|Rice Utilization and Product
Development - 2005
Project Leader and Principal UC Investigators
Zhongli (John) Pan,research engineer, USDA/ARS, Albany, CA
This project is continuing research begun in 2004 to find a safe, non-chemical method of eliminating insect pests from rough rice. Two thermal techniques—infrared and radio frequency heating treatments—showed promise in previous research. The 2005 experiments with both types of treatment had three primary objectives:
In the first part of this research, commercially obtained samples of M-202 at 11 percent moisture content were infested with lesser grain borers and with Angoumois grain moths. Adult insects were introduced into the sample at 18 and six days before infrared treatment to produce eggs and larvae in the sample. In the radio frequency experiment, adult beetles and moths were introduced into a large sample of storage rice about a month before treatment.
Rice was run through a pre-heated drying bed as a single layer to limit moisture loss during treatment—a modification from the previous year. This technique resulted in rapid heating of rice with reduced moisture loss. For example, it took only 20 seconds to heat the rice sample to 166 degrees Fahrenheit with a half percent moisture loss. In the previous year, where rice was not spread as thinly, moisture loss was 1.5 percent. Infrared heating did not cause any significant changes in rice milling quality. Minimum disinfestation requirements were to heat rice to 153 degrees Fahrenheit, followed by a 20-minute tempering to control moths, and 166 degrees Fahrenheit, followed by a 20-minute tempering to control beetles.
In the radio frequency treatment, conditions for killing all forms of the moth were to heat rice to 148 degrees Fahrenheit, followed by a two-hour tempering; 157 degrees Fahrenheit, followed by a one-hour tempering; or 166 degrees Fahrenheit, followed by a 30-minute tempering. Similarly, the minimum required treatments for killing all forms of beetles was to heat the rice to 166 degrees Fahrenheit, followed by a one-hour tempering. Since this treatment took place in a closed container, no moisture loss occurred during heating. The rice treated with radio frequency had superior milling quality compared to untreated samples.
Freshly harvested samples of M-202 at 25 percent moisture were used to determine whether infrared drying and insect disinfestation could successfully take place simultaneously. Part of this sample was dried gradually to 20.6 percent moisture without using heat. Both samples were infested with adult beetles and moths four days before treatment. The disinfestation results of freshly harvested rice were similar to the storage rice. Beetles were more heat resistant than moths. Satisfactory disinfestation took place on a pre-heated drying bed in 60 seconds at 162 degrees Fahrenheit in freshly harvested rice samples at both moisture levels. Moisture removal was 1.7 percent to 1.8 percent during heating. When rice samples were tempered for another four hours following heating, an additional 1 percent to 1.4 percent moisture was removed during cooling. Thus, total moisture removal ranged between 2.7 percent and 3.2 percent.
Researchers conclude that both infrared and radio frequency treatment can be used for disinfestations of storage rice without lowering milling quality, but infrared heating could cause about a half percent moisture loss during heating. Infrared heating can also be used for simultaneous drying and disinfestation with high heating and drying rates.