COMBINATION SOAKING PROCEDURE FOR ROUGH RICE PARBOILING
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°C using 
alkali degradation and hot stage microscopy methods. Soaking characteristics of rough rice were studied at 60°C, 70°C, and 
80°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°C water as the first stage until an 
intermediate moisture content of 35.0% d.b. (approx. 45 min) followed by 70°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°C. Rice from the combination procedure resembled that obtained from 70°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.