New Techniques for Improved Shelf Life of Rough & Brown Rice, 2013


Project Leader

Ruihong Zhang, professor, Dept. of Biological and Agricultural Engineering, UC Davis

Infrared heating has shown great promise to improve rice drying efficiency, the milling quality of rough rice, and the stabilization of rice bran. In 2013 this project continued investigation of the effects of infrared heating and tempering on rough rice, rice bran, and rice bran oil.

Infrared treatment of rough rice
Extracted oil from treated and untreated rice bran. (NT: no tempering, WT: with tempering)
Percentage moisture removed in rough rice under infrared heating.

Freshly harvested samples of M-206 rice were obtained from Farmers’ Rice Cooperative. Samples were split into three equal portions. The first portion was heated with infrared to a surface temperature of 140 degrees Fahrenheit, followed by tempering for four hours and then natural cooling. The second and third portions were dried with hot and ambient drying methods, respectively.

Each of the dried samples was divided into two portions. One was used as rough rice and the other was dehusked to produce brown rice. The rough rice and brown rice samples were stored at “accelerated” storage conditions (95 degrees Fahrenheit and 65% relative humidity) for four months. Milling quality and degradation in lipids were evaluated during the storage time.

To study rice bran stability and quality of rice bran oil, the ambient air-dried rough rice sample was dehusked and milled to produce rice bran. Rice bran samples were then heated to 140, 176, and 212 degrees Fahrenheit with infrared heating. The samples were tempered in closed containers in an incubator for four hours. Samples were cooled naturally to room temperature and then stored for 29 days. Samples were evaluated for the stability of treated bran and the quality of extracted rice bran oil.

 This research clearly revealed that a high drying rate and good milling quality can be achieved by heating rice to about 140 degrees Fahrenheit with infrared, followed by tempering and natural cooling. Moreover, results show that brown rice stability can be improved during storage by heating rough rice with infrared to 140 degrees Fahrenheit, followed by tempering and natural cooling. Enhanced stability of brown rice could lead to increased storage capacity, reduced energy use, and increased consumption. Additionally, infrared heating of rice bran, followed by tempering for four hours, inactivates lipase enzymes and thus extends storage time to more than four weeks.

These results indicate that infrared heating and tempering can be used as an efficient alternative to conventional heating methods. However, further study is needed to investigate the effects of infrared heating and tempering treatments on brown rice storage under ambient conditions and to evaluate the cooking and sensory quality of treated brown rice. Also, infrared heating followed by tempering to control enzyme activity could lead to new processing methods to obtain edible oil from rice bran.