in part by production practices, HRY can vary inexplicably from year to year and often from field to field, making it difficult for producers to predict yearly income and for processors to maintain a consistent end product. Moreover, in a given year, HRY can be uniform in one cultivar of rice and yet variable in another cultivar, leading to the suspicion that some cultivars are more resistant to quality variation. To achieve uniformity in the quality characteristics of rice, it is first necessary to have a clear understanding of the causes of these quality variations.Rice quality can be influenced by genetics and environmental conditions such as ambient temperature during rice plant development (Webb et al 1979). While rice genetics can be altered through breeding programs, environmental temperatures are difficult to predict and can only be manipulated to some extent with the choice of planting dates. Environmental temperature during kernel development may play an integral role in causing the observed, unexplained fluctuations in rice grain quality (Cooper et al 2006).Historical analyses have indicated that decreased yields were ...

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Cereal Chem. 82(6):645-648Important rice grain quality characteristics such as percentage of chalky rice kernels are affected by both high and low night temperatures and by different day and day/night temperature combinations. High nighttime temperatures have also been suspected of reducing rice milling quality including head rice yields. Experiments to confirm or refute this have not been reported. A controlled climate experiment was conducted. Conditions in the chambers were identical except between 2400 and 0500 hours (midnight and 5 am). For those times, two temperature treatments were imposed: 1) 18°C (low temperature treatment) and 2) 24°C (high temperature treatment). Two cultivars were tested: LaGrue and Cypress. The high temperature treatment reduced head rice yields compared with the low temperature treatment. Grain widths were reduced for the high temperature treatment compared with the low temperature treatment. There was no effect of temperature on grain length or thickness. Amylopectin chain lengths 13-24 were increased by the high temperature treatment by ≈1%. Future research will focus on determining whether genetic variability exists among cultivars in their head rice yield response to high temperatures. After identifying a source of resistance to high temperature effects, this characteristic can be incorporated into rice cultivars. In addition, ways to reduce this effect, including biotechnological remedies, have the potential for increasing rice yield and quality.

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The effect of moisture content (MC) on the glass transition temperature (Tg) of individual brown rice kernels of Bengal, a medium‐grain cultivar, and Cypress, a long‐grain cultivar, was studied. Three methods were investigated for measuring Tg: differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and dynamic mechanical analysis (DMA). Among these methods, TMA was chosen, because it can also measure changes in the thermal volumetric coefficient (β) of the kernel during glass transition. TMA‐measured Tg at similar MC levels for both cultivars were not significantly different and were combined to generate a brown rice state diagram. Individual kernel Tg for both cultivars increased from 22 to 58°C as MC decreased from 27 to 3% wb. Linear and sigmoid models were derived to relate Tg to MC. The linear model was sufficient to describe the property changes in the MC range encountered during rice drying. Mean β values across both cultivars in the rubbery state was 4.62 × 10‐4/°C and was higher than the mean β value of 0.87 × 10‐4/°C in the glassy state. A hypothetical rice drying process was mapped onto the combined state diagram generated for Bengal and Cypress.