Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/14/2007
Publication Date: 3/1/2008
Citation: Sheperd, C.T., Vignaux, N., Peterson, J.M., Scott, M.P., Johnson, L.R. 2008. Dry-milling and Fractionation of Transgenic Maize Seed Tissues with Green Fluorescent Protein as a Tissue Marker. Cereal Chemistry. 85:196-201. Interpretive Summary: The grain of corn is composed of different tissues with different chemical compositions. One way to increase the value of grain is to mechanically separate it into fractions that are better suited to different end uses than ground, whole grain. This process is called milling. One way to evaluate milling performance is to determine the amount of each grain tissue in each fraction produced by milling. This is difficult to do because tissue specific markers are either difficult to quantify or not really tissue specific. We developed maize lines that produce grain containing the readily quantifiable protein GFP in different grain tissues. By milling this grain and measuring the GFP fluourescence in the resulting fractions, we were able to calculate the amount of each grain tissue in each fraction. This approach can be used to optimize grain milling for recovery of certain tissues. Optimal milling procedures will decrease the cost of production of grain milling products, benefitting the milling industry and consumers.
Technical Abstract: The efficiency of fractionating cereal grains (e.g., dry corn milling) can be evaluated and monitored by quantifying the proportions of seed tissues in each of the recovered fractions. The quantities of individual tissues are typically estimated using indirect methods such as quantifying fiber or ash to indicate pericarp and tip cap contents, and oil to indicate germ content. More direct and reliable methods are possible with tissue-specific markers. We used two transgenic maize lines; one containing the fluorescent protein Green Fluorescent Protein (GFP) expressed in endosperm and the other containing GFP expressed in germ to determine the fate of each tissue in the dry-milling fractionation process. The two lines were dry-milled to produce three fractions (bran-, endosperm-, and germ-rich fractions) and GFP fluorescence was quantified in each fraction to estimate the tissue composition. Using a simplified laboratory dry-milling procedure and our GFP-containing grain, we determined that the endosperm-rich fraction contained 4% germ tissue, the germ-rich fraction contained 28% germ, 20% endosperm, and 52% non-endosperm and non-embryo tissues, and the bran-rich fraction.