Abstract
A process of removing thinner kernels of rough rice, i.e., thickness fraction process, has been suggested as a method for increasing milling yields in the rice industry. This study aimed at determining whether physicochemical properties, cooking qualities, and sensory characteristics of rice samples could be changed by the addition of a thickness fraction into the rice process stream. Each of four long-grain rice cultivar lots was assigned into two groups: unfractionated and thickness-fractionated. For the thickness-fractionated group, thin rice kernels (<1.9 mm) of rough rice were discarded from unfractionated rice samples. Unfractionated and thickness-fractionated rice samples were compared with respect to physicochemical properties, cooking qualities, and sensory characteristics. The results showed that the removal of such thin kernels decreased the breakage and chalkiness rates and increased head rice yields. Fractionated rice samples exhibited lower amylose contents and crude protein contents but higher gelatinization temperatures than unfractionated rice samples. While the optimum cooking duration and width–expansion ratios of thickness-fractionated rice samples were higher than those of unfractionated ones, there was a negligible impact of the thickness fraction process on sensory characteristics of long-grain rice samples. In conclusion, the thickness fraction process affects physicochemical properties and cooking qualities more than the sensory characteristics of rice samples.
Highlights
Thickness fraction, known as thickness grading, of rough rice, refers to a process through which rough rice is first screened according to size into different thickness fractions, and the thinner kernels are removed for other applications such as flour or parboiling [1]
The thickness fraction of rough rice resulted in thick fractions ranging from 34% to
Cheniere, where the final viscosity was significantly higher in the fractionated portion compared to the unfractionated portion of the same cultivar. These results suggest that genotypic variance in final viscosities and setbacks must be considered when a thickness fraction process is included, and selection of a cultivar for further size fraction should be performed on the basis of the functional properties and end applications of the rice
Summary
Known as thickness grading, of rough rice, refers to a process through which rough rice is first screened according to size into different thickness fractions, and the thinner kernels are removed for other applications such as flour or parboiling [1]. Chen et al [4] observed that the thinnest rice kernels (1.49 mm) after milling under identical conditions. These results suggest that the pressure to which rice is subjected during milling, or the duration of the milling procedure will result in the thinnest kernel fraction being milled at a greater bran removal rate than the other kernel fractions. If thinner rice kernels are separated from thicker kernels and milled separately, breakage rates could be reduced, resulting in higher milling yields
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