C. R. Jones, J. R. Fraser, and T. Moran. Copyright 1960 by the American Association of Cereal Chemists, Inc.
The thiamine content of the fine (0-17 microns) fraction, obtained by air-classifying a flour laboratory-milled from soft English wheat, was similar to that of the initial flour, while those of the medium (17-35 microns) and the coarse (over 35 microns) fractions were respectively rather lower and rather higher. With corresponding fractions from a hard English wheat, on the other hand, the value for the fine fraction was much higher and that for the coarse rather lower. The effect of grinding the flour with pinned disks, prior to air-classification, was to reduce the thiamine content of the coarse fraction and, in the case of the soft flour, to raise markedly that of the fine fraction. With the hard flour, the high thiamine content of the fine fraction was maintained, while (as with the soft flour) the yield of this fraction was greatly increased by the grinding. The levels of niacin in the soft flour were not markedly changed by air-classification, with or without grinding, but with the hard flour, relatively high levels were found in the fine fractions. The riboflavin contents of the fine fractions from both flours were relatively high. The pyridoxine levels in the fine fractions were markedly high with the hard, but only slightly high with the soft, flour. With pantothenic acid, while the corresponding rise in levels was marked with the hard flour, it was not shown at all with the soft. These effects may be largely explained on the basis of the thiamine and niacin contents of scutellum, aleurone layer, and endosperm present in the flours. These values, known from previous dissection studies, indicate that the initial flours both contained about 0.05% of scutellum, while the contents of aleurone layer were 0.28% in the hard and only 0.07% in the soft. Grinding the flours with pinned disks caused the scutellum and aleurone fragments to be shattered, so that the proportion present as particles under 17 microns rose from about 10% of the total present in the flour to 55 and 100%, respectively, with the hard flour, and to 40 and 60% with the soft. As a result, the scutellum contents of the fine fractions from the ground soft and hard flours were about 0.8 and 1.2%, and the aleurone contents, 0.2 and 1.4%, respectively. Fiber contents indicated that the aleurone was present in the detached form, free from outer parts of the bran, in the fine fractions. The contents of scutellum and aleurone mentioned account largely for the increased ash content in the fine fractions, the increase being particularly high in the case of the hard flour. They also account very largely for differences in contents of pyridoxine, pantothenic acid, and riboflavin between the fractions of different finenesses, except that, with the soft flour only, protein and riboflavin contents in the endosperm appeared to be directly related.