Detection of fragments from internal insects in wheat samples using a laboratory entoleter

Authors: Brabec, Daniel - Dan; Pearson, Thomas; Maghirang, Elizabeth; Flinn, Paul

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/21/2014
Publication Date: 1/1/2015
Publication URL: http://cerealchemistry.aaccnet.org/doi/abs/10.1094/CCHEM-08-13-0173-R
Citation: Brabec, D.L., Pearson, T.C., Maghirang, E.B., Flinn, P.W. 2015. Detection of fragments from internal insects in wheat samples using a laboratory entoleter. Cereal Chemistry. 92(1):8-13. DOI: http://dx.doi.org/10.1094/CCHEM-08-13-0173-R.

Interpretive Summary: Grain in storage is vulnerable to insect infestation that can lead to insect fragments in flour, which are regulated by the Food and Drug Administration. To date, there are no economically viable methods for detecting grain that may be infested by insects that live most of their life inside the kernels and to estimate the number of insect fragments that would be present when the grain is milled. This study demonstrated the use of a small mechanical device which breaks open infested kernels and releases the infesting insect, while leaving approximately 98% of the un-infested kernels intact. The insects that are released from the broken kernels can then be easily counted after sieving the wheat sample to separate the broken pieces from the whole kernels. The method is simple, does not require chemicals or supplies, and takes approximately five minutes per 500g grain sample. The amount of insect pieces counted after sieving was found to have a high correlation with expected insect fragments if the grain were milled. Detection of grain samples infested at levels well below the FDA limit of 75 insect fragments per 50g/flour are possible. Samples of grain infested at levels corresponding to as few as four insect fragments per 50g/flour can be detected. As such, the method can find use at many grain receiving stations to better ascertain the level of insect infestation in grain, and by grain storage managers to better learn effective timing of fumigations and insect mitigation procedures.

Technical Abstract: A simple, rapid method was developed for estimating the number of insect fragments in flour caused by hidden, internal-feeding insects in whole grains during storage. The method uses a small mechanical rotary device (entoleter), which accelerates whole wheat kernels to high speeds and projects them onto an impact surface. By adjusting entoleter impeller speed based on grain hardness and moisture content, this process results in grain that is 98% intact and 2% broken. Insect-infested kernels are weaker due to tunnels created by feeding, thus, they break apart more readily and release the infesting insect upon impact. At entoleter impeller speeds resulting with 2% grain breakage, the infesting insects remain as larger fragments, which can be quickly counted after sieving. Results showed that 70 to 90% of the infested kernels break apart using this procedure. Known counts of pre-emergent adult, pupae and larvae of lesser grain borers and rice weevils were blended with 500-g samples of un-infested hard red winter and soft red winter wheat. The estimated fragments in 50-g flour samples that would result if the sample were milled were computed using data from previous studies that showed how many insect fragments of lesser grain borers and rice weevils produce when milled. Samples were infested at levels that would correspond to approximately 20 to 100 insect fragments in 50 g of flour. The bulk sample was processed in the entoleter and sieved, and the numbers of insect pieces were then counted. Two sieve sizes were used: (a) #10 sieve which separated most of the broken kernels and insect fragments from whole kernels and (b) #20 sieve which separated smaller fragments from larger fractured grains and insects. These counts were found to correlate with the estimated insect fragments in flour with an R2 value of 0.94, and the predictions were not affected by the grain hardness, moisture, or insect species. Furthermore, the method appears to distinguish samples of whole grain that would contain 0, 25, or 75 insect fragments in milled flour, with greater than 95% confidence. The method can be performed in approximately 5 minutes per 500-g samples, does not require chemicals, and could potentially be a cost-effective method for grain handlers to inspect loads for insect damage and the potential estimation of insect fragments in flour.