New Techniques for Stabilization of Rice Bran, 2013

 

Project Leader

Zhongli Pan, research engineer, USDA Agricultural Research Service, Albany, CA

The goal of this project is to develop alternative techniques for stabilizing rice bran. Alternatives are needed to replace heating methods such as hot air, drum drying, and dry extrusion—all commonly used in the rice industry. These techniques subject rice bran to severe and nonuniform heating, which damages valuable rice bran components and also results in high energy consumption. Infrared, ultraviolet, and pulsed electric field are technologies with the potential to be used in rice bran stabilization.

Freshly harvested M-206 rice was obtained from Farmers’ Rice Cooperative for this research. Initial moisture contents of rough rice samples ranged from 20.7% to 32.5%. In the first treatment, samples were heated with an infrared device to 140 degrees Fahrenheit, followed by tempering in closed containers from one to five hours. In the ultraviolet experiment, rough rice samples were air dried and then dehusked before being exposed to treatments of 10, 20, and 30 minutes. In the pulsed electric field experiment, rice bran samples were treated under different pulse numbers and frequencies.

To evaluate the effectiveness of treatments on rice bran stabilization, free fatty acid concentrations were measured to determine the level of enzyme (lipase) inactivation over storage periods ranging up to 38 days. To evaluate milling quality, treated and untreated rice samples were milled three times to determine effects on total rice yield, head rice yield, and whiteness index.

The results showed that high drying rates, good milling quality, and effective enzyme inactivation could be achieved with a short infrared heating time (less than a minute), followed by at least three hours of tempering. Total moisture removal after tempering and cooling was 5.6% and 12.2% for one and two drying passes, respectively. The tempering process is essential to achieve high milling quality, to improve moisture removal during cooling, and to enhance enzyme inactivation.

The ultraviolet and pulsed electric field treatments did not have a significant impact on enzyme inactivation. Therefore, the infrared treatment of rough rice followed by tempering for at least three hours is recommended. This is an effective approach to inactivate enzymes and extend the storage stability of rice bran for up to 38 days after milling. Infrared treatment also results in high drying rates and good milling quality.

Optimization of the process and the effect of infrared heating on the storability of brown rice and the quality of rice bran oil need to be investigated further. These findings can lead to new approaches to rice bran stabilization and utilization.