Physical and Water Absorption Characteristics of Some Improved Rice Varieties

Abstract

The physical and water absorption characteristics of paddy and brown rice from some early maturing Oryza sativa varieties and newly developed interspecific (O. sativa × Oryza glaberrima) rice varieties were studied. The physical dimensions (length, breadth and width, length/ width ratio, equivalent diameter), grain surface area and volume, sphericity, 1,000-kernel weight, bulk and true densities as well as porosity were determined. A nonlinear moisture diffusion equation was used to model the water absorption curves of the rice varieties at 30-60°C. Digital images of the rice grains were analyzed for their tristimulus color parameters (L*, a*, b*). The physical characteristics of the rice varieties differed significantly (p<0.05). The rice grains were of medium size with length/width ratio ranging between 2.80 and 3.50. Notably, the New Rice for Africa variety WAB 450 aka NERICA 1 had the smallest 1,000-kernel weight and the highest husk/paddy weight ratio. The equilibrium moisture content was significantly influenced (p<0.01) by the soaking temperature and the rice component being soaked. The hydration rate curves were generally characterized by two falling rate periods. The predicted water absorption curves were very close to experimental curves (0.91<r 2 <1.00, p<0.01). The interspecific variety (NERICA 1) had higher effective moisture diffusivity compared to the early maturing O. sativa varieties. Keywords Rice . NERICA . Physical properties . Hydration . Paddy . Brown rice . Modeling Nomenclature Φ Sphericity (percent) L Length (millimeters) W Width (millimeters) T Thickness (millimeters) ρ b Bulk density (kilograms per cubic meter) ρ s Solid density (kilograms per cubic meter) ε Porosity (percent) V Grain volume (cubic millimeters) S Surface area of grain (square millimeters) D e Equivalent diameter (millimeters) L* Lightness a* Redness b* Yellowness MR Moisture ratio M Instantaneous moisture content (percent dry basis) M o Initial moisture content (percent dry basis) M e Saturation moisture content (percent dry basis) A 1 Constant of an approximate solution of diffusion equation (decimal) D Effective moisture diffusivity (square meter per second) DR Diffusivity ratio B A function of W and L D av Average effective moisture diffusivity (square meter per second) t Soaking time (minutes) R i Radius of infinite cylinder (meters) R a Major radius of grain (meters) R bMinor radius of grain (meters)

Effect of Soaking Temperature on Physical and Functional Properties of Parboiled Rice Cultivars Grown in Temperate Region of India

“…There was a significant varietal difference in the color of raw brown rice kernels of different cultivars as L* value was observed to be higher in Jehlum and lower in Pusa-3 followed by SR-1, whereas a* value was higher for SR-1 (7.73) and lower for Jehlum (4.23) and b* value was higher for Koshar (26.29) and lower in SKAU-382 (22.41). The difference in color among variety of rice cultivars could be attributed to the difference in genetic makeup, colored pigments and composition of flour [2,13,14]. The effect of parboiling with the increase in temperature during soaking was observed to decrease the lightness (L*) and increase the redness (a*) and yellowness (b*) of brown rice of different varieties as reported in earlier literature [15].…”

“…Rice parboiling is a hydrothermal process consisting of soaking, heating and drying operations modifying the qualitative and processing behaviour of rice [1,2]. Soaking is a hydration process in which the diffusion controlled water uptake migrates into the rice kernel [3] and subsequent heating leads to irreversible swelling and fusion of starch granules.…”

Evaluation of physical, milling and cooking properties of four new rice (Oryza sativa L.) varieties in Nigeria

“…The difference observed in the varieties could be traced to individual properties. Different investigations also reported the wide range of grain dimensions while studying with different rice varieties (Correa, da Silva, Jaren, Afonso Junior, & Arana, 2007;Danbaba et al, 2012;Shittu, Olaniyi, Oyekanmi, & Okeleye, 2012;Mir, Bosco, & Sunooj, 2013). The length, width and thickness of the varieties are important in designing and selecting sieve separators and in calculating power during rice milling (Varnamkhasti et al, 2008).…”

Diversity of physical and cooking quality characters of selected traditional and improved rice varieties in Sri Lanka

“…Expansion of size in length-wise without increase in width during cooking is considered as a highly desirable quality characteristic rice grain. Water uptake is directly related to taste and consistency of rice and thus high water uptake indicates good quality (Shittu et al, 2012, Verma et al, 2013. The rice varieties which absorbed high quantity of water during cooking are soft varieties and these varieties which absorb low amount of water during cooking considered as hard rice varieties.…”