Submitted to: Journal of Agricultural Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2013
Publication Date: 3/18/2013
Publication URL: http://handle.nal.usda.gov/10113/56121
Citation: Pearson, T.C., Maghirang, E.B., Dowell, F.E. 2013. A multispectral sorting device for wheat kernels. Journal of Agricultural Science and Technology. 2:45-60.
Interpretive Summary: Light measured in different spectral bands allows us to differentiate colors and, if some of the spectral bands are near infrared, we can ascertain biochemical properties of materials. However, high speed measurement of enough different spectral bands has been difficult to accomplish. In this study, a low cost electronic sorting system was developed to quickly pulse different light emitting diodes (LED) to illuminate individual grain kernels as they slide off a chute. Each LED emits light from a different spectral band, thus providing a multi-spectral light source. Additionally, the device measures the pulsed light reflected from the kernels, facilitating rapid measurement of light at several different spectral bands. Both visible and near infrared LEDs were used so that detection and segregation of kernels with different colors and biochemical properties can be made. The sorting system was tested for its ability to separate red and white wheat, fungal infected wheat, and wheat kernels with high protein content. The system was able to separate red wheat from white wheat with an overall accuracy of 87% and separated fungal infested grain with 94% accuracy. For the protein sort tests, the sorter increased the protein content of wheat by an average of 1% by isolating 40% of the original wheat that had higher protein content. These results are comparable to other laboratory sorting equipment but this new system is low cost (parts for a complete system are about $1000) and is able to sort at rates of about 2Kg/hr. This system should find many uses for segregating breeder samples for desirable traits, leading to higher quality crops.
Technical Abstract: A low-cost multispectral sorting device was constructed using three visible and three near-infrared light-emitting diodes (LED) with peak emission wavelengths of 470 nm (blue), 527 nm (green), 624 nm (red), 850 nm, 940 nm, and 1070 nm. The multispectral data were collected by rapidly (~12 kHz) blinking one LED at a time and subsequently measuring the reflected light from wheat kernels as they dropped off a feeder chute. A low-cost microcontroller was used to direct the LED pulses, digitize the analog signal from the photodiode, perform signal processing, and apply classifications. The sorting was accomplished by the activation of an air valve that diverted the wheat kernels per the classification assignment. Three applications were tested; the separation of red from white wheat kernels, the separation of Fusarium head blight (FHB)-damaged kernels from undamaged kernels, and the separation of kernels classified as having high, medium, and low protein content. The performance of this LED-based sorter was compared with those of a high-speed color image-based sorter and a single-kernel near-infrared reflectance (SKNIR) sorter (950-1650 nm). The results indicate that the accuracy of the LED-based sorter was comparable to or better than the color image-based sorter. For the sorting of red from white wheat, the LED-based instrument removed 98% of the white wheat while also removing 23.7% of the red wheat in two subsequent passes. In contrast, the color image-based sorter removed less white wheat (83%) while removing more of the red wheat (42.4%). For FHB-damaged kernels, both the LED- and color image-based sorters removed approximately 90% of the kernels with visible symptoms of FHB-damage. However, the LED-based sorter removed fewer undamaged kernels (1.9%) compared to the color image-based sorter (7.0%). For isolating kernels with high protein content, both the LED and color image instruments diverted ~40% of the original wheat sample, which contained ~1.0% higher protein content on average than the original sample. However, the LED sorter was more consistent in isolating the higher-protein kernels across seven different varieties of hard red winter wheat. In comparison, the SKNIR sorter yielded a 1.9% increase in protein content compared with the original unsorted wheat sample. The throughput of the LED sorter was approximately 20 kernels/s compared with ~200 kernels/s for the image sorter and ~0.5 kernels/s for the SKNIR sorter. The cost of the LED-based sorter is expected to be less than either of the other two instruments; in total, the parts for the construction of the LED-based sorter cost approximately $1000. The LED-based sorter will likely be most effectively employed to separate the desired traits of small lots of seed (e.g., breeder size samples), assist in sample purification, and help breeders in selecting the kernels with higher protein and less damage due to FHB.