THE PHYSICO-CHEMICAL PROPERTIES OF STRONG A N D WEAK FLOURS. 111. VISCOSITY AS A MEASURE O F HYDRATION CAPACITY AND THE RELATION OF T H E HYDROGEN ION CONCENTRATION TO IiMBIBITION I N T H E DIFFERENT ACIDS* BY ROSS
AIKEN
GORTNER AND PAUL
FRANCIS
SHARP**
In the earlier papers of this series1’?evidence was presented that strength of gluten is correlated with the colloidal condition of the wheat flour proteins. Mohs3 and later Ostwald.‘ have discussed the problems of bread making from the colloidal viewpoint. Liiers and Ostwald5 studied the viscosity of flour pastes using an Ostwald viscosimeter. The flour pastes were prepared by pouring a suspension of flour-in-water into boiling water thus gelatinizing the starch. They believe that there are two major problems in bread manufacture which should be studied from the standpoint of viscosity. The one has to do with dough formation and the other deals with dough * Presented before the Minnesota section of the American Chemical Society March, 1921, and before the Division of Physical Chemistry of the American Chemical Society at the Fall meeting, New York, N . Y . Sept. 8, 1921. Published with t h e approval of the Director as Paper No. 369, Journal Series, Minnesota Agricultiiral Experiment Station. Abstracted from a portion of a thesis presented by Paul F. Sharp t o the Graduate School of the IJniversity of Minnesota.in partial fulfilment of the requirements for the Degree of Doctor OF Philosophy, June 1922. ** From the Division of Agricultural Biochemistry of the University of Minnesota. R. A. Gortner and E. H . Doherty: Hydration capacity of gluten from “strong” and “weak” flours. Jour. Agr. Research, 13, 389-418 (1918). P. F.Sharp and R . A . Gortner: Physico-chemical studies of strong and weak flours. 11. The imbibitional properties of glutens from strong and weak Pours. Jour. Phys. Chem., 26, 101-138 11922). K. Mohs: Zeit. ges. Getreidew.. 7, 238-212, 250-260 (1915). W. Ostwald: Kolloid-Zeit., 25, 28-45 (1919). Liiers and W. Ostwald: Kolloid-Zeit., 2 5 , 82-90, 116-136 (1919).
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482
baking. These authors believe that the properties making for a good dough and those making for good baking conditions are distinct. I n an investigation of the different grades of flour they found that the viscosity of flour pastes divided themselves into three classes: the patent flours showed a greater viscosity than did the straight flours, while the clear flours showed the least viscosity. This was found t o be true for both wheat and rye flours. They concluded that the viscosity of flour pastes was directly proportional to the starch content and suggested that the viscosity of flour pastes be used as a method for the determination of the starch content of flours. The addition of various amounts of sulfuric acid was found to have little effect on the viscosity of flour pastes. Suspensions of flour-in-water without heating were investigated, the flour concentrations ranging from 7 to 20 percent. It was found that rye flours of the same grade and concentrations gave relatively much more viscous solutions than did wheat flours, and the authors suggested this as a method of differentiating between the two. I n the case of the wheat flour suspension, the lower the grade of the flour the more viscous was the solution. This is just the reverse of the behavior of the flour pastes prepared by heating the flour-in-water suspension so as to gelatinize the starch. Lactic acid was found to markedly increase the viscosity of (unheated) wheat flour suspensions, the effect being more pronounced the higher the grade of the flour. Lactic acid seemed to have no effect in increasing the viscosity of rye flour suspensions. Luers6 studied the effect of acids, bases and salts on solutions of gliadin prepared from wheat and rye flours. With acids the maximum viscosity was attained at 0.0004 to 0.00066 normal hydrochloric acid, with 0.0022 normal sulfuric acid, and with 0.018 to 0.0011 normal lactic acid. With alkali the maximum viscosity was reached a t 0.0022 normal sodium hydroxide, and at 0.013 to 0.014 normal barium hydroxide. 6
H.Liiers: Kolloid-Zeit., 25, 177-196, 230-240 (1919).
Physico-Chemical Properties of
Flours. 111
483
Hydrochloric acid was found to increase the viscosity of gliadin dissolved in alcohol. I n all of the experiments reported, no essential difference was noted between the gliadin from wheat and rye and the author concluded that they are identical. This confirms the earlier conclusions of Griih and Friedl.' Liiers and Ostwald8 studied the viscosity of suspensions of two poor rye flours and found that both gave low viscosity values one having only about one fourth the viscosity of normal rye flour of the same grade. They emphasized that the best flour would probably show an optimum viscosity, neither too high nor too low. Liiers and Ostwaldg discuss the work of Upson and CalvinlO,ll on the colloidal swelling of wheat gluten and state that their own conclusions are in essential agreement. While both emphasize that it is the quality and not the quantity of gluten which is important, nevertheless they seem to believe that the quality of the gluten is regulated by the acids and salts present in the flour or added to it in the bread making process. They make no reference to the work by Gortner and Dohertyl? who have shown that the conclusions of Upson and Calvin were based upon insufficient evidence. Luers and Schneider13 concluded that the three methods of measuring imbibition as effected by acids, namely the increase in weight of discs, the viscosity method, and the sedimentation method, all lead to the same relative results. Sharp and Gortnerl' found that drying the washed gluten in a vacuum oven at 45" to 50" C markedly altered the physico-chemical properties of the glutens, the properties of the 7
J. Groh and G. Friedl: Biochem. Zeit., 66, 154-164 (1914).
H. Luers and W. Ostwald: Kolloid-Zeit., 26, 66-67 (1920). H. Luers and W. Ostwald: Kolloid-Zeit., 27, 34-37 (1920). l o F. W. Upson and J. W. Calvin: Jour. Am. Chem. SOC.,37, 1295-1304 (1915). l 1 F. W. Upson and J. W. Calvin: The colloidal swelling of wheat gluten in relation to milling and baking. Nebr. Agric: Exp. Sta. Res. Bull., No. 8, 27 pp. (1916). Gortner and Doherty: LOC.cit. l 3 H. Liiers and M. Schneider: Kolloid-Zeit., 28, 1-4 (1921). l4 P. F. Sharp and R. A . Gortner: Loc. cit.
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484
R. A. Gortner and P. F. Sharp
different glutens becoming more nearly alike. I n the same paper data were presented indicating that the optimum hydrogen ion concentration for the imbibition of discs of gluten was the same for the various acids. We concluded that our findings were in complete accord with the earlier postulate of Gortner and Doherty,12 i. e., “The difference between a strong and weak gluten is apparently that between a nearly perfect colloidal gel with highly pronounced physico-chemical properties, such as pertain to emulsoids, and that of a colloidal gel in which these properties are much less marked.” In continuing the investigation of the colloidal properties of wheat flours, the viscosity of flour-in-water suspensions was studied to determine its suitability as a method for the determination of the imbibitional powers of the flour proteins as affected by acids. The viscosity method of measuring imbibition offers distinct advantages over the increase-in-weight-of-discs method. The viscosity method is more rapid, results are reproducible within a smaller experimental error, less material is required, and the inconvenience of washing out the gluten is avoided. Liiers and Ostwald appear to conclude that the greatest baking strength of flour is associated with a medium viscosity of simple flour-water suspensions. Our finding is that the strength of the flour is not so much related to the original viscosity of the simple flour-water suspension as i t is to the change in viscosity effected by treating such a suspension, with an acid or alkali, that is, to the imbibitional power of the protein as influenced by acids or alkalis. If i t were true that the greatest baking strength is associated with a high viscosity of a simple flour-water suspension then we should expect rye flours to have markedly greater baking strength than wheat flours, for according to the data of Luers and Ostwald, rye flours yield suspensions which are much more viscous than are wheat flour suspensions of the same concentration. On the other hand if the flours which yield simple flour-water suspensions of medium viscosity are the strongest (this is the belief of Liiers and Ostwald) then we should expect the weak
Physico-Chemical Properties o j Flours I I I .
435
rye flours cited by Luers and Ostwald, to have the greatest baking strength inasmuch as they show viscosity values intermediate between those of their strong rye flours and the wheat flours. If, on the other hand, the baking strength of a flour is associated more or less with the increase in viscosity produced by acids, then we would expect rye flour to be an ex. tremely weak flour as compared with wheat flour, for, according to the work of Luers and Ostwald, the imbibitional powers of rye flour are not increased by treatment with acid while the imbibitional powers of the wheat flours increased markedly. The weakness of the rye flours cited b y Luers and Ostwald may be due to a low protein content, this supposition cannot be verified from their published work for no protein deterrninations were given. We have pointed out in the preceding paper14 that weakness of flour may be divided into three classes, (1) weakness due to an adequate quantity of gluten but of inferior quality, (2) weakness due to an inadequate quantity of gluten of good quality, and (3) weakness due to factors influencing yeast activity, diastatic and proteolytic enzymes, hydrogen ion concentration, etc. It is believed that the first two types of weakness are the ones most frequently met with although the data by Rumsey15 indicates that the soft wheats may also be low in diastase. The work of Pauli and HandovskylG,H a n d o v ~ k y ' ~ Fischer' and others indicates that the various acids influence the imbibition of proteins to markedly different degrees. LoebIg advanced the claim, supported by his experiments with gelatin, casein and albumin, that maximum imbibition occurs with all acids at the same hydrogen ion concentration and that the same high point is reached regardless of the acid used. Sulfuric acid, because of its ability to function as a dibasic acid l5 L. A. Rumsey: The diastatic enzymes of wheat flour and their relation to flour strength. Amer. Inst. Baking, Bull. 8, 86 pp. (1922). I 6 W. Pauli and H. Handovsky: Biochem. Zeit., 18, 340-371 (1909). l7 H . Handovsky: Kolloid-Zeit., 7, 183-193, 267-277 (1910). . M. H. Fischer: Oedema and Nephritis; 2nd Ed. (1915). lD J. Loeb: Proteins and the theory of colloidal behavior, 292 pp. 80 figs. (1922).
R. A. Gortner an.d P. F . Sharp
486
a t the hydrogen ion concentration of maximum imbibition, produced only about half the effect of a monobasic acid. Gortner and Doherty, and Sharp and Gortner found that different acids did not produce the same maximum imbibition of gluten discs but the later authors did conclude that the maximum imbibition of discs produced by various acids occurred at practically the same hydrogen ion concentration. The investigation here reported was undertaken to further investigate this point, and to ascertain which acid would be the best suited for the measurement of the imbibitional capacity of flours by the viscosity method.
Experimental I n this work no attempt has been made to distinguish between viscosity and plasticity, nor to determine the plasticity constants for those mixtures which were undoubtedly plastic. The term viscosity has been used in a rather loose sense throughout, to indicate all resistance offered by the suspensions to the shearing force applied. I n this investigation we worked with the same flours used in the previous Flour B-780 was taken as an example of a strong flour and flour B-783 as an example of a weak flour. Flour analyses and baking tests of these flours were reported in Tables I and I1 of the preceding paper20 and will not be repeated here. We need only mention that the crude protein (N. X 5.7) in these flours is almost identical (B-780 = 12.13%: B-783 = 12.15%) ; ash values are fairly low (B-780 = 0.4470 B-783 = 0.5370). The value of such an extended investigation on the same flours might be questioned due t o the fact that flours are known to-change in baking strength with age. It is believed, however, that the effect of age did not exert an appreciable influence on the results of this investigation. The flours were stored at ordinary room temperature for about six months 2o
P. F. Sharp and R. A. Gortner: LOC.cit.
Physico-Chemical Properties of Flours. 111
487
before the investigation was started, from then on they were stored in air tight containers in a cold storage plant a t a temperature of about 3" C. The imbibitional power of the gluten was determined by the increase in weight of discs both at the beginning and a t the end of the investigation and no difference in the imbibitional power of the gluten could be detected by , this method after the flours had been kept in storage for two years. Preliminary determinations were first carried out with 20 percent flour-in-water suspensions using an Ostwald viscosimeter according to the method advocated by Liiers and Ostwald. Several difficulties were encountered and the method was finally abandoned. Successive readings with the same flour-in-water suspension gradually decreased. Difficulty was encountered in preparing duplicate suspensions which would have the same viscosity values. The time of outflow through the capillary tubes became for some flours excessively long. After accumulating considerable data by this method it was finally abandoned for a viscosimeter of the torsion wire type. The data from which we have drawn our conclusions were all obtained with a MacMichaelZ1viscosimeter of the original type. A very definite experimental procedure was adopted and rigorously adhered t o ; by so doing duplicate results could be obtained which agreed within a small experimental error. The moisture in the flour was determined, and enough flour taken to make 25 grams on the dry basis, to this amount of flour sufficient water was added to make a total of 100 grams of water counting that already in the flour. The mixture was allowed to stand for one hour with occasional shaking. All determinations were carried out in a room electrically controlled where the temperature was maintained at approximately 25" C. The viscosity of 100 cc of the mixture was first determined and then normal solutions of the various acids were added in gradually increasing amounts up to 10.0 cc of the normal acid. Quadruplicate readings were taken after each 21
R. F. MacMichael: Jour. Ind. Eng. Chem., 7, 961-963 (1915).
4YS
K . .4.Gorlizer
aid
P . F . Sharp
addition. The effect on the viscosity of diluting mixtures of various viscosities was determined and from the results so ohtained the viscosities were corrected for dilution by the assumption of a linear interpolation. The effect on the viscosity of the addition of the following total amounts of a normal acid
Fig. 1
Viscoqity of 100 cc of 207, flour-in-water suspensions of strong flour B-780 as affected by different amounts of various acids.
solution was determined: 0.10, 0.20, 0.30, 0.40, 0.30, O.GO, 0.70, 0.80, 0.90, 1.00, 1.20, 1.50, 2.00, 2.50, 3.00, 4.00, -5.00, 6.00, 8.00, and 10.00 cc. The readings are all expressed in degrees MacMichael (MO) and are comparable only among themselves. Any resetting of the wire in the viscosimeter
was found to displace the readings for the flour mixtures one way or the other, although the viscosimeter showed exactly the same reading with a standard sucrose solution. The values obtained are probably a combination of the effects which go to make up both viscosity and plasticity. For these reasons the attempt to express the results in the terms of absolute viscosity units would be of doubtful value. The speed of the motor was adjusted so that, with the wire used in this work, a sucrose solution, whose absolute viscosity was 5.73 centipose, gave a reading of 14.3 degrees MacMichael.
140
100
60
20 0
2
4 6 CCS. NORMAL ACID
a
Fig. 2 Vi5co:ity of 100 cc of 20yc flour-in-water suspensions of weak flour B-783 as affected by different amounts of various acids.
The results obtained with flour B-780 are expressed graphically in Figure 1 and those with flour B-783 in Figure 2. I t will be noted that the same maximum is not reached with the different acids and that if the acids are arranged in the order of their ability t o produce maximum imbibition this order is not the same with the two flours. Meta-phosphoric acid produces no increased imbibition with either flour, while sulfuric acid produces increased imbibition with flour B-780 but not with flour B-783.
490
R. A. Gortvler and P . F . Sharp
The hydrogen ion concentration was determined electrometrically on 20 cc aliquots of the flour-in-water suspension t o which had been added the proportionate amount of acid t o correspond with the various points on the imbibition curve. The imbibitional data plotted against the p H of the flour-inwater mixture are expressed graphically in Figures 3 and 4. The curves in these last two figures are all similar in shape and
Fig. 3 Viscosity of 100 cc of a ,207, flour-in-water suspension of strong flour B-780 a t different hydrogen ion concentrations produced b y various acids.
all tend t o reach a maximum in the neighborhood of a pH of 3.0 which agrees with our earlier conclusion in regard to the swelling of gluten discs. The curves shown in Figures 3 and 4 do not all reach the same maximum viscosity. A flour-inwater suspension is a complex colloidal system and it is perhaps not surprising that a relationship which 1,oeb found to hold
Physico-Chemical ProFerties of Flours. 111
491
for a highly purified and perhaps altered protein material does not hold in such a mixture. From the shape of the curve it can be seen that lactic acid effects the least change in viscosity per unit of actual acid concentration and is therefore probably best suited for the
Fig. 4 Viscosity of 100 cc of a 20% flour-in-water suspension of weak flour B-783 a t different hydrogen ion concentrations produced by various acids.
measurement of the imbibitional capacity by the viscosity method. This agrees with the results of Gortner and Doherty using the increase in weight of discs as a method of measuring the imbibitional capacity of the gluten.
Summary 1. The viscosity method offers a rapid and easily duplicable method for the measurement of the relative imbibitional capacity of the gluten colloids of flours. It is far superior to the method of weighing gluten discs. 2. Our earlier observations that there are marked differences in the imbibitional capacity of the gluten colloids from strong and weak flours are confirmed. 3. The same maximum viscosity is not reached when mixtures of flour and water are treated with various amounts of different acids.
492
R. A. Gortiasr avld P. F . Sharp
-4. The order of the acids arranged according to their ability to produce maximum imbibition is different with the two flours. This indicates a different Hofmeister series for each flour. 5. The hydrogen ion concentration at which the various acids produce their maximum imbibition is approximately the same, and is roughly at a pH of 3.0 (C, X lo+).
NEW BOOKS The Examination of Hydrocarbon Oils and of Saponifiable Fats and Waxes. B y D . Holde. Translated by Edward Mueller. Second edition. 23 X 15 cm; p p . nrix 572. New Fork and London: John Wiley and Sons, Chapman and Hall, 1922. Price: $6.00.-The second English edition is based on the fifth German edition. There are nine chapters: general methods of examination; petroleum and petroleum products; natural asphalt; ozocerite; hydrocarbons (tar) obtained by distillation of coal, shale, resins, and wood; vegetable and animal fats and oils; industrial products prepared from fats; waxes; physicochemical tables. The question of static electricity comes up on p. 122. “When woolen fabrics are agitated in ether or in naphtha a n electrical excitation results. Richter has shown that in each case the exciting liquid (ether or naphtha) assumes a negative charge; the woolen material becomes charged positively. These charges may reach such a value that sparks may result if a workman approaches or touches the material with his hand, and if the proper air and combustible vapor mixture is present, a serious fire may be started. Conflagrations in chemical cleansing establishments have been due t o such sparks. Richter proved that such fires might be prevented by dissolving in the naphtha a small amount (as little as onetwentieth of one percent) of magnesium oleate. However, the action of this material was not understood. “Richter showed that fires might also result from sparks due to charges generated by the frictional flow of inflammable liquids (ether or naphtha) through narrow pipes either under their own pressure or that of a force pump. In this case also he suggested a practical solution of the difficulty. H e found that sparks did not form if the liquids were run through non-conducting earthenware or glass funnels instead of metal funnels, or if a metal funnel seemed t o be necessary all trouble was avoided by having a metal chain attached which could make good electrical connection with the earth. If metal funnels were used without earthing electrical charges might build up, and, on the approach of a workman, a spark might pass with disastrous results.” On p. 165 we read that “the use of oils to lay the dust on streets depends on the very slow evaporation of the heavier components, on the ease of oxidation to asphaltic bodies, and on the disinfecting action of the tar and tar oils. The tar applied hot, is brushed into the street or an emulsion of oil and water is used. The materials best suited for laying the dust are crude oils, heavy asphaltic oils, oil residues, tars, liquid asphalts, or a mixture of tar and clay. “ I n printing establishments and type foandries, the floors are oiled regularly, since after one treatment with non-drying oil they can be swept without raising the dust. In some respects this is not satisfactory, because the floors become slippery and are thus likely to lead to injury. . . .For oiling wood floors pure mineral oil should be used t o prevent rancidity, and to avoid slipperiness an oil of specific viscosity 30 to 40 at 20’ is advisable. The oil should not get sticky after several weeks. Krist thinks that floor oils should be pure mineral
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