Effect of Protein Disruption Using Proteolytic Treatment on Cooked Rice Texture Properties

Two long-grain rice (Oryzae sativa L.) cultivars (Wells and Francis) were harvested from Stuttgart, AR and Essex, MO at high (21.0–22.0%) and low (12.8–16.3%) moisture contents (MCs). Rice samples were soaked in distilled water, sodium phosphate buffer and sodium phosphate buffer with a 0.2% protease (PS) at 37C for 30 min before cooking. A uniaxial compression test was performed to assess cooked rice texture properties. Results showed that protease treatment resulted in a significant decrease in cooked rice firmness for all cultivars across harvest locations and harvest MC. This indicated that proteins were involved in providing structural support to the rice kernel during cooking, restricting starch granule swelling and water hydration. The increase in cooked rice MC after PS treatment provides support for this finding. Stickiness significantly (P < 0.05) increased by soaking either in water or buffer solutions. This was attributed to a greater solubilization of starch, especially amylose leaching, during cooking. Protease treatment did not significantly increase cooked rice stickiness over the buffer treatment. PRACTICAL APPLICATIONS The structural integrity of a rice kernel plays an important role in determining the textural properties of cooked rice. This study demonstrated that protein (i.e., through its disruption using protease) as well as lipid and starch (i.e., removal of starch and lipid during the draining and washing steps) all contribute in determining cooked rice texture properties. Results from this study indicated the possibility of reducing rice cooking duration to achieve texture properties similar to that with no protease treatment. Moreover, 1 Corresponding author. TEL: 479-575-6822; FAX: 479-575-6936; EMAIL: [email protected] Journal of Texture Studies 38 (2007) 423–437. All Rights Reserved. © 2007, The Author(s) Journal compilation © 2007, Blackwell Publishing 423 sticky rice products can be produced by protease treatment of rice before cooking.