Distribution of Cadmium, Iron, and Zinc in Millstreams of Hard Winter Wheat (Triticum aestivum L.).

Hard winter wheat (Triticum aestivum L.) is a major crop in the Great Plains of the United States, and our previous work demonstrated that wheat genotypes vary for the propensity to accumulate cadmium in grain.  The few prior reports of the fate of cadmium in flour milling have not evaluated high cadmium grain (> 0.2 mg kg^-1).  This study measured the distribution of cadmium, zinc, and iron in flour and bran streams from high cadmium grain (0.352 mg kg^-1) milled on a long flow experimental flour mill that produced twelve flour streams and four bran streams.  Concentrations of cadmium, iron, and zinc in the millstreams were highly correlated (r > 0.98).  Cadmium was stored primarily as insoluble complexes in both flour and bran.  Recovery in flour streams, as a fraction of total recovery, was substantially greater for cadmium (50%) than for zinc (31%) and iron (22%).  Cadmium, zinc, and iron concentrations in the lowest mineral concentration flour stream were 52%, 22%, and 11%, respectively, of the initial grain concentration.  Milling wheat grain to white flour removed greater fractions of zinc and iron than cadmium.  Our results indicate that, relative to zinc and iron, a greater proportion of cadmium is stored in the central endosperm of the wheat kernel.  The results of this study reinforce the importance of developing low-cadmium bread wheat cultivars through breeding to serve regions that produce grain on high cadmium soils.