Combination soaking procedure for rough rice parboiling
2005
Igathinathane, C. | Chattopadhyay, P.K. | Pordesimo, L.O.
Soaking of rough rice is the most time-consuming operation in the parboiling process. A combination soaking procedure for parboiling of rough rice was developed based on the gelatinization temperature of rice starch to achieve rapid completion of soaking. The objectives of this study were to determine the gelatinization temperature of rice starch, the soaking characteristics of the rough rice, and prescribe the operating parameters of the combination soaking procedure. Medium-grain rough rice ('Pankaj') was selected, and its starch gelatinization temperature was determined as 72 degrees C using alkali degradation and hot stage microscopy methods. Soaking characteristics of rough rice were studied at 60 degrees C, 70 degrees C, and 80 degrees C. Below the gelatinization temperature, soaking proceeded in the normal way; however, above the gelatinization temperature, excessive water absorption, husk splitting, actual cooking of rice kernels, and loss of quality due to soak water contamination were observed. The combination soaking procedure, involving 80 degrees C water as the first stage until an intermediate moisture content of 35.0% d.b. (approx. 45 min) followed by 70 degrees C as the second stage up to the saturation moisture content of 42.7% d.b. (approx. 3 h 15 min), resulted in a 67% time reduction when compared with single-stage soaking at 70 degrees C. Rice from the combination procedure resembled that obtained from 70 degrees C single-stage soaking in all respects. In milling analysis, after parboiling the rough rice from both soaking methods, the polished rice did not show any difference in terms of head rice yield, broken grains produced, and cracked grains produced.
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