Rough Rice Grains Research Articles

A NATURAL CONVECTION SOLAR DRYER FOR ROUGH RICE

A solar drying system was constructed and tested to dry rough rice grains for seeding under Zagazig city prevailing weather conditions. The system consists of two integrated units, a solar collector with total area of 1.8 m2 attached to a drying chamber. The system is classified as a natural convection indirect passive cabinet type without any moving parts. The study parameters included varying the air inlet area from 244 to 732 cm2, testing three levels of initial moisture contents (20, 22, and 25% w.b.), and two different grain layer thicknesses of 5 and 10 cm. The system was operated from 8 AM to 5 PM under Zagazig local conditions (Latitude 30.5° N) for 2 weeks during the rice harvesting season of 2009. The results showed that the smallest air inlet area of 244 cm2 gave the highest collector thermal efficiency, the highest temperature difference between ambient air and heated air inside the collector, and highest drying rate. Also the initial moisture content of 20% w.b. gave the highest drying rate and fastest drying time. Same results were found using layer thickness of 5 cm. So the combination of 244 cm2 air inlet area, 5 cm layer thickness, and 20% initial moisture content is recommended for the best thermal performance and highest drying rate.

Tillage, Seeding, and Nitrogen Rate Effects on Rice Density, Yield, and Yield Components of Two Rice Cultivars

Research was conducted for 2 yr on a Crowley silt loam soil (fine, smectitic, thermic Typic Albaqualfs) near Crowley, LA to evaluate the main effects of tillage, seeding and N rate and potential interactions on rice (Oryza sativa L.) density, yield, and yield components. Two tillage systems (conventional and fall‐stale seedbed), four seeding rates (162, 323, 484, and 646 seed m−2) and four N rates (101, 134, 168, and 202 kg ha−1) were evaluated. ‘Jupiter’ and ‘Cheniere’ a medium and long grain cultivar, respectively, were evaluated in separate experiments. Conventional tillage reduced rice plant density as compared with fall‐stale seedbed tillage due to crusting following flush irrigation during seedling emergence. A tillage by N rate interaction was not observed, suggesting optimal N rates are similar for rice grown using a conventional or fall‐stale seedbed. Rough rice grain yield was optimized at 202 and 168 kg N ha−1 for Jupiter and Cheniere, respectively. Grain yields were optimized for Jupiter at 323 seed m−2, while Cheniere required a seeding rate of more than 323 seed m−2 Panicle density was found to be the single most influential yield component on rice yield and was able to explain 49 and 51% of the variation in yield for Jupiter and Cheniere, respectively. Filled grain panicle−1 was inversely related to panicle density highlighting the ability of rice to tiller as a yield compensatory measure when less than optimum rice densities exist. However, total yield compensation may not be feasible at low seeding rates.

Physical Properties of Rough Rice

Knowledge of the physical and mechanical properties of the rice grain is being used in the handling, planting, harvesting, threshing, cleaning, size grading, up grading, treating and packaging. Several physical properties of three rough rice cultivars (Poya, Khazar and Haraz) were determined and compared in terms of length, width, thickness, aspect ratio, arithmetic diameter, geometric diameter, equivalent diameter, sphericity, mass, volume, surface area, bulk density, true density and porosity. A linear model for describing the mass of rough rice grain for each cultivar was also investigated.

GABA Enriching Characteristics of Rough Rice Grain

GABA Enriching Characteristics of Rough Rice Grain

Finite Element Simulation of Rough Rice Kernel (Oryza sativa L.) cv. Fajer Drying

This study was conducted to present a mathematical model with numerical solutions to predict the mass distributions inside a cross sectional area of an individual Fajer variety of rough rice (Oryza Sativa L.) kernel as a function of drying time considering the effects of coupled heat and mass transfer processes. The modified Luikov's equation was used for the simulation of drying kinetics of a single rough rice grain. The applied drying models with simultaneous heat and mass diffusion in biological materials were developed by finite element method. A finite element formulation and solution of a set of nonlinear coupled conductive heat and diffusive moisture transfer equation to improve grain drying simulation of axisymmetric bodies is presented. Axisymmetric linear triangular elements with two degrees of freedom per node were used to discretize the rice grain. Moisture distribution inside the individual rough rice kernel was produced by the model. Good agreement was observed when the output of nonlinear model was compared to experimental data.

Compressive Load Resistance Characteristics of Rice Grain

Investigation was made to observe the compressive load property of rice gain both rough rice and brown grain. Six rice varieties (indica and japonica) were examined with the moisture content at 10-12%. Compressive loads with reference to a principal axis normal to the thickness of the grain were conducted at selected inclined angles of 0°, 15°, 30°, 45°, 60° and 70°. The result showed the compressive load resistance of rice grain based on its characteristic of yield strength, of which can be expressed as relationships of the shear strength. Two similar experiments, both parallel and cross grain positions were conducted on the rough rice and brown rice. Result showed the trend of load resistance of rice grain, which may be used as an important parameter for the design of related post-harvest machines. The properly designed machine in conjunction with this compressive strength might lead to the minimal use of power consumption of the machines as well as lowering the broken rice during the rice mill processes.

A diffusion based model for intermittent drying of rough rice

In this study, intermittent drying behavior of single layer rough rice with a moisture content of between 22 and 24% on the dry basis was simulated by means of a liquid diffusion model based on a prolate spheroid geometry. For this purpose, solution of the liquid diffusion equation was fitted to the experimental data for the drying air temperature 40°C, drying velocity 1.5 ms−1 and tempering periods ranging from 0 to 1 h. In order to make a comparison, solution of the liquid diffusion equation for a finite cylindrical geometry was also fitted to the experimental data. The results show that the liquid diffusion model based on a prolate spheroid geometry explains the drying behavior of rough rice more accurately. The results also show that greater variations occur in diffusion coefficient with increasing tempering time for prolate spheroid geometry which is more realistic geometry for a rough rice grain.

Some physical properties of rough rice ( Oryza Sativa L.) grain

Designing the equipment for processing, sorting, sizing and other post-harvesting equipment of agricultural products requires information about their physical properties. In this study, various physical properties of rough rice cultivars were determined at a moisture content of 10% (wet basis). In the case of Sorkheh cultivar, the average thousand grain weight, equivalent diameter, surface area, volume, sphericity, aspect ratio, true density, bulk density and porosity were 21.64 g, 3.35 mm, 31.76 mm 2, 20.27 mm 3, 39.71%, 0.28, 1269.1 kg/m 3, 544.34 kg/m 3, and 56.98%, respectively. The corresponding values were 20.52 g, 3.4 mm, 32.58 mm 2, 21.06 mm 3, 39.88%, 0.29, 1193.38 kg/m 3, 471.21 kg/m 3, and 60.37% for Sazandegi cultivar. For Sorkheh cultivar, the average static coefficient of friction varied from 0.2899 on glass to 0.4349 on plywood, while for Sazandegi cultivar the corresponding value varied from 0.2186 to 0.4279 on the same surfaces. Angle of repose values for Sorkheh and Sazandegi cultivars were 37.66° and 35.83°, respectively. Linear model for describing the mass of rough rice grain was investigated. Mass was estimated with single variable of kernel length with a determination coefficient as 0.862 for Sorkheh cultivar whereas for Sazandegi cultivar was as 0.860.

Water absorption and starch gelatinization in whole rice grain during soaking

Hydration of rough rice grain in hot water as a function of time was studied at temperature range 25–90 °C. A simple model which considers simultaneous unsteady-state water diffusion and first-order irreversible water–starch reaction phenomenon, was used to evaluate the kinetics parameters from experimental curves. The values of the diffusion coefficients and reaction rate constants were between 1.40×10 −11 and 9.36×10 −11 m 2 s −1 and 2.29×10 −10 and 3.72×10 −5 s −1, respectively. Both parameters followed a Arrhenius-type equation with distinct activation energies below and above a break temperature of 60 °C. It was 25.4 and 289.3 kJ mol −1 for the activation energies of diffusion and reaction, respectively, below 60 °C. Above this temperature the respective values of the activation energies of diffusion and reaction were 30.0 and 16.6 kJ mol −1. This break temperature was in agreement with the gelatinization temperature determined experimentally.

Seeding Rates for Stale Seedbed Rice Production in the Midsouthern United States

The establishment of an adequate and uniform rice (Oryza sativa L.) stand is critical to achieve high grain yields. The literature is extensive for older cultivars planted in conventional tillage and/or water‐seeded systems; however, there are no published data for current cultivars grown in stale seedbed systems. Six of the cultivars most commonly grown in the Midsouth rice production area of the USA were drill seeded at densities of 108, 215, 323, 430, and 538 seeds m−2 into a stale seedbed at Crowley, LA, from 2002 to 2004, and in Clarksdale, MS, in 2003 and 2004. Established plant densities responded linearly to seeding rate for all cultivars except Cocodrie, which responded quadratically. Rough rice yields were not affected by seeding rate for Cheniere, but followed a quadratic relationship for the cultivars CL161, Cocodrie, and Priscilla. A location × seeding rate interaction was detected for yield of Wells. Seeding rate did not affect rough rice yields for Wells in Mississippi, while in Louisiana, yields responded quadratically. Francis rough rice yields increased linearly with increased seeding rates. Optimal rough rice grain yields can be achieved in Mississippi and Louisiana with a seeding rate of 323 seeds m−2 for cultivars that are currently grown across the Midsouth rice‐producing area in the USA. Furthermore, depending on the cultivar, when plant densities are uniform and range from 50 to 70 plants m−2, the resulting rice grain yields may offset the cost of terminating the stand and replanting.

Rice Response to Planting Date Differs at Two Locations in Louisiana

Planting date can have a dramatic effect on crop development and yield. Determining if rice cultivars respond differently to planting date is important when selecting the most appropriate cultivar for a particular planting date. Research was conducted from 1995 through 1997 at two locations in Louisiana to determine the number of days from seedling emergence to 50% panicle emergence and rough rice grain yield of the cultivars Bengal, Cypress, Jodon, and Kaybonnet when drill seeded at five dates ranging from late March through early June. The interaction of cultivar by planting date for days required to reach 50% panicle emergence and rough rice grain yield was not significant. However, planting date had a major effect on days required to reach 50% panicle emergence and grain yield. Grain yield at one location in southwest Louisiana was highest (8600 kg/ha) when rice was planted in late March, and grain yield decreased linearly as planting was delayed until early June (6500 kg/ha). In northeast Louisiana, grain yield was lower when seeded in late March (5200 kg/ha), increased to a maximum in mid-April (7200 kg/ha), and decreased throughout the latter planting dates. Days from seedling emergence to 50% panicle emergence decreased at both locations as planting was delayed.

Freezing Temperature and Freezing Injury of Rough Rice Grains with Various Levels of Moisture Content

Freezing Temperature and Freezing Injury of Rough Rice Grains with Various Levels of Moisture Content

Liquid diffusion model for intermittent drying of rough rice

Intermittent drying of rough rice grains forming a thin layer was experimentally investigated. An analytical solution of the liquid diffusion equation based on a finite circular cylinder geometry for the rice grain was fitted to the experimental data. The effect of the tempering on the drying rate of rough rice grains was reflected as an increase in the effective diffusion coefficient. The drying rate of the rough rice grains was found to increase with longer tempering periods.

MODELLING ADSORPTION EQUILIBRIUM MOISTURE CHARACTERISTICS OF ROUGH RICE

Equilibrium Moisture Content (EMC) data for medium rough rice grain, Lido variety were obtained by equilibrating rice samples at different Equilibrium Relative Humidities (ERH) and Temperatures. The employed models to fit the data were GAB, modified Chung-Pfost, modified Halsey, Modified Henderson, and modified Oswin. The data were evaluated using the standard error of moisture content, mean relative standard error (%P) of the model and the correlation coefficient r2. The GAB model by indirect regression described the EMC the best, however its parameters lacked of physical meaning. The modified Chung-Pfost and modified Henderson equations presented a similar fit of the EMCERH relationships. The modified Chung-Pfost equation had lower residual values than the modified Henderson equation and was considered the best model to explain the EMC-ERH relationships.

The Relation between Number of Rough Rice Grains and the Quality of Brown Rice during the Ripening of Rice

The Relation between Number of Rough Rice Grains and the Quality of Brown Rice during the Ripening of Rice

Transient Moisture Gradients in Rough Rice Mapped with Finite Element Model and Related to Fissures After Heated Air Drying

A two-dimensional diffusion equation was solved by the finite element method to estimate transient moisture gradients in the endosperm of a rice grain. Moisture elevated samples of 150 rough rice grains were dried for different durations with different air temperatures. Fissured grains were counted immediately after drying and at periodic intervals of 12 h. High initial moisture contents and high drying air temperatures caused the most fissured grains. Transient moisture gradients at several locations of the rice endosperm are presented at selected periods during and after drying. The relationships between the transient moisture gradients and the resulting fissured grains are explained.

Impact Damage on Rough Rice

‘Lemont’ and ‘Rico’ rice were harvested at 17-19% moisture content and then dried to 10.7-11.5% for storage. Impact damage on rough rice was evaluated as a function of variety, cylinder peripheral speed, grain moisture, and number of passes through the thresher. Grains broke more rapidly at higher than at lower moisture levels. Dehusking of the grain increased with an increase in cylinder peripheral speed and the number of passes through the thresher. The highest percentage of unfissured brown rice was obtained at the lower moisture levels. At the intermediate speeds, fissured rough rice grains generally contributed more to breakage than the unfissured rough rice. Some impacts are sufficient to fissure a good grain without rupturing its hull to give brown rice.

Biological Half-life of Gaseous Elemental Iodine Deposited Onto Rice Grains

In order to obtain the biological half-life (Tb) of iodine deposited on rough rice grains, rice plants of four different growing stages--heading, milky, dough, and yellow ripe--were exposed to elemental gaseous iodine. After the exposure, the rough rice samples were collected at different intervals and analyzed for iodine to estimate the value of Tb. The average value of Tb obtained by the experiments at the dough and yellow ripe stages was about 200 d. This value is considerably larger than those for pasture grass and leafy vegetables.

The temperature dependence of isosteric heat of sorption of some cereal grains

SummaryAn equation predicting the temperature dependence of the isosteric heat of sorption was calculated using the Othmer method. This equation was applied to water vapour pressure isotherms of cereal grains (sorghum, wheat and rough rice) at different temperatures to calculate the isosteric heat and its dependence on moisture content and temperature. The results show a slight decrease of the isosteric heat with increasing temperature. For rough rice grain, the desorption heats calculated by the proposed method at two temperatures were compared with those obtained by the Clausius‐Clapeyron method.

Moisture desorption isotherms of rough rice

SummaryDesorptions isotherms of rough rice have been determined at 40, SO, 60 and 70°C and water activities (a,) from 0.036 to 0.823. An attempt is made to describe the experimental equilibrium moisture content data using mathematical relationships available in the literature. A statistical analysis was performed to evaluate the goodness of fit of the different equations. From this analysis it was concluded that Henderson's equation permits to correlate satisfactorily the experimental data for the whole range of water activity investigated. Finally, a simple empirical equation was postulated to take into account the effect of temperature on water sorption isotherms of rough rice grain.