BLEACHING OF FLOUR. BY E. F. LADD AND H. P. BASSETT. (Received for publication December 15, 1908.) The bleaching of flour or the effect of nitrous acid upon the different constituents of a flour is a subject which has been but little investigated, and is a field which promises to yield interest- ing results where the investigations are pushed along new lines. During the past few years the millers of North Dakota, as well as the rest of the Northwest, if not of the entire country, have been using nitrous acid fumes or nitrogen peroxide produced in different ways for bleaching or “aging of flour.” It seems that no other bleaching agent itself lends so readily to the use for this particular purpose. Nearly all the work done along this line has been the effect on the gluten expansion, volume of loaf, blending of bleached flom with higher grades of flour, etc. With the exception of a paper submitted by Prof. J. H. Shepard, chemist of the South Dakota Experiment Station and Food Commission, nothing has been done to determine the effect of this highly poisonous gas, nitro- gen peroxide, or the acids resulting therefrom on digestion. This, therefore, may be considered the most vital point to be considered because it is here that the deleterious effects, if such there are, will be produced upon man. On certain phases of this question considerable work has been done by Ladd and Stallings and by Professor Alway, whose results are published as Bulletin No. IOZ of the Nebraska Experiment Station. Professor Alway, however, does not seem to have investigated the effects upon the nitrogenous constituents or to have used samples of flour bleached to the extent found upon the market in this state, and he, there- fore, concludes that the use of nitrous acid is harmless since only very small quantities of the reagent are used in the bleaching of flours. by guest on June 9, 2018 http://www.jbc.org/ Downloaded from
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BLEACHING OF FLOUR.
BY E. F. LADD AND H. P. BASSETT.
(Received for publication December 15, 1908.)
The bleaching of flour or the effect of nitrous acid upon the different constituents of a flour is a subject which has been but little investigated, and is a field which promises to yield interest- ing results where the investigations are pushed along new lines.
During the past few years the millers of North Dakota, as well as the rest of the Northwest, if not of the entire country, have been using nitrous acid fumes or nitrogen peroxide produced in different ways for bleaching or “aging of flour.” It seems that no other bleaching agent itself lends so readily to the use for this particular purpose.
Nearly all the work done along this line has been the effect on the gluten expansion, volume of loaf, blending of bleached flom with higher grades of flour, etc. With the exception of a paper submitted by Prof. J. H. Shepard, chemist of the South Dakota Experiment Station and Food Commission, nothing has been done to determine the effect of this highly poisonous gas, nitro- gen peroxide, or the acids resulting therefrom on digestion. This, therefore, may be considered the most vital point to be considered because it is here that the deleterious effects, if such there are, will be produced upon man. On certain phases of this question considerable work has been done by Ladd and Stallings and by Professor Alway, whose results are published as Bulletin No. IOZ of the Nebraska Experiment Station. Professor Alway, however, does not seem to have investigated the effects upon the nitrogenous constituents or to have used samples of flour bleached to the extent found upon the market in this state, and he, there- fore, concludes that the use of nitrous acid is harmless since only very small quantities of the reagent are used in the bleaching of flours.
Experiments with bleached 80~. Our early experiments were to determine the amount of nitrous acid or nitrites present in samples of bleached flour, and after a number of preliminary experiments with methods and samples of flour, a sample of the commercially bleached flour for trade from a North Dakota mill was found to contain:
In 5 grams, 0.0034 milligrams nitrogen. Calculated as sodium nitrite, o. or 67 I. milligrams nitrogen. In flour for one loaf of bread, 373 grams, 1.24656 milligrams nitrogen
as NaNO,. This would be 6.8 parts of nitrogen as nitrite nitrogen per million.
In a sample of the clear, from the same mill, as bleached for trade, there was found :
In flour for I loaf of bread (373 grams), 2.4159 milligrams NaNO,. This would be rz.95 parts of nitrogen as nitrite nitrogen per million.
In a sample of flour taken from a Minnesota mill there was found in the amount for one loaf, 373 grams, 1.313146 milligrams as NaPGO,.
Awzount in bread. A sample of bread, produced. from the flour as commercially bleached from a North Dakota mill, was analyzed to determine the amount of nitrites present, when calculated as sodium nitrite. Three hundred and seventy-three grams pro- duced a loaf weighing, approximately, 18 ounces or 509 grams, and was found to contain 0.44352 milligrams as sodium nitrite, or approximately, one-third of the amount originally found in the flour.
A sample of bread produced in the same way from over- bleached flour, from a North Dakota mill, showed 3.546 milli- grams sodium nitrite, or, slightly less than one-third of that found in the flour.
Effect of bleaching on fat. Fat extracted from the unbleached North Dakota mill flour, that had stood in the laboratory for nine months, gave iodine number (Hanus Mod.) 101.2'. A sample of the same flour, bleached, and which had stood in the laboratory for nine months after bleaching, gave iodine number (Hanus Mod.) 84.1~. Other tests showed similar results. The oil from the bleached sample was more stringy and like the re- sults of the action of the nitrous acid or nitric acid, or thecom- bined action of the same in producing elaiden.
,Vitrogen cwmbiuzed with oil. Two samples of flour, the one bleached and the other unbleached of the same, were extracted with ether. About 200 grams of flour were used, the ether dis- tilled off, leaving the fat, and the residue taken up in redistilled petroleum ether solution, carefully filtered, and the petroleum ether thoroughly evaporated off, thus getting rid of any impuri- ties which may have been originally in the oil from ether extrac tion.
The tests for the presence of combined nitrogen and fat were made as follows:
A piece of well cleaned metallic sodium was strongly heated in an ignition tube and three drops of the wheat flour oil were then allowed to fall upon the partly vaporized sodium. When cool, the contents of the tube were first treated with a little alcohol and then with water. This solution was then filtered, treated with a few drops of sodium hydroxide solution and with ferrous sulfate solution, then boiled for a minute or two. Just enough of dilute hydrochloric acid was added to dissolve the precipitate and, finally, a drop or two of ferric chloride solution was added; the presence of nitrogen being indicated by a precipitate of Prus- sian blue.
Oil from unbleached flour, no nitrogen. Oil from bleached flour, considerable combined nitrogen.
Numerous other tests made upon the oil from bleached and unbleached flour gave similar results.
Tests were next made upon the oil extracted from bread pro- duced from bleached and unbleached flour without the addition of any foreign fat. The loaf was dried, ground to fine meal, extracted with ether, and purified with petroleum ether, as pre- viously described, with results as follows:
Oil from bread, unbleached, no combined nitrogen. Oil from bread, bleached, combined nitrogen.
The amount of nitrogen in the oil from the sample of bread made from the bleached flour was less than in that of the flour from which the bread was produced.
Nitrous and ylitric acid peseuzt. Tests were made showing the presence of both nitrous and nitric acid, or nitrites and nitrates, as reacting material in flour, which had been bleached by the use
of nitrogen dioxide or tetroxide. In many of the experi- ments made, from one-third to one-half of the amount of nitrites found in the flour are recovered in the bread made by the usual process with yeast as a leavening agent. In the case of biscuit, rolls and like products where baking powder or soda is used and in the thinner products, the nitrites are in a large measure de- stroyed by the oxidation to nitrates.
The effect of bleackimg on digestion. In Professor Shepard’s work he investigates the effect of nitrous acid on the action of the digestive enzymes on pure corn starch. This, however, leaves out the action on flour, bread and other products where protein bodies, and in some cases, starch are present, and on this point the following work is reported.
The effect of bleachivzg ox digestiolz of gluteuz and bread: The pepsin solution used in these experiments was prepared accord- ing to the directions given in Simon’s Physiological Chemistry, p. 450, which is as follows:
The following three solutions mere prepared: (A) To 294 cc. of water 6 cc. of hydrochloric acid (1.20 sp. gr. diluted
to JO) was added. (B) In roe cc. of solution (,4) 0.06 gr. of pepsin was dissolved. (C) 90 cc. of solution (A) was brought to 40’ C. in a digestion oven
and IO cc. of solution (B) was then added. These experiments were carried out in the following manner: A test tube three-fourths inch in diameter was cut off forming a short
tube about 33 inches long: in the bottom of this a hole was blown to allow the digestion solution to come in contact with the substance to be digested. In the bottom of this tube was placed a plug of glass wool packed with a glass rod, and on this plu g was placed the gluten or bread to be digested. This was then immersed in the flask containing the digestion solution, and the time noted until the bread or gluten had disappeared. The time could not be accurately determined, but when there was a marked difference, as is shown in some cases, a relative figure could be determined.
Eight trials were made in the manner described using the raw gluten obtained by washing out IO grams of commercially bleached flour by the usual method and treating with zoo cc. of solution (C). The following results were obtained :
In the above cases raw gluten was used, and raw material of this character is much harder to digest than when cooked in some form, so it was thought advisable to try the action of the digestion fluids on baked gluten.
The baked gluten from IO grams of flour was treated in the manner previously described, but no such marked difference could be detected as the digestion was much more rapid and the difference in time could not be noted as well.
Baked gluten from bleached flour was first tried with the fol- lowing results :
In only one case did the baked gluten from unbleached flour require over two hours.
The next trials along this line were carried out on bread made - from each of the flours. The following table gives the results obtained with bread made from bleached flour:
It will be noted that the time of digestion was in favor of the unbleached flour, but the times of digestion are so close that the results are necessarily not as definite as in the case of raw gluten.
Pancreatic digestion. The next problem was to investigate the action of pancreatic digestion on the three different products. The pancreatic solution was prepared for this work according to the directions given by Simon, which are as follows:
To JOO cc. of water 0.28 grams of pancreatin and 1.5 grams of sodium bicarbonate were added. Two hundred cubic centimeters of this solu- tion was used in each experiment.
Four experiments on pancreatic digestion were made, using in each case the raw gluten obtained from IO grams of flour. The following results were obtained:
PANCREATIC DIGESTION OF RAW GLUTEN FROM COMMERCIALLY BLEACHED
It will be noted that in the case of the bleached flour 3 hours or more were required for the complete digestion, while the un- bleached digested in 2 hours or less.
Several tests of each case were made with baked gluten, but the difference, however, could not be so well established as the rate of digestion was so rapid that the difference in time was not as marked as with raw gluten.
By accident a much better test of digestion for the bread was discovered; that of digestion byimeans of the ordinary mold. Some of the bread used in the preceding experiments was allowed to stand in sealed Mason jars, and it was noticed that a large formation of mold appeared on the bread from unbleached flour in four days, while that from the commercially bleached flour remained free from any appreciable amount of mold for nearly ten days. However, the jars containing these samples of bread were not sterilized, and it was thought that this forma- tion of mold might possibly be due to different conditions exist- ing in the different jars. To determine this point the following experiments were carried out, in which we tried to make the con- ditions about the same.
Jars were sterilized in the hot-air oven at I 15” C. and used in experi- ments which were carried out as follows:
First Jar. Bread made from unbleached flour was inoculated with some of the mold on the unbleached bread used in the above experiment.
Second Jar. Bread made from bleached flour was introduced and inoculated with some of the same mold used in no. r.
Third Jar. Bread made from unbleached flour was introduced and inoculated with some of the mold on the bleached bread used in the former experiment.
Fourth Jar. Bread made from bleached flour was introduced and inoculated with the same mold as in no. 3.
The reasons for making these two distinct tests in carrying out these experiments with the mold was due to the appearance of
the mold on the bleached bread, as it seemed to be of a more de- structive nature and it was thought that possibly it might be that it was of a different character. The results from the above experi- ments were as follows:
The bread from the unbleached flour, in both cases, stood in the jars tightly sealed for two days before the mold made any appreciable show. The bread, however, from the commercially bleached flour, in both cases, resisted the action of the mold for five days.
The samples, however, were allowed to stand for IO days and further development noticed. The bread made from unbleached flour, at the end of this time, was almost entirely eaten up; while that from the bleached flour was well covered with the mold, but the texture remained good.
The tests with the mold indicate the same general conclusions as those brought out by the peptic and pancreatic digestions, as they show that the mold digests the bread with a marked difference.
The point might be raised that bleaching was a good thing as it acted as a preservative for the bread, but the pure food law wisely does not allow preservatives of other character, such as sulfites in meats, to be used, and this, no doubt, is similar in character so far as its effect is concerned.
The point was now brought up, if the nitric oxide acted upon the flour, what portions did it act upon-the starch, the gluten, or, only on the fat? To determine this point the fol- lowing observations were made :
If the nitric oxide acted upon the starch it would, no doubt, form a very low nitrated nitro-starch product, and if this were the case, when treated with an acid, and heated up, would give off nitric oxide that would act upon starch, iodide paper, or a solution of starch and potassium iodide; but, when IOO grams of flour were treated in this manner, no such reaction was ob- served, showing, without doubt, that there could not be any action on the starch. However, it was noticed that a large amount of gas was given off, more than could be accounted for by being dissolved in the acid solution or by the expansion of the small amount of air left in the flask. This phenomenon was not noticed when unbleached flour was used.
The next problem now was to determine what this gas was and, as we had no action in the starch, it remained either to be a decomposition product from fat or gluten.
A so-gram sample of bleached flour was then taken and the fat extracted. This fat was then treated in the same manner as the flour, but no such action was noticed; thus, it could only be caused from an action on the gluten, but what this action was remained to be determined.
In studying over the reactions which might occur between such bodies, as the protein bodies, and nitric oxide, we will readily see the possibility of a diazo reaction, and if this occurred the gas should be nitrogen. A Shiff’s azotometer was arranged to collect such gas, and IOO grams of flour were treated in the manner described above. After the complete apparatus had been filled with carbon dioxide to drive out all the air, the acid, which had been previously boiled and was still warm, was intro- duced through a separatory funnel, and the gases formed driven over into the azotometer by more carbon dioxide (the carbon dioxide being absorbed by the potassium hydrate in the azotom- eter) the nitrogen collecting in the top over the potassium hydrate. A very small amount of the nitrogen was given off but enough to be readily measured. This, however, if carried farther, would, no doubt, give means of determining the amount of nitrogen dioxide that actually went into the chemical combi- nation; and, if the flour was over-bleached, the excess could then be approximately determined.
Further evidence to prove this point has recently been secured. In bleaching some flour to the limit to try to duplicate that which collects on the agitators and in other parts of the bleacher, it was also noticed that quite an appreciable heat was developed, indi- cating, no doubt, that a definite chemical reaction was going on. The flour also absorbed the first volume of nitric oxide with extreme readiness. Further, it was noticed that there was a point when this readiness of absorption by the flour was at an end and in order to make the flour further take up more of the gas, vigorous shaking was required and the stream of gas had to be diminished.
This would seem to indicate that the gas acted on the gluten or some part of the gluten until its affinity for the gas was satis-
fied and the further action was either a secondary action on the gluten or that a low nitrated nitro-starch was formed: this point is now under investigation.
The next work relating to this subject was done in the bleach- ing of different flours. A first patent durum flour was bleached with varying amounts of the nitric oxide under the same condi- tions, using 5 cc., IO cc., etc., to the IOO grams of flour. The one bleached with 20 cc., however, was slightly overbleached. This blended with the best white hard wheat flour was used for a standard. The following mixture being made :
Blended. Per cent.
Standard. Per cent.
10 90 Could not be detected by slick. 20 SO <‘ u “ “
40 60 (I <‘ “ ,‘
30 70 “ ‘, ‘I ‘L
It is evident that by the ordinary tests 30 per cent of durum could be introduced without detection. The same thing was tried with flour which was bleached, with IO cc. nitrogen dioxide to IOO grams, with practically the same results.
CONCLUSIONS.
As the result of the experiments given in the preceding pages, and in previous articles, we may summarize the facts in the fol- lowing conclusions :
(I) That nitrous and nitric acid are two of the constituents formed from the bleaching of flour with nitrogen peroxide.
(2) The nitrites and nitrates, or nitrite and nitrate reacting material, are among the products formed in the flour.
(3) That bread as baked in the home by the domestic method will contain from one-third to one-half of the nitrite reacting material found in the flour.
(4) Oil properly extracted and purified from unbleached patent flour contains no nitrogen.
(5) Oil extracted from bleached flour and purified by the same methods gives a strong reaction for nitrogen, thus, con- firming the statement made by Lewkowitsch.
(6) Oils from unbleached flours have an iodine absorption number (Hanus’ method) of IOI or more, while the iodine absorp-
tion number for oils from bleached flours, when properly purified, will have a lower iodine number in proportion to the amount of bleaching.
(7) The difference in the iodine number and the difference in the nitrogen content of the oils show that the bleaching agent has acted upon the fat of the flour.
(8) Flours aged for nine months showed no reduction in iodine number, while the same flour bleached and aged for the same length of time showed a reduction of 17. I points, indi- cating that the artificial bleaching is not the same as the natural aging of flours.
(9) The proportion of nitrates in the bread increases as the nitrites decrease.
(IO) The method of baking will determine to what extent the nitrites are changed or eliminated in the bread.
(I I) Artificial digestion experiments with pepsin solutions showed that the gluten from the unbleached flour was digested in 4 hours and 57 minutes ; while, under the same conditions the gluten from the bleached flour was digested in 8 hours and 40 minutes.
( IZ) The baked gluten from the bleached and unbleached flours showed similar variations but not so wide, the time of digestion being much less ; the same is true for the bread made from such flours.
(13) In pancreatic digestion the glutens digested in 3. I 9 hours from bleached flour, and in 2.31 hours from unbleached flour. The time of digestion in pancreatic solutions of the baked gluten and of the bread was in favor of the unbleached product.
(I 4) The experiments made with the keeping quality of bread made from bleached and unbleached flour demonstrated the antiseptic effect of the bleaching agent.
(IS) It has been demonstrated that there is an action upon the gluten, apparently a diazo reaction. The bleaching agent acted upon the gluten of the flour changing its composition SO that nitrogen gas was given off when the flour was treated with an acid.
(16) The fact that the xanthoproteic reaction takes place demonstrates further that the bleaching agent has acted upon the gluten or protein of the flour.
