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INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 15, No. 10
Influence of Starch on Strength of W h e a t Flour’ By J. H. Buchanan and G. G. Naudain IOWA STATECOLLEGE, AMES, IOWA
A
I t has been shown that sizes of starch grains may be measured With this equipment the POSSIBLE relationship between the quickly and accurately by the method described. Tests on seoen sizes of the starch grains typical flour samples indicate a relationship between sizes of grains may be measured quickly starch of wheat flour and accurately. and,flour strength has been and strength of flours. Smaller starch grains tend to indicate a stronger flour. It was found that the suggested by various invesWhether this relationship is due to actual colloidal properties of h ~ c hPains, When extigations. Armstrong2indithe starch or whether it simply reflects the condition under which amined in this manner, cated a variation in sizes of the starch grains of wheat could be grouped in two the constituents were formed, is yet to be determined. flour. Jagoj3 by viscosity classes-those having diammeasurements, showed the eters of 7 microns or less, smaller grains to give greater absorption. With the addi- and those having diameters of 8 microns or more. To show tion of 20 per cent of starch to flour he found the effect upon the accuracy of the measurements Table I is included. It the absorption to depend upon the size of the starch grains. will be noted that only those grains which would be classed The flour, with added rice, showed the greatest absorption, as large are included. wheat second, and potato the lowest. The sizes of the grains TABLEI-DIAMETER OF LARGESTARCHGRAINSI N MICRONS in millimeters were as follows: rice, 0.0060 to 0.0076; wheat, Set 1 Set 2 Set 3 0.002 to 0.052; potato, 0.00 to 0.10. Baking tests indicated 18 14 12 8 22 16 a slight, advantage in favor of the starches having the 24 16 8 12 32 24 smaller starch grains. Hardy4 makes this statement: 24 12 19 10 24 10 16 14 10 12 22 14 16 20 14 18 16
The power of dough to retain its shape may be due, in some cases, primarily to the nature and number of starch grains. Whatever the influence of starch grains may be, they operate as passive agents; the active mechanical properties of dough, its tenacity and ductility, are due to the protein in complex gluten. Snyder6 believed starch to be without effect in influencing the baking strength. The more recent work of Rumseye shows the value of diastatic enzymes in flour. Collatz,? in his study of the effect of addition of diastatic enzymes, arrived a t the conclusion that the starch of strong flour was more easily hydrolyzed than that of weak flour. It is evident that the literature does not give a very definite idea of the importance of starch with regard to strength of flour. Upson and Gortner and Doherty,lo and Sharp and Gortner’l have shown the necessity for a consideration of the colloidal properties of gluten. It was with the idea of determining what the colloidal properties of starch might indicate, with respect to flour, that this problem was undertaken.
EXPERIMENTAL In this work seven typical flours, upon which baking tests had been run in order t o determine loaf volume, were examined for the purpose of determining what influence the size of the starch grains might have. The range of the loaf volumes is given in Table 111. Measurements were made to determine the size of the starch grains in the flours examined. Use was made of a high-power microscope equipped with a micrometer eyepiece. This micrometer was standardized against a Thoma chamber so that each division of the scale corresponded to two microns. Received April 16, 1923 Supplement form. Board of Agrlculture (England), 17, 45 (1910). 8 “Technology of Breadmaking,” p 322 Board of Agriculture (England), 4 Ibrd , p. 319; Supplement form. 1
22 28 16 20 22
24 20 22 36 22 16 16 20 14 14 22 18 22 12 18 14 13 18 12 12 8 12 12
20
30
14
12 16 22
30
.. -
-
TOTAL 505 AVERAGE17.4
561 18.09
20 20 12 28 14 36 26 14 12 8
26 8 12 16 14 18 18 16 10 10 26 20 16 18 20 24 22
-_
544 17.5
I n Tables I1 and I11 are given the data obtained in the examination of the seven samples of flour. Table I1 indicates the percentages of starch grains of different sizes as found in the samples. Table I11 shows the loaf volume, percentage of small grains, and the average size of all the grains in each sample of flour. The sizes are diameters of the grains measured in microns. TABLE11-PER 30 25 t o 20 t o 16 t o 12 t o 8 to
29 24 19 15 11
0 to 8
-
STARCH GRAINSOF DIFFERENT SIZESIN SAMPLE Sample Number---7 15 13 1 6 5 2 11 1.00 0.60 0.90 1.60 1.90 2.20 4.00 0.90 1.00 2.30 1.60 1.90 2.20 2.90 4.50 3.40 6.00 3.90 5.40 9.90 6.90 5.50 5.50 5.00. 5.50 5.80 5.70 6.70 4.00 2.90 2.80 2.90 3.10 1.20 1.30 0.90 0.50 0.50 1.80 2.10 1.00 0.20 83.20 86.10 82.50 82.70 79.80 77.80 78.00
CENT og
Diameter of Starch Grains i n Microns
2
17, 52 (1910) 6 U. S. Dept. Agr., O#ce of E x p t . Sta., Bull 101, 56 6 American Institute of Baking, Bull 8 . Ibzd , Bull 9. 8 J .4m Chem Soc , 37, 1295 (1915) 9 Nebr Agr E x p t S t a , Research Bull 8 . 10 J R g v Research, 13, 389 (1918). 11 J. P h y s Chem , 2 4 , 101 (1920) 7
TABLE111-COMPARISON O F LOAF VOLUME Sample NO.
15 13 1 5 6 2 11
WITH PER CENT O F SMALL GRAINS AND AVERAGESIZE OF ALL GRAINS Loaf P e r cent Average Size of Volume Small All Grains cc. Grains Microns 83.20 6.69 6.76 86.10 7.16 82.50 7.72 82.70 79.80 6.60 77.80 8.21 78.00 9.31
INDUSTRIAL A N D ENGINEERING CHEMISTRY
October, 1923
DISCUSSION An examination of Tables I1 and I11 will show that there '
is a relationship between the sizes of the grains of starch and the strength of flour. With the exception of Sample 15, the flours fall in an order that would indicate that the greater the percentage of small grains the stronger the flour. Sample 13, with a loaf volume of 1640 cc., has 86 per cent small grains. Sample 1 shows a loaf volume of 1540 cc., and 82.50 per cent small grains. Sample 6 shows a volume of 1415 cc. and 79.8 per cent small grains. Sample 11, with a volume of 1265, shows 78.00 per cent small grains. A consideration of loaf volume with the percentage of small grains is not sufficient. By comparing Sample 1 with 6, and 2 with 11, we find very little differences in the percentages of small grains. However, an explanation is offered when we take into consideration the average size of all the grains, and the percentages of grains of different sizes. Sample 1, with a greater loaf volume than Sample 6, shows only 0.6 per cent of grains that are 30 microns or greater in diameter, while Sample 6 has 1.6 per cent of grains of that size.
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Again, Sample 2 shows a greater loaf volume than Sample 11. , If the average sizes of all starch grains are examined, it will be found that the average size of Sample 2 is 8.21 microns, while that of Sample 11 is 9.31 microns. Also, Sample 11 shows 4 per cent of the grains having diameters greater than 30 microns, while Sample 2 has 2.20 per cent. It is believed, then, that the size of the starch grains is a factor in determination of strength of flour, with the smaller grains indicating the stronger flour. I n view of conflicting opinions in the literature with regard to the action of various reagents on starch grains of different sizes, it is not so easy to give a reason for the foregoing conclusion. It may mean that smaller grains indicate a better colloidal condition. The colloidal properties of the gluten have been held by Gortner and DohertylO and others to be an important factor in the determination of strength of flour. It may be that the properties of the starch simply reflect the conditions under which the various constituents of the wheat berry were formed. Further work is now in progress to determine this point.
Quantitative Aspects of t h e Kreis Test' By George E. Holm and George R. Greenbank DAIRYDIVISION,U S. DEPARTMENT OF ADRICULTURB, WASHINGTON, D. C.
F ALL the methods
0
The intensity of the Kreis test of samples of an oxidized f a t is merit of rancidity has been proportional to the amount oj oxygen it has absorbed; or, the amounts confirmed by numerous that have been Proof fat necessary for equivalent color intensities are inversely pro~ o r k e r s .Wagner, Walker, posed for the and Ostermann4 claim, portional to the volumes of oxygen absorbed. tion of rancidity in fats, none has proved of greater The intensity of the Kreis test is not proportional to the rancidity however, that rancidity can be ProducedbY light in value than the PhloroglUcior tallowiness of a fat. A rancid fat will give the Kreis test, but many fats that have absorbed large quantities of oxygen show only the absence of air. nol-hytlrochloric acid test That air, and especially first studied by Kreis. faint traces of rancidity. or none, yet give intense Kreis tests. Some evidence is found to indicate that oleic may be the only unsaturated oxygen, is a factor in the Many objections to the production of rancidity6 of use of this test, have been acid in fats that gives the Kreis test when autoxidized. Absorption of free oxygen is not necessary for the production of fats Or tallowineas in butraised. Wincke12 objected terfat has been shown in the to jt because it is not SPeKreis test by a fat. Exposure of a fat to light without the presence work of the authors. Butcific for aldehydes and keof free oxygen produces a change which causes a Kreis test. terfat exposed to the action tones found in rancid fats, because the depth of color of oxygen will soon lose its produced is not proportional to the degree of rancidity, and color and give simultaneously a strong Kreis test, and will because the test is too delicate. Kerr3 ascribes the failure liberate iodine from potassium iodide in proportion to the of its widespread application to (a) confusion of ideas as to amount of oxygen taken up. These and other tests upon the exactly what is meant by rancidity, and (b) the fact that when product substantiate the views of Winckel and of Vintelesco a fat has become rancid its condition is so clearly evident that and Popesco that peroxides are formed. Oleic acid and no chemical test is needed to recognize it. In his work he triolein acted upon by oxygen give the same characteristic found that (a) all rancid fats give the Kreis test roughly tallowy or rancid odor and the Kreis and iodine liberation but not in proportion to the rancidity, and ( b ) sweet fats tests. These experiments furnished only a qualitative basis do not give the Kreis test-except, in a few cases, cottonseed for comparison of two fats. Fats were therefore studied quanoil. He also agrees with Winckel that the test is too delicate titatively with reference to the amount of oxygen absorbed. and not specific. EXPERIMEXTAL Confusion with regard to the status of the Kreis test has A gastight stirrer was fitted into a flask containing a been due to the fact that those factors concerned in the production of rancidity and those factors involved in produc- weighed amount of fresh, dry butterfat. This flask, coning the test are not well understood. Quantitative data taining an inlet and an outlet tube, was evacuated and filled with oxygen from a gas buret. The flask was kept at a are therefore lacking. Rancidity has been ascribed to an oxidation process, and constant. temperature and the stirrer run a t high speed, the observation that the presence of air favors the develop- and the volume of oxygen absorbed was noted from time to time. The induction period varied with the freshness 1 Presented before t h e Division of Agricultural and Food Chemistry of the sample of fat. With fresh butterfat this period was a t t h e 65th Meeting of t h e American Chemical Society, P\-ew Haven, Conn., April 2 to 7, 1923. 2 2 . Nahr. Genussm., 9, 90 (1905). 3 THISJOURNAL, 10,471 (1918).
Z Nahv Genussm , 26, 704 (1913) T h e term rancidity as used throughout this paper excludes hydrolytic changes in the fats. 4
5
