Detection of internally infested popcorn using electrically conductive roller mills

Authors: Brabec, Daniel - Dan; Dowell, Floyd; Campbell, James - Jim

Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2016
Publication Date: 12/1/2016
Publication URL: https://handle.nal.usda.gov/10113/5814435
Citation: Brabec, D.L., Dowell, F.E., Campbell, J.F. 2016. Detection of internally infested popcorn using electrically conductive roller mills. Journal of Stored Products Research. 70:37-43. doi:10.1016/j.jspr.2016.11.002.

Interpretive Summary: Rapid detection of insect pests that develop inside grain is a real challenge for the grain, milling and food processing industries, since there is little external sign of infestation. ARS scientists developed a conductive roller mill to detect insect infested seeds by grinding the grain using a pair of grinding rolls with a low voltage connection across them to detect changes in circuit resistance when insect infested seeds are ground. Modifications to the conductive mill to be able to detect maize weevil infestations of popcorn were developed and enabled the mill to grind 1 kg of popcorn in about 2 minutes. The mill was able to detect 80%-90% of the medium and large insects (late stage larvae, pupae, and adults). Detection of smaller internal stages was more difficult, with ~50% or less detected. The conductive roller mill provided rapid processing and reasonably high detection effectiveness and could be used a useful tool for industry stakeholders in their evaluation of grain during inbound inspection and during storage.

Technical Abstract: To detect popcorn kernels infested by the internal feeding stored-product insect pest Sitophilus zeamais, maize weevil, a laboratory roller mill was modified so that the electrical conductivity of the grain is measured while the kernels are milled between the rolls. When a kernel with a S. zeamais larvae inside is milled, the moisture from the crushed insect abruptly changes the conductivity of the test circuit. The objective of this study was to determine the potential of the modified conductance mill to detect popcorn infested with different developmental stages. Two laboratory milling units were tested that had differing sharpness, which affected the feed-rate through the rolls. One mill averaged 135 seconds to feed 1kg of popcorn while the second mill with sharper teeth averaged 100 seconds to feed 1kg of popcorn. Four popcorn varieties were evaluated, with their average kernel weight ranging from 12.5g to 18.5g per 100 kernels. Known numbers of infested popcorn kernels were added to 1kg samples of popcorn. The slower feeding mill detected 81% of the pupae, 91% of the medium larvae, and 47% of the small larvae. The faster feeding mill detected 75% of the pupae, 80% of the medium larvae, and 43% of the small larvae. Our results indicate that the conductance mill is a good method for quickly evaluating popcorn samples for kernels infested with late stage larvae and pupae.