PROTEIN CONTENT MEASUREMENTS FOR STORED WHEAT

Authors: Casada, Mark; O'BRIEN, K - UNIV OF IDAHO,ABERDEEN,ID

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2002
Publication Date: 3/1/2003
Citation: Casada, M., O'Brien, K. 2003. Protein content measurements for stored wheat. Applied Engineering in Agriculture. 2003. 19(2):203-209.

Interpretive Summary: Wheat protein content is an important quality parameter that indicates key end-use properties. Hard wheat with low protein content may be discounted or not receive price premiums as would more desirable higher protein wheat. Producers have expressed concern that protein measurements for their wheat stored on-farm have sometimes shown sudden decreases. Since protein changes in properly stored wheat should be negligible, this study evaluated the potential for erroneous test results to give the appearance of protein content changes in stored wheat. Grain storage bins and laboratory specimens were sampled during two storage seasons to evaluate differences in protein measurements using four measurement instruments. The results showed considerable variation between the different protein measuring instruments and even more variation from individual instruments over time, with the exception of the FGIS NIR instrument. The variation over time for measurements with the FGIS instrument was only plus or minus 0.3 percent protein for an eight-month period, when measuring successive samples taken from the same locations. The greater consistency for the FGIS instrument was likely due to the rigorous standardization and calibration maintenance procedures employed by FGIS for their NIR protein instruments. Operators of other protein measurement instruments used in the wheat marketing system need to also follow a rigorous system that achieves good consistency comparable to the FGIS system. _______________________

Technical Abstract: Producers with wheat stored on-farm for a few months are concerned about surprising decreases in protein content measurements obtained from commercial laboratories. These differences can adversely affect the price when the wheat is sold. This study evaluated the contribution of measurement errors in giving a false indication of protein change during storage. Eleven bins of wheat were sampled at three locations during one storage season and five bins were sampled during the second season to evaluate differences in protein measurements. Samples were analyzed for protein content using four measurement instruments. Additional wheat was stored in the laboratory and evaluated over two years with two instruments. Data showed that the variation between protein measuring instruments was significant with an expected variation of plus or minus 0.74 percent protein content (95 % confidence interval) during the field tests. The variation over time for measurements with the FGIS instrument was plus or minus 0.3 percent protein for an eight-month period, when measuring successive samples taken from the same locations. Measurements from the other three instruments varied by plus or minus 0.8 % protein or more during the same time. Variation with in-bin location was about the same as the variation between instruments. The greater consistency for the FGIS instrument was likely due to the rigorous standardization and calibration maintenance procedures employed by FGIS for their NIR protein instruments. This indicates that a similar rigorous system is needed to obtain the same consistency for other instruments used in the wheat marketing system.