Working out the bugs
May 01, 1995
by Teresa Acklin
Research in the U.S. and U.K. offers promising new solutions to the old problem of insect detection in grain.
Detecting insects in grain poses one of the peskiest problems in the cereals industry. Decisions on the value of grain, possible control measures and even end uses depend on accurately detecting previous and existing infestations.
Yet most traditional methods of insect detection in whole grain and milled grain products typically have been either imprecise or too costly for widespread industry use. Visual inspections are economical, but do not necessarily provide complete and reliable information; and in whole grain, visual methods cannot warn of insects developing inside the kernels. Analysis by x-ray, although more accurate, requires expensive and environmentally sensitive equipment, as well as specialized skills to interpret the pictures.
For many years, researchers throughout the world have dedicated their efforts to overcoming these problems, with a goal of devising fast, reliable, comprehensive, sturdy and inexpensive systems to detect insects and to quantify the nature and extent of contamination. In at least two countries, scientific groups recently have made some promising strides toward solving this age-old problem.
PASSING THE LITMUS TEST.
In the United States, research at the University of Texas at Austin has focused on an ELISA test detecting insects in grain by identifying the presence of an insect protein (see World Grain, April 1993, page 13).
The project, funded in part by the U.S. Millers' National Federation and the U.S. Department of Agriculture, is led by G. Barrie Kitto, professor of chemistry and biochemistry and director of the Center for Biotechnology at Austin, in collaboration with U.S.D.A. researchers.
The assay procedure, called “Insect-Detect,” has attracted attention in the past few years as a precise and reliable method for quantitatively determining the degree of contamination, Dr. Kitto said. The test works equivalently with all of the major insect species found in grain and with all types of grain.
But the formal procedure requires special equipment and technical skills common to a quality control laboratory, making it unsuitable for use “in the field.” The grain industry pressed for a procedure that could be widely used at grain loading and unloading facilities or for spot-checking export/import cargoes.
In response, Dr. Kitto and his colleagues developed a very simple test-strip assay. The guiding principles were that the design should be simple to use with absolutely minimal training and equipment, while retaining the same sensitivity and applicability as the laboratory test.
The test strip assay is in effect a “litmus test.” Fifty grams of grain are ground and extracted in a simple household blender, and a sample of the extract is applied to the test strip. After a short incubation, the strip is rinsed and placed in contact with a developing solution for five minutes.
A blue color appears in proportion to the amount of insect material present in the test grain sample. The degree of grain contamination can be evaluated by comparing the test-strip with a standard color swatch.
If desired, a more precise measurement of contamination can be obtained by inserting the test strip into a small, battery operated hand-held colorimeter. The whole procedure can be completed within about 15 minutes, and several samples can be tested at the same time.
The University of Texas and private investors have formed a joint venture company, Biotect, Inc. in Austin, to commercialize the test strip. Trial kits have been sold in the U.S., Australia, Japan, Israel, the U.K. and China.
NIR TO THE RESCUE AGAIN.
Scientists in the U.K. have made significant progress in developing an insect detection system based on near-infrared spectroscopy. NIR technology already has proved its worth to the grain and processing industries through its use in measuring moisture and protein levels.
Funded by the U.K.'s Home-Grown Cereals Authority, the NIR insect project began in October 1991 at the Central Science Laboratory of the Ministry of Agriculture, Fisheries and Food. The H.G.C.A. also provided grants to two companies, NIR Systems and ADAS, who collaborated on the project.
The project's goal was to discover whether a “robust” or field-sturdy NIR system could be developed that would detect insects at population densities of one insect per kilogram or less. A handful of earlier studies had indicated NIR technology could detect flour mites in animal feed and beetles in small samples of unmilled wheat, and the Central Science researchers hoped to build on those preliminary findings.
To conduct their research, the scientists used saw-tooth grain beetles, grain weevils and different wheat varieties to conduct a number of experiments. Tests involved measuring the differences in the spectra, or wavelengths of light, between uninfested grain and grain containing live and dead adults, immature insects and insects inside the grain kernels.
The research showed conclusively that NIR is capable of detecting different species of insects in different developmental stages in different wheat varieties and at different moisture levels. The NIR process is extremely fast; scanning, data recording and analysis take no more than a few seconds.
A surprising discovery was that the NIR technique is able to detect grain kernels with internal infestation. The NIR measurements on internal insects were “genuine, reproducible and well-defined,” according to the project report.
The experiments also determined that the NIR reflectance technique, or a beam reflecting off the sample, was preferable to NIR transmittance, or a beam passing through the sample. The addition of an aluminum foil backing enhanced the reflecting performance, permitting detection of insects on the far side of a 1 centimeter thick sample.
At this point, the technique has not yet been commercialized because the process does not consistently detect insects at the one-per-kg level deemed low enough for trade use. But the researchers noted recent developments in NIR hardware should enable the technique to reach that threshold in the not-too-distant future.
Eventually, the researchers hope all the NIR techniques for the grain industry can be combined into a single apparatus to simultaneoulsy measure insects, protein and moisture.