Research into rice utilization and product development moved into a new area in 2004.  With the planned decommissioning of currently licensed pesticides, a safe, non-chemical alternative to eliminate pests from harvested paddy rice is needed.  Scientists examined two different thermal treatment methods — infrared and radio frequency — at the USDA Agricultural Research Service in Albany and at the Crocker Nuclear Laboratory at UC Davis.

Control of the Angoumois grain moth (center) was the subject of new research

The Angoumois grain moth (Sitotroga cerealella) exists naturally in harvested rice.  Two different storage samples of M-202 rice at about 13 percent moisture were used in the study.  In one approach samples were heated with infrared to temperatures ranging from 45 to 70 degrees centigrade (139 to 184 degrees Fahrenheit) and held for times ranging from one to 10 minutes.  Rice samples were also heated with radio frequency to temperatures ranging from 35 to 70 degrees centigrade (121 to 184 Fahrenheit) and held there for five to 40 minutes.

The effectiveness of these treatments was determined by counting emerging adult insects every two to three days during an extended observation period.  If no live adult insects were observed after 42 days (about two insect life cycles), the treatment was deemed effective since the insects in all forms would have been disinfested.  Moisture loss and its potential impact on milling quality were also examined.

Research results indicate that both infrared and radio frequency could be used to disinfest stored paddy rice.  The required temperature and holding times were 50 degrees centigrade (148 degrees Fahrenheit) for one minute for infrared and 60 degrees centigrade (166 degrees Fahrenheit) for five minutes with radio waves. 

At these thresholds, rice-milling quality was not significantly affected.  However, the infrared technique caused about one percent moisture loss.  The most moisture loss occurred during the three-minute heating and could be minimized by increasing heating rate with reducing rice bed thickness (see figure) and increasing the heating intensity.  No significant moisture loss for rice samples treated with radio frequency was observed under test conditions.

Based on available information, both of these techniques are economically feasible with projected electric costs less than $2 a ton for radio frequency treatment. Further research is needed to optimize the treatment methods and to conduct a detailed feasibility analysis.