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Effect of soaking temperature on the healing of fissured rough rice kernels
E. LII (1), W. Domingues (1), J. Patindol (1), Y. Wang (1) (1) University of Arkansas, , U.S.A..

Internal stresses due to moisture and temperature gradients often result in the development of rice kernel fissures. Fissured rough rice kernels tend to break upon milling and potentially reduce the market value of rice. This work was conducted on the premise that kernel fissures may be healed by soaking in water at a specific temperature and duration. Fissured rough rice kernels of a long-grain cultivar, Wells (with a moisture content of ~12% and an onset gelatinization temperature of 73.0°C), were selected by X-ray imaging using a tabletop digital radiography system. Fissured kernels were soaked in a water bath at five soaking temperatures (60, 65, 70, 75, and 80°C) and three soaking durations (1, 2, and 3 h). Soaked kernels were then gently dried to a constant weight at 26°C and 65% relative humidity for characterization. Digital X-ray images revealed that soaking at 75°C for 3 h healed up to 70.0% of the fissured kernels. Soaking at 60°C did not result in healing; fissures even worsened on the lots soaked for 1-2 h. Soaking at 65 or 70°C for 3 h healed 17.5% of the fissures; healing did not occur on the lots soaked for 1-2 h. Soaking at 80°C for 2 h resulted in 35.0% healing; the lot soaked for 3 h turned mushy, hulls split, some particles leached into the soaking water, and was not subjected to X-ray imaging. Bending tests using a texture analyzer showed that brown rice kernel breaking force increased from 12.0 N of fissured kernels to 43.5 N of healed kernels. Soaking rough rice in water at a temperature slightly above its onset gelatinization temperature may potentially repair fissures.