Submitted to: Journal of Agriculture and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2006
Publication Date: 8/14/2006
Citation: Parris, N., Moreau, R., Johnston, D. B., Singh, V. and Dickey, L.C., 2006. Protein Distribution in Commercial Wet- and Dry-Milled Corn Germ. Journal of Agricultural and Food Chemistry. 54:4868-4872. Interpretive Summary: Most of the oil in a corn kernel is concentrated in one portion of the kernel called the "germ" (or embryo). Corn is processed commercially by two different processes, called wet- and dry-milling. Each process fractionates the kernels into useful fractions, including the germ. The germ is extracted to produce corn oil for food uses. The protein content of the corn germ from both wet-, and dry-milling processes is usually between 14 and 16% but there is significant loss of proteins in the wet milling process. Unfortunately little information is available regarding the fate of corn germ proteins as a result of processing conditions. In an attempt to explain differences in the properties of commercial wet-, and dry-milled corn germ, we compared their protein content and distribution. We measured the total protein, acid precipitated protein and non-protein nitrogen (NPN) content of de-oiled commercial wet- and dry milled corn germ. NPN values were significantly greater for the wet- than the dry-milled germ even though their total protein content was approximately the same. We found that proteins in commercial dry-milled corn germ was similar to those found in the corn germ embryo but significantly different from proteins in wet-milled corn gem. In addition the amount of protein was significantly less in wet-compared to dry-milled corn germ. Results from this study will benefit food scientists and engineers by providing information on obtaining higher quality corn germ proteins with less loss as a result of processing and on the development of higher valued co-products.
Technical Abstract: In order to identify high valued co-products from commercially processed corn germ, it was necessary to determine the affect of processing conditions on corn germ proteins. We found that significantly less protein was extracted from commercial wet- compared to dry-milled corn germ using Tris, SDS buffer containing 14 mM 2-mercaptoethanol at 100 degree C for 10 min. SDS-PAGE revealed a number of proteins with molecular weight ranging from approximately 10 to 66 KDa for the dry-milled corn germ compared to only a few significant protein bands centered around 23 KDa in the wet-milled corn germ. Total protein content of the wet-, and dry-milled corn germ was approximately the same however non-protein nitrogen values were significantly greater for the wet-, than the dry-milled germ. The protein profile of germ embryo, freshly hand-dissected from yellow dent corn kernels was more similar to that of dry-, than wet-milled corn. SDS PAGE of laboratory preparations of wet-milled corn germ more closely resembled commercial dry- than wet-milled corn germ which could be attributed to limited microbial growth in the laboratory preparations.