Current Research Projects

Preharvest Property Characterization
Drying
Milling
On-farm Rice Drying, Storage and Safety
Alternative Treatments for Rice Drying and Pest Control
Starch Chemistry

Sensory Analysis


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Preharvest Property Characterization

Faculty Member: Dr. Terry Siebenmorgen

1. Quality of rice produced using alternative flooding practices.
The availability of water is a critical issue to the long-term sustainability of rice production. The impacts of alternative irrigation practices are being quantified in production-level fields through a collaborative project with Dr. Michele Reba of the USDA. The RPP is quantifying milling yield impacts of irrigation and land-leveling practices.

2. Fissure formation rates due to moisture adsorption using an x-ray system.
Rapid moisture adsorption by low-moisture content (MC) rice in fields remains a major cause of milling yield reductions and economic loss to producers. A project is being conducted to quantify fissure counts by various means, including x-ray imaging, and to relate the fissure counts to milling yield levels. This work is intended to not only help illustrate this phenomenon to producers, but also to provide information to instrument developers who are seeking rapid means of predicting milling yields.

Faculty Member: Dr. Paul Counce

3. Relation of rice panicle architecture to yield quality.
Rice yield and quality are both related to the number of grains per panicle. There is usually a direct positive relationship between yield and number of grains per panicle. And there is often a direct negative relationship between yield and number of grains per panicle. In high yield situations which are a requirement for U.S. rice production, we have achieved these yields by steadily increasing the number of grains per panicle while simultaneously decreasing the total duration of the rice growing season. This work is intended to allow us to understand these relationships better and adjust both processing and breeding practices to improve quality while simultaneously increasing grain yields.

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Drying

Faculty Member: Dr. Terry Siebenmorgen

1. Effects of airflow rates on temperature and MC profiles in cross-flow driers.
Cross-flow driers are by far the most popular means of drying rice in the Mid-South. A drying apparatus/technique was constructed to allow measurement of rice temperature and MC throughout a drying column during drying under a range of conditions, including a range of airflow rates. The data will be used for several applications, including validating a mathematical simulation of cross-flow drier operation.

2. Impacts of airflow in cross-flow driers on energy efficiency and throughput.
Little to no data exists that indicates the optimal airflow rate to use in cross-flow driers. The experimental data described above will be used to quantify the effect of airflow rate on energy-use efficiency and water removal rates/rice MC reduction in cross-flow driers. This quantification will be used in a larger effort of optimizing airflow rates in these driers.

3. Impacts of tempering approaches on rice kernel fissuring.
Previous drying research has shown the importance of post-drying tempering on milling yields. Trials have been conducted using the experimental apparatus above to evaluate milling yield reductions associated with various tempering approaches. The data will yield information on best practices to
handle rice immediately exiting driers.

4. Application of Tg principles to explain fissuring during cross-flow drying.
Experimental work has investigated the impact of glass transition temperatures (Tg) and material state gradients to explain fissure development during drying, but practically all of this has been done using thin layers of rice. The impact of such gradients is being quantified in bulk, column drying using the experimental data above. It is hoped that this work will reveal when and why fissures develop during drying in cross-flow driers.

5. Mathematical modeling of cross-flow drier operation.
There are many variables that must be considered when optimizing the performance of cross-flow driers for drying rice; mathematical models enable this. A model has been developed that predicts air and rough rice MC and temperature profiles throughout the column of a cross-flow drier. The model is now being refined using experimentally-determined drying rates, described below, and validated using data from the laboratory drying apparatus described above. The model will be used to evaluate many variables in order to provide recommendations for cross-flow drier operation and potential design modifications.

6. Drying rates of thickness-graded kernels in thin layers.

Our recent work has shown that there can be a significant difference in drying rates of kernels with different thicknesses. Drying curves of thickness-fractionated kernels are being conducted to provide better estimates of bulk drying rates. This work will improve the prediction of drying rates, and thus the accuracy, of the mathematical model above.

7. Relative impact of kernel thickness and MC in determining kernel fissuring.
Milling yield reductions during the drying process would be understood more thoroughly if the impact of kernel thickness and MC were fully quantified. A recently-acquired x-ray system, retrofitted with a specially-designed drying system, is being used to elucidate these relative impacts; the study is being conducted in coordination with the drying work on thickness-graded rice above. The results are intended to further refine the Tg hypothesis and provide recommendations for optimizing the rice drying process.

8. Quality kinetics of rice stored under various conditions prior to drying.
The recent adoption of energy-saving, sensor-based drying strategies in farm drying and storage bins has, in certain scenarios, allowed rice in the upper layers of bins to remain at elevated MCs and temperatures for extended durations. An experiment is nearing completion in which rough rice was stored over a wide range of rice MCs and temperatures; milling quality and functionality were monitored over storage duration. This research will provide recommendations to rice producers in terms of the storage-condition limits above which quality, particularly discoloration, will degrade.

9. Impacts of storing cooled, high-MC rice on parboiling performance.
It has been proposed that freshly-harvested rice be cooled using grain coolers, which would allow temporary storage at high MC. The possibility of using this cooled, high-MC rice for parboiling, thereby avoiding drying the rice, is being investigated by storing rough rice at temperatures that could be achieved through cooling. The results are anticipated to provide data that can be used to evaluate the feasibility of this approach.

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Milling

Faculty Member: Dr. Terry Siebenmorgen

1. Impacts of rough rice thickness grading prior to milling on milling yields.
Previous work has shown the impact that rice kernel thickness has on milling yields. Studies were conducted to thickness grade rough rice, measure properties of each fraction, and then mill each fraction separately. The thinner-kernel fractions showed much reduced milled rice yields and head rice yields, and generally had increased chalkiness. The results are intended to provide data for evaluating the commercial application of thickness grading.

2. Physical and functional characteristics of rice kernel brokens produced by moisture adsorption.
Rapid moisture adsorption of dried rice kernels prior to harvest is one of the most prevalent ways that kernels fissure and subsequently break apart to create brokens during milling. Many of these brokens are used for rice flour. Brokens were created by drying rough rice to various levels and then soaking the kernels to induce fissuring. The physical properties of the resulting brokens, as well as the functional properties of flour from the brokens, were assessed. This project provides basic information on rice flour and how the physical properties of brokens impact flour functionality.

3. Physical and functional characteristics of brokens from rice lots with varying chalkiness and harvest MC.
As the demand for rice flour is increasing, it is important to know how and why flour functional characteristics vary. A study in underway to quantify functional characteristics of flour from brokens that were produced in various ways, including moisture adsorption fissuring, breakage of immature kernels from high-MC lots, and breakage due to chalkiness. This data is intended to provide at least partial explanations to processors as to functional variability in rice flour.

4. Evaluation of the safe moisture content that rough rice can be stored over time.
Rough rice in the United States is typically dried to approximately 12.5% MC (w.b.) for long-term storage and subsequent milling. However, if rice could be stored at greater MCs, drying costs could be significantly reduced. A project was initiated this fall to store three rough rice lots of varying quality over a range of MCs to determine the kinetics of milling performance, milled rice color, and microbial growth. The project will provide insight as to whether rough rice can be stored at MCs greater than 12.5% without quality ramifications.

5. Quantifying the millability of a wide range of rice cultivars.
Milling performance and functionality of rice can vary tremendously from year-to-year, but also from cultivar-to-cultivar. In collaboration with RiceTec, a study was initiated this fall to collect samples from 13 hybrid and pureline cultivars grown side-by-side in commercial plots located in Northeast Arkansas. A complete analysis of physical and functional properties, as well as milling performance, will be conducted. The data is intended to characterize data for millers and processors for the common cultivars grown in Arkansas.

6. Iron fortification of rice using parboiling (in collaboration with Dr. Ya-Jane Wang).
People in many areas of the world suffer from iron deficiency, but in many of these same areas, rice is a staple food and it is often parboiled for consumption. A project is being conducted to investigate the penetration rates of iron into the kernel endosperm by using various rice feedstock and parboiling conditions. The project results are intended to provide a more effective means of fortifying food aid rice, as well as rice prepared locally in areas in which iron is deficient in diets.

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On-farm Rice Drying, Storage and Safety

Faculty Member: Dr. Griffiths Atungulu

1. Refining equilibrium MC isotherms of rice for accurate modeling of in-bin drying and storage scenarios.

2. In-bin rice drying and storage simulation, validation and assessment of operations using new cabling technology.

3. In-bin rice chilling aeration simulation, validation and economic evaluation for Arkansas conditions.

4. Impact of low-temperature/natural air rice drying and storage environments on mycotoxin formation.

5. Microbial prevalence on rice and role on rice discoloration and other quality attributes.

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Alternative Treatments for Rice Drying and Pest Control

Faculty Member: Dr. Griffiths Atungulu

1. Selectivity of infrared wavebands to inactivate toxigenic fungi– Aspergillus flavus.

2. Development of one-pass drying of rice using microwave heating.

3. Quality kinetics of rice dried using microwaves and infrared treatments.

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Starch Chemistry

Faculty Member: Dr. Ya-Jane Wang

1. Starch structure and rice quality.
Breeding activities aimed at improving and broadening rice germplasm have resulted in differences in the cooking, eating, and processing characteristics among rice cultivars. Therefore, rice quality become less predictable solely based on amylose content because of diversification of rice varieties. The goal of this research is to determine starch structure and functionality relationship and develop/establish alternative more reliable predicators and/or techniques that could adequately explain the complexities in rice functionality.

2. Applying starch polymorphism to optimize product and process development of rice.
Parboiling involves soaking, steaming and drying to improve head rice yield, prolong shelf-life, and maintain greater nutrients of rice. The soaking step alone in parboiling has been shown to remove fissures and chalkiness and improve the strength of rice kernels. It is proposed that the percentage of intact kernels of non-parboiled rice can be improved by allowing mobility and rearrangement of starch molecules in rice kernels during soaking, which will result in increased crystallinity and reduced structural defects, and also dramatically reduce energy use and increase processing throughput. The work is to determine the roles of amylose and amylopectin structures on the formation and removal of structural defects, and to relate starch polymorph changes due to various soaking conditions to rice properties in non-parboiled rice.

3. Effects of soaking conditions on parboiled rice properties.
The soaking step in parboiling has been traditionally done under excess water, which presents opportunity in conserving water and energy. This work is to explore the possibility of using limited water soaking while still achieving similar milling, physicochemical, and cooking qualities of parboiled rice.

4. Effects of kernel thickness on parboiled rice properties.
The thickness of individual kernels at harvest varies widely and may impact parboiled rice properties. This work investigated the impact of kernel thickness on milling and physicochemical properties of rice cultivars after parboiling.

5. Amylolytic activities in germinated brown rice of varying amylose contents under aerobic and anaerobic conditions.
Germination is a biomodification process that activates enzymatic activities, such as a-amylase, protease and lipase in the bran layer, which degrade starch, protein and lipid, respectively. Germinated brown rice is primarily known for its significant gamma-aminobutyric acid (GABA) content. Moreover, the development of amylolytic activities presents novel applications for in situ modification of starch without the addition of external enzymes. This work will investigate the amylolytic activities of germinated brown rice from long-grain, medium-grain, short-grain and waxy rice cultivars under aerobic and anaerobic conditions for different germination times.

6. Applications of germinated rice in product development.
The hydrolysis pattern of starch with varying amylose contents by germinated rice from different germination conditions will be investigated to develop products with novel properties.

7. Rice fortification through parboiling.
Rice is a valuable vehicle for nutrition improvement through micronutrient fortification. The success of rice micronutrient fortification has remained a technological challenge. This work will investigate the effect of parboiling conditions on fortification of rice with micronutrients.

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Sensory Analysis

Faculty Member: Dr. Han-Seok Seo

1. Impacts of thickness-graded kernels on sensory characteristics of uncooked and cooked rice.

2. Effects of cultivating location on sensory characteristics of cooked rice.

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