THE J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y . found by four for the actual per cent. of oil in the meats. The use of a wire gauze strainer was unnecessary with meats.
DETERMINATION OF SULPHUROUS ACID OR SULPHITES OR SULPHUR DIOXIDE IN FOOD PRODUCTS.’
TABLE12. PER CENT. OF OIL Temperature. Time. 70’ 5 70’ 15 70’ 30 60’ 15
IN
81
BY EDWARD GUDEMAN.
UNCOOKED MEATS.
I.
Received October 27, 1908.
11.
The method for the determination of sulphurous acid or sulphites or sulphur dioxide in food products ... ... as given in the Official and Provisional Methods 107, revised, Bureau From these results it is evident that the standard of Analysis, Bulletin time and temperature of extraction of meal is of Chemistry, Dept. of Agriculture, having been suited also for extraction of the one-fourth quan- accepted by the Association, is the standard or tity of meats. Experiments using a larger propor- official method of analysis. tion of meats showed low results. Whether this The essential part of the method calls for a direct was due to incomplete extraction or to a possible distillation of IOO grams of ’the food product (with change of the specific gravity curve for such high or without addition of water) acidified with 5 cc. per cents. was not determined. of 2 0 per cent. glacial phosphoric acid, distilling into an excess of a standard iodine solution and TABLE13. PER CENT. O F OIL I N COOKED MEATS. titrating back the excess of iodine ; the distillaTemperation is considered complete when 50 cc. have disture. 5 min. 10 min. 15 min. , tilled over. In the analysis of meats and meat I. 11. I. 11. I. 11. products the phosphoric acid is increased t o 2 0 50” 29.84 ... 29.72 ... 29.60 29.72 ... 29.88 ... 30.34 ... 60’ 29.60 cc. (page I I ~ ) , and in the examination of wines, 70’ 29.40 29.88 30.22 30.76 ...... direct titration of the sulphurous acid, without Again the extraction a t 60° for 15 minutes is distillation, is permissible (page 188). sufficient . A large number of analyses of natural and preThat the presence of moisture does not affect pared food products have shown that often weighthe extraction was demonstrated by extractions able amounts of sulphur dioxide (or its compounds) on both raw and cooked meats, a t 6 o o C . , for 15 will be obtained from food products that actually minutes, thus : contain none a t all, and when sulphur dioxide TABLE14. is present, the amount obtained by the official RAWMEATS (moisture 8.95): I. 11. method will be in excess of the amount actually Hydrous. ................. 29.28 ... present, using the official method without modiAnhydrous................ 29.40 29.12 fication. Many animal and vegetable food prodCOOKEDMEATS (moisture 5.73): I. 11. ucts normally contain sulphur compounds, which Hydrous .................. 30.84 ... on distillation with acids give off volatile sulphur Anhydrous................ 31.40 31.00 Hulls.-After transferring 40 grams of hulls compounds, which react with the iodine solution t o the Erlenmeyer flask it was found necessary and reducing the excess of standard iodine soluto pack the hulls with a glass rod in order to insure tion used, are thereby calculated to and considcomplete covering with IOO cc. of carbon tetra- ered and reported as sulphur dioxide present in chloride. No wire gauze strainer was necessary the food product examined. Recognition of this source of error is taken when applying the method in filtering the extract. t o the examination of meat and meat products, TABLE15. Time. Per cent. of oil. it being stated “mere traces should be ignored” (page 113). A like statement should be added Temperature. Min. Soxhlet extraction. Sp. gr. method. 60 5 0.30 0.25 to the official method itself, applying in the ex60’ 10 .. 0.32 amination of all food products, ignoring the pres60 15 .. 0.25 60 30 .. 0.25 ence of “mere traces” of sulphur dioxide. It is proposed to extend the investigation t o Sulphuretted hydrogen often liberated by the the determination of oil in linseed products, and action of the acid, will react on the iodine solution of fats in feedstuffs, tankage, etc. and be reported t o that extent as sulphur dioxide, 27.12 29.12 29.44 29.28
27.40 29.28
&
7
c _ .
c
UNIVERSITYOF NORTHCAROLINA, CHAPEL HILL, N. C.. OCTOBER29, 1908.
7 -
7
Read before the Association of Official Agricultural Chemists,
Nov., 1908.
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY.
82
unless the sulphides are ’separated by first passing the distillate through some solution of a metallic salt, as recommended by W. D. Horne and A. I,. Winton. I n many cases the sulphides can be held back by adding some metallic salt (cadmium, copper, silver, lead, etc.) directly to the product before beginning the distillation, thereby simplifying the process and not requiring the additional apparatus. Volatile sulphur compounds which do not +appear as sulphuretted hydrogen and are not held back by the metallic salts, will react on the iodine solution and be calculated to and reported as sulphur dioxide present in the food product, and such volatile sulphur compounds will erroneously increase the amount of sulphur dioxide, free or combined, actually contained in the product. In the direct distillation of an acidified food product a high temperature of distillation is caused by the food product itself. During the direct distillation, concentration of the mass takes place and the acidity increases in nearly direct proportion to this concentration. With food products to which no water need be added for distillation, the original acidity (due t o the added phosphoric acid) is I to 4 per cent. based on the product used (100 grams), and after distillation taking off 50 cc., the acidity will be nearly double z to 8 per cent., decomposition of the product increasing with the increasing acidity, giving rise to the peculiar volatile sulphur compounds. The decomposition of the food product due to the concentration, with increased acidity and high temperature, is often intensified by the previous treatment such prepared food product undergoes during its method of preparation, the “processing” of the product, especially noticeable with canned goods, which have been cooked or sterilized at high temperature. The analytical figures show that some fresh products, containing only traces or no sulphur dioxide in the raw state, after processing give strong reaction for sulphur compounds (see table). It was often found that a distillate of 50 cc. from a Ioo-gram sample was not sufficient to carry over all the sulphur dioxide and the other volatile sulphur compounds. Accidentally correct results may be obtained for sulphur dioxide, the distilled volatile sulphur compounds counterbalancing the loss of sulphur dioxide due to incomplete distillation, especially with such products that on heating become thick and gelatinous, Reports by W. D. Bigelow. F. Zerban and W. P. Naquin, Proceedings A . 0.A . C.. Bull. 118, Bureau of Chemistry, issued Oct. 27. 1
1908.
causing foaming and bumping. Increasing the amount of the distillate produces greater decomposition, especially noticeable with food products, to which no water need be added for distillation, such as fruit juices, cordials, extracts, wine, beer, etc., all of which contain not over 2 0 per cent. non-volatile matter. The following simple modification of the official method has been found to eliminate many of these sources of error and to overcome most of the other objections raised. Instead of a direct distillation, the volatile products are driven over with low pressure steam. The steam is generated from distilled water and directly led into the mass. A good Bunsen burner will generate enough steam to make from 6 to 8 distillations at one time, within one hour, giving 4 t o 500 cc. of distillate per sample. Any of the well-known water stills can be used, replacing the condensing coil with a copper tube, having sufficient stop-cock openings from which the steam is led through rubber tubing, into the retorts or distilling flasks containing the products to be analyzed. The accompanying sketch is self-explanatory.
n
On account of condensation of steam during distillation, no possible concentration can take place, in fact dilution takes place and the retort or other distilling flask must be sufficiently large to accommodate this increase in bulk. Excessive condensation can be overcome by increasing the steam pressure or by using a small burner under the sand bath on which the distilling flask rests. The temperature of distillation can never increase above that of the steam used. Acidity cannot increase, in fact the acidity will decrease in nearly 1 Cwtinous water stills can be used if feed water is free from volatile sulphur compounds. Complete apparatus can be obtained from E. H. Sargent & Co., Chicago, to whom my thanks are due for the above illustration.
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y . exact proportion as dilution takes place, due t o the condensation on the sides 'of the retort. The steam entering below the surface of the mass acts as a mechanical stirrer and prevents foaming and bumping. Decomposition of the mass due to concentration, high temperature and increased acidity are eliminated and the distillate contains no volatile sulphur compounds due to such decomposition as found in the method with direct distillation. Using steam the amount of the distillate can be regulated and always can be sufficiently large (3-500 cc.) and of such character, that the sulphur dioxide can be determined by direct titration with iodine solution, as per method z , page 168, Bull 107, revised, thereby doing away with any error due to loss of iodine. For such direct titration of the distillate the method is modified by replacing the iodine in the absorption tube, beaker or flask, by a weak alkaline solution, a large beaker being most convenient. When distillation is complete, the starch indicator is added, distillate slightly acidified with hydrochloric, sulphuric or phosphoric acid and quickly titrated with a standard iodine solution. The use of steam for distillation was found to have extended application, especially in the determination of sulphurous acid and its compounds and in the examination and determination of glycerin, ammonia, volatile fatty acids, alcoholic beverages, ether, aldehydes, extracts, turpentine, cereals, etc. and in obtaining distillates from substances that foam or bump. Some comparative results in the determination of sulphur dioxide in food products are as follows: SULPHURDIOXIDEFOUND. Parts per 100. Official method. Modified method.
83
SULPHUR DIOXIDEFOUND. Parts per 100. Official method. Modified method.
. ---
Direct ti- After Direct ti- After tration. oxidation. tration. oxidation. Prepared samples. Candy 0.0120 0.0120 0.0126 0.0126 Peas,fresh,average5 0,0002 0.0002 0.0000 0.0000 Peas, same processed.. 0,0002 0.0008 0.0000 0 .OOOO 0.0003 0.0008 0.0000 0.0002 Peas,canned,average S . . . . . Peas,canned,average5 0.0004 0.0011 0.0002 0.0004 String beans, white, fresh 0.0000 0.0003 0 .OOOO 0 .OOOO String beans, same processed.. 0.0002 0.0007 0,0000 0,0002 0.0001 0.0002 0 .OOOO 0,0000 String beans, yellow, fresh.. String beans, same processed.. 0.0001 0.0005 0 .OOOO 0.0002 0.0002 0.0003 0 .OOOO 0.0000 Cabbage, fresh.. Cabbage, same processed.. 0.0002 0.001 1 0,0000 0.0003 Green peppers, fresh. 0.0000 0.0002 0 .OOOO 0.0002 0.0002 0.0006 0,0000 0.0003 Green peppers, same processed. Cauliflower,fresh 0.0000 0.0000 0.0000 0.0000 Cauliflower, same processed.. 0 .OOOO 0.0003 0 .OOOO 0.0002 Rhubarb, fresh. 0 .OOOO 0.0000 0.0000 0.0000 Rhubarb, same processed. 0,0001 0,0002 0 .OOOO 0 .OOOO Onions, fresh.. 0 .OOOO 0.0004 0.0000 0.0002 0.0002 0.0008 0.0000 0.0006 Onions, same processed.. Cucumbers, fresh.. 0.0000 0.0000 0,0000 0.0000 Cucumbers, same processed.. 0.0000 0.0001 0 .OOOO 0.0000 Okra, fresh.. 0.0000 0.0000 0.0000 0.0000 Okra, same processed.. 0 .OOOO 0,0000 0 .OOOO 0 .OOOO Processing solutionl.. 0.0000 0,0000 0.0000 0.0000
......................... ........... .......... .... ......... ....... ... ..... ... ................ ....... ........... .. ............... .... ................ ....... ................. ........ ............. .... ................... ..........
...........
The figures obtained on the prepared samples, indicate that carrying out exactly the Official method of distillation is not sufficient to drive over all the sulphur dioxide contained in the samples. The character of the products influencing the amount of sulphur dioxide held back, from I O per cent. for sugar to 2 6 per cent. for flour, the loss due to incomplete distillation in the modified method being 4 per cent. for flour and none for the other two products. With the exception of candies, the modified method gives lower results, although the distillation is more complete. When examining cereals or other products very high in starch, both methods must be modified by either increasing the amount of acid and water or decreasing the amount of the material used, as otherwise the mass becomes semi-solid or pasty. The vegetables enumerated were obtained in the open market. The processing consisted in taking the washed vegetables, breaking or crushing into small pieces, when necessary, and then placing joo grams into Mason jars, pouring on 500 cc. of the hot processing solution, hermetically sealing the jars, and then placing into a boiling water bath for one hour. After cooling, the whole mass was pulped and of this zoo grams, representing IOO grams of the vegetable, taken for each determination, adding in each case IOO cc. water using the official method and 2 0 0 cc. water using the modified method, the amount of distillate being
--_ I
Direct ti- After tration. oxidation. 0,0045 0,0045 0.0037 0.0040 .O .0022 0.0022
9
Direct ti- After tration. oxidation. 0.0050 0.0050 0.0048 0.0048 0.0025 0.0025
Prepared samples.' Sugar and added sulphites Flour and added sulphites.. Starch and added sulphites.. Regular samples 0.0002 0.0006 0 .OOOO 0 .OOOO Gelatine (home-made) Gelatine (French). 0.0270 0.0276 0.0260 0.0260 Gelatine (American).. 0.0130 0.0142 0.0120 0.0121 Meat-fresh 0.0001 0.0004 0.0000 0 .OOOO Eggs-fresh 0.0003 0.0005 0.0000 0 .OOOO Eggs-ageunkno wn 0.0003 0.0008 0,0000 0.0000 Driedfruit ..................... 0.0083 0.0087 0,0078 0.0077 Driedfruit 0.0240 0.0251 0.0228 0.0228 Molasses-bleached 0 . 0 4 5 6 0.0476 0.0410 0.0414 Molasses-bleached ............. 0.0300 0,0307 0.0288 0.0287 Molasses 0.0084 0,0088 0,0079 0.0079 Candy 0,0042 0,0042 0,0047 0.0047 Candy 0.0017 0,0019 0.0017 0.0017 1 Sulphur dioxide added as sulphite: Sugar, 0,0050part per 100 Flour, 0.0050 part per 100 Starch, 0.0025 part per 100
....... ..... ..... ........... .............. ........... ....................
................... ............ ..................... .............
....................... ......................... .........................
1 Processing solution: sugar 5
parts, salt 1 part, and water 100 parts,
84
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y .
exactly 9 cc. for the official method and not less than 400 cc. for the modified method. I n making the direct titration tests for both methods, the distillates were caught in an alkaline solution, and after acidifying with phosphoric acid, titrated with I/IOO normal iodine solution and starch paste as the indicator. When sulphur dioxide was determined by oxidation, including all other volatile sulphur compounds, the distillate was caught in an iodine solution to which a few drops of bromine had been added. This was boiled over a direct flame until colorless and total sulphur compounds precipitated with barium chloride and weighed as barium sulphate. The apparatus was always filled with carbonic acid gas, generating same in the steam boiler from bicarbonate of soda and phosphoric acid. It was found that results obtained in the direct distillation, official method, differed, as the amount of the distillate was increased above 5 cc. Up to a certain, not constant point, a slight increase was obtained by both direct titration and by oxidation. Going beyond that point, the amounts found by direct titration ‘of the excess of iodine, were always above those found by oxidation, showing conclusively .that non-sulphur decomposition products were distilled, due t o further decomposition and that these materially affected the back titration of the excess of iodine. This was further confirmed by the fact that the results obtained when distilling directly into an iodine solution were greater than the actual sulphur dioxide calculated from the barium sulphate precipitate of the same solution and the results obtained by direct distillation into iodine were always higher than those obtained when distilling into an alkaline solution and titrating the sulphur dioxide liberated on acidifying. The amount of sulphur dioxide found by oxidation of a larger quantity of distillate being less than the amount found on titrating the distillate direct, using the larger amount for the determination of sulphur dioxide by precipitation. Volatile compounds, such as essential oils, ethers and oxides, which combine with iodine, effect the accuracy of both methods, but are partly eliminated in the modified method, depending upon their solubility in the alkaline solution into which they are distilled. Such volatile compounds often can be separated by boiling the alkaline distillate, then cooling, diluting to original bulk and, after
acidifying, titrating the sulphur dioxide remaining in the solution. No appreciable error is introduced by boiling the alkaline distillate. The comparative results obtained in the determination of sulphur dioxide and its compounds in food products by the official and modified methods, justifies the conclusions that : I-The Official method for sulphur dioxide, sulphites or sulphurous acid should be changed so as to eliminate the possibility, as has occurred in actual practice, of food products being condemned and rejected by food officials and private persons as not meeting the requirements of Federal and State Food Acts, on account of the presence of sulphur dioxide or its compounds, examined according to the Official method, but containing no added sulphur compounds. 11-Traces of sulphur dioxide or its compounds, or what is found as such, should be ignored as well for all food products as specifically only for meat and meat products.
THE DETERMINATION OF ESSENTIAL OIL AND ALCOHOL IN FLAVORING EXTRACTS. BY
JULIUS
HORTVET AND RODNEY M o m WEST. Received October 15. 1908.
Little is to be found in chemical literature relating t o the determination of either essential oil or alcohol in flavoring extracts. With the exception of extracts of lemon and orange, this field of investigation’ appears to have been in great measure neglected, and it is doubtful whether prior t o 1899 any successful attempts had been made to devise methods of making these determinations. I n a paper entitled “Lemon Flavoring Extract and its Substitutes,”* published about ten years ago, A. S. Mitchell gave two methods for the determination of lemon oil. These methods, somewhat revised, were later adopted as provisional by the Association of Official Agricultural Chemists.S I n 1901,Winton and Ogden4 applied the polariscopic method, as described by Mitchell for lemon extract, to extract of orange, establishing the factor 5.3 for the calculation of the per cent. of oil by volume from the reading on the Ventzke sugar scale. With reference to miscellaneous flavor1 Only those flavoring extracts which consist c h i d y of an alcoholic solution of an essential oil are considered in this paper.
Jour.Am. Chem. SOC., !2l, 1132 (1899). Bull. 107,Bureau of Chemistry, U. S. Dept. of Am., PP. 156-161. 4 Report Conn. Agr. Expt. Sta.. 1901, Part 11, p. 176. f
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