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 The intensity of the Kreis test of samples of an oxidized f a t is merit of rancidity has been that have been Proproportional to the amount oj oxygen it has absorbed; or, the amounts confirmed by numerous of 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 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.,
0
1
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
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I N D U S T R I A L A N D ENGINEERING CHEMISTRY
approximately 3 hours, with lard approximately 1.5 hours, etc. Older samples showed shorter induction periods. Samples were withdrawn through the outlet tube at regular intervals and various tests were performed. In order to determine the amounts of fat necessary to give Kreis tests of equal intensity, a small amount of each sample was weighed into a small flask and dissolved in a definite volume of ether. Trial tests were made with varying amounts of each sample until the amounts were ascertained which gave equivalent colors with the Kreis phloroglucinol reagent. Prior to the test the ether contained in each tube was evaporated by placing the tube in a water bath kept a t 40" to 50" C., since it was found that the absence of ether gave more clear-cut results. The volumes of solution of the samples used for each test ranged from 3 cc., with fats but slightly oxidized, to 0.10 cc., or less in the case of highly oxidized fats. The amount of hydrochloric acid used in each case was 1 cc. As a rule the best results were obtained when the amount of fat used in each iegt ranged from 0.10 to 0.50 gram. The iodine liberation test was carried out by ascertaining, in the usual way, the amount of iodine liberated from a slightly acidified potassium iodide solution by 1 gram of fat in 24 hours. The results obtained upon pure butterfat are found in Table I. TABLEI-THE PROPERTIES O F A DRY BUTTERFAT (400 GRAMS)THAT HAS ABSORBED VARIOUSAMOUNTS O F OXYGEN AT 95' c. Iodine Kreis Test Amount Liberated K. from KI in Necessary Acidity Basis 24 Hours for EquivK. N/14 by 1 Gram alent Color Amounts of 100 Oxygen HCl per of Fat Intensities Fat X Vol. Crams Iodine Absorbed 5 G. Fat Oxygen G. No. G. cc. c c. 31.50 . . . . Negative 0.52 0.00 ... ... .... 0.20 31.44 0.88 5.00 4.20 1.05 0,0006 0.014 30.42 0.90 300 4.50 0.0090 1.25 3 0 , SO 0.0010 500 1.05 4.40 1.10 0.0058 0.0017 29.18 1.65 800 4.23 1.06 0,0026 0.00385 28.70 2.00 1100 .
I
.
...
The results shown in this table indicate that in the autoxidation of butterfat there is an increase in the acidity and a decrease in the iodine number. The liberation of iodine from potassium iodide was found to be a slow reaction, but was found to be a comparative measure of oxidations when carried out under similar conditions. The relation of acidity to oxidation will be discussed in another publication. With regard to the tests mentioned, it is evident that neither the iodine number nor the iodine liberation test is sensitive enough to detect small changes through oxidation. The intensity of the Kreis test, however, was found to be very marked with small changes in oxidation. Furthermore, the color intensity i s directly proportional to the amount of oxygen absorbed by a fat; or, the amount of a fat necessary to give equivalent colors with the Kreis reagent i s inversely proportional to the amount of oxygen absorbed, u p to a certain limit. The rigidity of this proportionality is shown by the figures obtained by the products of the oxygen absorbed and the amount necessary to give the chosen color intensity in each case. Where tests are carried out at various times and where a standard with a fat is difficult to maintain, a methyl red standard a t pH 4.8 has been found very convenient for purposes of comparison. Knowing the direct relationship between oxygen absorbed and the Kreis test, it is pdssible to calculate that in the case of a butterfat that has absorbed 1 cc. of oxygen per gram of fat, 11 mg. are necessary to produce such a color intensity. In case of a fat having absorbed 1 cc. per 100 grams, 1.10 grams should give this intensity. The sensitiveness of the Kreis test and its strict quantitative relationship to the oxygen absorbed make it an exceedingly
Vol. 15, No. 10
good measure of the oxygen absorbed, other changes being excluded. Lard contains a high percentage of unsaturated fatty acids, not oleic. Treating a fresh sample of lard under conditions similar to those used in Experiment 1 on butterfat, it was again found, as shown in Table 11, that the intensity of the Kreis test upon samples of oxidized lard was proportional to the amount of oxygen absorbed. It is noted, however, that for equivalent amounts of oxygen absorbed by butterfat and lard per 100 grams of substance the amount of oxidized lard necessary to give a Kreis test of a certain intensity is greater than the amount of oxidized butterfat. TABLE 11-RELATION OF INTENSITY O F KREISTESTTO AMOUNT O F OXYGEN ABSORBED BY 450 GRAMS O F LARDAT 95' Kreiq --___ T- e___d
Oxygen Absorbed cc. 90 180 360 540
Weight of Fat Necessary for uivalent Color intensities G. 1,oo 0.60 0.25 0.075
c.
K. Cc. of Oxygen Absorbed X Weight for Equivalent Color 90.00 108.00 90.00 40.60
K: Bavs of 100 Grams Fat 20.00 24.00 20.00 9.00
According to Lewkowitsch6 approximately 49 per cent of the acids in lard is oleic acid, 10 per cent is linolic acid, and a small fraction is perhaps linoleic. Butter17 on the other hand, contains 36 per cent of its acids as oleic acid, and has no other unsaturated acids, as far as known. It will be shown later that the absorption of oxygen by oleic acid does produce compounds that give the Kreis test in a ratio approximately equal to that of butterfat. In view of this fact the foregoing table for lard would tend to show that the oxygen absorbed by lard in this case was taken up largely by the unsaturated linkages not oleic, and that this absorption does not give rise to compounds which produce a Kreis test. Unfortunately, no linolic or linoleic acid was on hand, so that it could not be definitely determined whether or not oxygen absorption by these acids produces compounds capable of giving a Kreis test. It is extremely important to note here, however, that in no sample used was there more than the slightest trace of rancidity, even after an absorption of 180 cc. of oxygen in 450 grams of lard. If oxidized oleic acid is responsible for the rancid odor in oxidized butterfats, we must assume that in this case unsaturated acids other than oleic are largely involved. The idea that there can be autoxidation without any noticeable rancidity was contrary to all general belief, and for this 'reason various other fats and oils were autoxidized and tested. No quantitative results were obtained upon these oils. Cottonseed oil, which gave practically no Kreis test, when autoxidized gave the Kreis test in increasing intensity but showed only a trace of a characteristic rancid odor. This may explain why sweet cottonseed oil will a t times give a Kreis test. It is possible that oxygen may be absorbed without a proportional formation of compounds that give a rancid odor, but with a formation of those compounds that give the Kreis reaction. Olive oil, which contains practically 93 per cent of its liquid acids as oleic acid, and 7 per cent as linolic, was next tried, with similar results. These results indicate conclusively that for a fat the intensity of the Kreis test is proportional to the oxygen absorbed and is a measure of oxidation, but has no direct quantitative relation to the degree of rancidity as measured by the olfactory senses. That there is no direct quantitative ree "Chemical Technology and Analysis of Oils, Fats, and Waxes," 11, 3rded , p. 780. 7 I b i d , I I , 3rd ed , p 833
October, 1923
INDUSTRIAL A N D ENGl 'NEERING CHEMISTRY
lation may also be shown by absorbing in 110 grams of butterfat 10 cc. of oxygen and comparing this product with 100 grams of butterfat to which have been added 10 grams of butterfat which has absorbed 10 cc. of oxygen. The former will show tallowiness and a Xreis test, while the latter will give a Kreis test of the same intensity but will show little or no tallowy odor, which shows that as oxidation progresses tallowiness and the Kreis test are not developed proportionally. Preliminary tests have shown that mixtures of heptylic aldehyde and pelargonic acid added to fresh fat will produce a condition very similar to tallowiness of butterfat or rancidity of many fats. These compounds and other decomposition products of oxidized fats are undoubtedly the cause of the rancid odors, but neither of the two compounds mentioned above give the Kreis test. As oxidation progreeses, therefore, it seems that the compounds giving the tallowy odors are not formed in stoichiometric ratio to the compounds that give the Kreis test. It is possible that as they are formed they are in some cases subsequently destroyed, or that various unsaturated compounds give different decomposition products. That the oleic acid radical is one constituent that may be concerned in the oxidation and formation of products which give the Kreis test, is shown in the following experiment, where oleic acid was autoxidized. TABLE 111-RELATION O F INTEXSITY O F KREISTESTT O AMOUNT O F OXYGEN ABSORBED BY 300 GRAMSOF OLEIC ACID AT 50° C. (Standard equivalent = pH 4.8 with methyl red) Kreis Test Amount NecesK. sary for EquivWeight of IC. Oxygen alent Color Fat Used X Amount On Basis of 100 Absorbed Intensities of Oxygen Grams of Oleic C C. G. Absorbed Acid 60 0.076 4.56 1.52 90 0,050 4.60 1.50 0,038 4.94 1.63 130 175 0,027 4.72 1.57 475 0.010 4.75 1.58
As in the case of the fats and oils tried, the intensity of the Kreis test is proportional to the oxygen absorbed. Under the conditions under which the experiment was carried out there is no direct ratio between the intensity of the tests with butterfat and lard as compared with their oleic acid content when the unit of oxygen absorbed is the same per gram weight of fat. Two samples of the same fat autoxidized may or may not give equivalent weights for the same intensity of Kreis test when equivalent amounts of oxygen have been absorbed. It has been noted, however, that traces of water present affect the course of the reaction, and it is probable that if all fats tried were absolutely dry when autoxidized a definite ratio would be obtained between the Kreis tests and some one constitutional property of the fats. KerP states that rancidity "can be absolutely prevented 'by the exclusion of oxygen.'' The contention has been made, by a few workers, however, that oxygen is not necessary for the production of rancidity, and this agrees with some further observations that the writers have made. Certain fats when sealed in a vacuum and exposed to sunlight will become rancid and will give a Kreis test. Some fats after prolonged storage without access of light have shown similar properties. It is improbable that the reaction which occurs in vacuo is identical with that which takes place when pure oxygen is absorbed. Properties of the color formed with the Kreis reagent indicate this. Since the change that occurs in a fat that is stored in vacuo without access of light is very slow, and since few fats are subjected to the action of light a t any time in their handling, it is doubtful if any slight action from this cause will have any bearing upon the Kreis test as previously discussed. 8
CotLon Oil Press, 5,45 (1921)
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Detailed experimental work upon the nature of the reaction in fats stored in vacuo in sunlight will be the subject of another publication.
DISCUSSION The experiments upon the oxidation of butterfat and lard reported here were carried out a t 95" C., and consequently the question might be raised whether the reactions a t this temperature would be comparable with reactions occurring a t lower temperatures. Because of the time required for these autoxidation reactions a t lower temperatures, it is not feasible to use these temperatures. Experiments carried out a t 50' C. furnished results that were in good agreement with those reported. Results upon oleic acid at 95" C. agree well with those reported for 50" C. The constants obtained for butterfat, lard, and oleic acid are of no great comparative value as they stand. They serve to indicate, however, that oleic acid will give the Kreis test in proportion to the amount of oxygen that it has absorbed. The results upon lard would indicate that some acid radical or radicals present in this substance will not give the Kreis test when it absorbs oxygen. Assuming that the Kreis test that is produced when lard is oxidized is due to oxidation of the oleic acid radical, we might conclude that oxidation of linolic or linoleic acid radicals produces no compounds that are capable of giving the Kreis test. While the evidence points strongly that way, it can be determined with certainty only when these compounds are subjected to oxidation and the products are tested. I t is significant to note, however, that in all experiments which have been carried out, no case has been noted where there has been appreciable oxidation without giving a Kreis test. This would indicate that, whatever the acid radicals, in addition to oleic, that give rise to the Kreis test, they oxidize simultaneously with other unsaturated radicals that do not give the test. The fundamental nature of the reactions is evidently the same and the autocatalyst for one is also a catalyst for the others. This observation makes it quite certain that the Kreis test is always a good measure of the degree of oxidation where a t least one radical is present which is capable of producing it under such conditions. This is especially true with butterfat, since the oleic acid radical is probably the only unsaturated radical present. In the case of this fat the test has been used with success to follow oxidation changes during storage.
Carbon Tetrachloride Fire Extinguishers According to tests made a t the Pittsburgh Experiment Station of the Bureau of Mines relative to the hazards to fire-fighters from gases and smoke resulting from the application of carbon tetrachloride extinguisher to electric arcs, burning insulation, or fires such as may occur in electrical apparatus and machinery, it was found that the application of 1cubic foot of fire extinguisher to electric arcs and burning insulation in a chamber of 1000 cubic feet capacity developed phosgene, chlorine, and hydrogen chloride in quite dangerous concentrations. Carbon tetrachloride vapors, sulfur dioxide, and carbon monoxide were also formed in less dangerous concentrations. These tests confirm conclusions drawn from previous tests by the Bureau of Mines that it is dangerous to breathe the gases that may be generated from a 1-quart carbon tetrachloride extinguisher applied to a fire in a confined space from which escape is difficult or impossible, and from which the gases would not be removed by ventilation. So far as is known, carbon tetrachloride extinguishers are the most effective and satisfactory of any that can be applied to electrical fires with safety from shock to the operator. Arcs of 60 amperes direct current and 220 volts and 35 amperes and 500 volts were easily extinguished with a I-quart carbon tetrachloride fire extinguisher.
