428 



SCIENCE 



[N. S. Vol. L. No. 1297 



cussion of recent digestion experiments on 

 bran either by Holmes^ or Snyder.^ 



It is a matter of regret that Holmes did not 

 make, or at least did not publish, the proxi- 

 mate analysis of the bran used in his 

 digestion experiments. The bran is merely 

 described as " an ordinary commercial wheat 

 bran secured in the open market." 



For the purpose of this study then we may 

 divide the wheat berry into three portions : 

 The germ or embryo, the branny covering 

 and the flour cells. The branny covering in- 

 cludes several outer and middle layers and the 

 inner layer termed the aleurone layer. The 

 aleurone layer or so-called gluten cells con- 

 tains proteins apparently in higher amount 

 than the outer layers, but the gluten cells do 

 not possess the properties of, nor take part in 

 the formation of gluten. Hence, although 

 functionally the aleurone layer is a part of 

 the endosperm and serves as a covering for 

 the flour cells or so-called starch cells or floury 

 portion, actually the physical property it 

 possesses of close adherence to the outer coat- 

 ings during the milling process, obliges us 

 to consider it as simply one of the bran 

 layers. iNTeither the bran coats nor the germ 

 contains starch grains or those protein bodies 

 which possess the same characteristics as the 

 crude gluten obtained from the flour cells by 

 the customary mechanical method of washing 

 away the starch from a flour dough. Never- 

 theless commercial bran as obtained from all 

 processes of milling at present employed con- 

 tains considerable amounts of starch and 

 gluten. The germ is, for the most part, 

 recovered in the shorts or sometimes as a 

 separate fairly pure product sold as " germ 

 middl ings." "Bran manufactured by large well- 

 equipped mills making use of the most im- 

 proved bran dusting machinery is less " rich " 

 than bran made by the average mill of smaller 

 capacity. In other words, when the bran is 

 closel.y " skinned " it contains less flour than 

 " rich " bran. The flour present in bran 



1 "Experiments on the Digestibility of Wheat 

 Bran in a Diet without Wheat Flour," TJ. S. De- 

 partment of Agriculture. Bulletin No. 751. 



2 Science, N. S., 50, August 8, 1919, pp. 130- 

 132. 



exists both as loosely adhering but separate 

 particles and unseparated masses of flour 

 cells. ISTo system of milling, however perfect, 

 is at the present time capable of removing 

 all the floury portions from the bran. Bran 

 contains easily visible specks of flour, both 

 free and adherent. Sometimes millers test 

 the clean-up of their bran by rubbing it upon 

 the coat sleeve or other piece of dark colored 

 cloth. Commercial shorts contains still larger 

 amounts of flour particles. White middlings, 

 "red dog" and other "rich" feeds contain 

 still more. 



One of the tests which the cereal testing 

 laboratory is frequently called upon to per- 

 form is the determination of the amount of 

 flour present in bran, shorts and other by- 

 products of flour milling. The method which 

 we have generally used for this purpose is to 

 determine the percentage of starch. On ac- 

 count of the presence in bran of considerable 

 amounts of pentosans and other carbohy- 

 drates, the usual Sacchse method for starch 

 determination is not applicable. The diastase 

 method^ is usually used for this purpose. 

 Since wheat flour contains on the average 

 about 70 per cent, of starch, the amount of 

 floury material or potential flour present in a 

 wheat by-product may be determined with a 

 fair degree of accuracy by determining the 

 amount of starch and multiplying by one 

 hundred seventieths. Very few samples of 

 bran have as low as 12 per cent, of floiu-. The 

 average of some recent analyses of com- 

 mercial brans gave 18.93 per cent, floury 

 material. These may possibly not be repre- 

 sentative, but the average amount of floury 

 material in commercial bran will not be far 

 from 15 per cent, and 30 per cent, floury 

 material in commercial shorts is perhaps an 

 average amount. 



Consideration of the amounts of flour in 

 average commercial bran will throw a little 

 further light upon the subject of the digest- 

 ibility of the branny coatings in the human 

 stomach. Bearing in mind then the per- 

 centages of digestibility found by Holmes 



s TJ. S. Dept. of Agriculture, Bureau of Chemis- 

 try, Bulletin 107, p. 53. 



