Effect of brown rice temperature in polishing stage on rice milling quality.
2005
Saboori, Samad | Rafiee, Nader | Shard, Ali
A causative factor for breaking of rice kernels during whitening process could be assumed to be produced heat in a whitener because of abrasion and friction of grains by themselves and / or to cone and concave. An investigation conducted in order to study the effect of produced heat on rice kernels breaking with respect to different temperatures of brown rice in whitening process. An improved rice cultivar named khazar selected for experiments. Rough rice samples dried up to moicture content of 10-11 percentage on w.b. . Then, they were hulled within 90±2% by a rubber roll husker. All the samples were packed in plastic bags and retained in temperatures of –13, 5, 18, 15, 35, 45 and 55cْ . Whitening was also performed by a pilot friction type whitener at three different periods of 30, 35 and 40 seconds. Factorial experiment with two factors of brown rice temperoture and whitening period based on compeletely randomoized design was choosen in six replications. The results revealed that a tempenature rice up to 25cْ had no significant effect on milled rice yield, however there was a decrease in temeratures higher than 25cْ so that it reduced to 1.94% when temperature increased to 55 c. Keep rising in temperature led to more broken grains percentage particulary it wsa abowt 3.7% when temperature rose from 25 to 55 c. Percentage crack variations wsa not significant in all treatments as well. The lowest brightness index was observed when temperatures were in the range of 5-25 c, whereas there were higher indices in temperatures of – 13 or above 25 c. Key words: brown rice temperature , rice whitening or polishing , rice breakage , rice milling
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