June, 1922
THE JO URiVAL OF I N D UXTRIAL A N D ENGINEERING CHEMISTRY
that observed in untreated eggs to 6.2, 3.7, and 14.8 per cent, respectively. Two grams of soap added to 100 cc. of mineral oil C lowered the loss from 35.8 to 6.2 per cent. It is thus evident that, soap will effectively close the pores if it is applied in a witable medium. Attempts to raise the value of mineral oil A by additions of gums, waxes, and rosin were not successful. The results, as shown in Table IV, indicate that nothing is to be gained by such modifications when applied to relatively heavy mineral oils similar to that used in the test. The temperatures of storage used in this investigation are much higher than those employed for the cold storage of eggs, tho object being to pi-oduce a maximum effect in a comparatively short period of time. The methods which were here found to be useful in retarding shrinkage can be applied
527
to the.study of the origin of the characteristic odor and flavor which develop in eggs during cold storage. TABLE IV-EFFECT OF VARIOUSGUMS WAXES
AND ROSIN ON THE ERFIHEAVY MINERALOIL IN) PREVEdTING SHRINKAGE I N EOGS Loss in Weight dur- Comparative Loss in ing Storage for 12 Days Treated and Ona t 40' C. treated Eggs IMMERSION FLUID^ Grams Per cent (Untreated = 100) Mineral oil A , , 0.20 0.4 4.0 100 cc. mineral oil A plus: 1 g. gum guaiac.. 0.19 0.4 4.0 2 g. gum mastic.. 0.20 0.4 4.0 4 g. spermaceti.. . 0.24 0.4 4.0 4 g. beeswax. . 0.26 0.4 4.0 4 g. spermaceti 1 g. gum damar.. . . 0.26 0.5 5.0 4 g. beeswax+l g. gum damar. . . . . . . 0.30 0.5 5.0 1 g. gum damar.. . . . 0.30 0.6 5.9 4 g. beeswax+lg.rosin 0.36 0.7 6.9 Untreated.. , . 3.11 10.1 100.0 1 The eggs were treated by Method I1 (footnote, Table 111). CIENCY OF A
. . . . . . . .. ...... .. .. . . .+. .. .. .. .. ..... . . . . .. .. . . . . .. . . . .
Method for Determining Hydrogen Sulfide Evolved by Foods when Cooked at Various Temperatures' Its Application to Steam Distillation under Pressure By Edward E. Kohman RESEARCHLABORATORY, NATIONALCANNERS'ASSOCIATION, WASHINGTON, D. C.
The following paper describes a method for the accurate deferminaffionof the hydrogen sulfide evolved when foods are cooked at 100' C. or higher. I f involves the distillation of the sample with steam under pressure, and the gravimetric determination of the sulfide as barium sulfate. Green corn, which was the food product used in the experiments, gives considerable quantities of substances other than hydrogen sul.jide which reduce potassium permanganate. and this method makes a study of these products possible. i t is further suggested that the method and apparafus described in this paper may be applicable in the separation of many organic mixtures, or in distillations such as are involved in the determination of yolatile futfy acids, where uniform amounts of distillate in a given time are desired.
N the study of the black discoloration due to the formation of ferrous sulfide which occurs in the air space of canned corn and of lye hominy, as well as in the grains of the latter, it was desirable to know the amounts of hydrogen sulfide formed during the processing of these products. A very satisfactory method has been devised, of such general application that it may be used a t any temperature and for any volatile product which permits of steam distillation. The food product to be heated is placed in a 3-1. flask, which is set in an upright autoclave or retort, supplied with steam from a boiler. (Fig. 1.) Since cork contracts in steam a t high temperatures, the flask is fitted with a pine wood stopper, c, which contains two holes fitted with glass tubes, a and b. Tube a extends below the stopper to the bottom of the flask and terminates just above the stopper with a right-angled bend. This bend prevents any water which may condense on the under surface of the cover of the Tetort from dripping into the tube. The tube opens into the Tetort; therefore steam surrounding the flask enters it as the pressure is relieved by a stopcock on the other tube. Tube lb terminates just below the stopper and extends above through the cover of the retort. It should be long enough so that the flask can be put in position before the cover is completely
I
1 Received January 18, 1922. Presented before the Division of Agricultural m d Food Chemistry at the 63rd Meeting of the American Chemical Society, Birmingham, Ala., April 3 to 7,1922.
down. Outside the retort, this tube enters a Kjeldahl connecting bulb and then is bent to an angle of about 75', and to it is sealed a glass tube with a stopcock. Condenser g, which leads to a bromine solution, follows. The steam is turned on rather rapidly when heating is begun, but the cover is not clamped down tightly until after about half a minute, so as to allow the air to escape from the retort. By means of this apparatus a temperature of 120' C. can be attained in 2 min., and the distillate can be regulated a t will, while the amount of water in the flask remains constant. It was planned to collect about 650 cc. during a 45-min. distillation period a t 120" C. At the end of the distillation, the r e t o r t should be opened as soon as the pressure is relieved; otherwise the suction produced will draw the liquor out of the flask. The sulfur is determined gravimetrically as barium sulfate. One further improvement is s u g g e s t e d . When the steam is turned on rapidly in the retort, the cover is not clamped down until most of the air has been allowed to escape. But the air in the flask must e s c a p e through the outlet tube. If the expansion of the air is greater than can be relieved by the outlet, the back pressure may force FIG. 1 the liquor out of the
T H E JOURNAL 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
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the outlet flask through tubethe must inletalways tube. beConsequently, opened wide for thea stopcock few seconds on
Temperature of distillation,
e
H g i n distillate, p. p e r l . HzO
and gradually closed as the temperature comes up. This need of regulating each time Causes a little variation in the distillate. Where it is essential to have an exact and uniform amount of distalate, it can be obtained by using a outlet; one branch, d in the figure, is a largetube with a stopcock^ the other, e, is a tube of the desired diameter. ~~~h should enter the condenser. With this arrangement, the amount of distillate will vary only with the different temperatures in the retort, In distfilat,ions like that involved in the determination of volatile fatty where uniform amounts in a given time are desired, method should prove very accurate, for the temperature of retort supplied with from a boder can be exactly regulated;to a degree not possible with the Bunsen burner or hot plate. After the work recorded in this paper was completed, an article by Masters and Garbutt2 was noticed, in which different attempts to determine the hydrogen sulfide formed in cooking foods are described. These authors conclude:
a
It appears hardly Possible t o obtain a reliable measure of the amount of hydrogen sulfide produced during cooking, but it was thought that if some method, which did not involve a distillation process, could be devised, it might be possible to obtain a measure of the amount of sulfide left in the cooking water a t the end of the experiment and that if all experiments were carried out under the same conditions such information might be of value for comparative purposes, even though it did not represent the total amount of sulfide produced during cooking. For this purpose a modification of the method described by Wimplera was adopted, and was found to give more consistent results than the methods previously described.
The modified method which they finally adopted was to cook 100 g. of the vegetable in 750cc. of water with a reflux condenser for 1 hr., knowing that some hydrogen sulfide was escaping and some was undergoing decomposition. Carbon dioxide was then bubbled through a measured amount of the cooking water and passed through a hydrogen peroxide solution. The hydrogen sulfide was oxidized to sulfuric acid, which was titrated with 0.01N sodium hydroxide. The method described in the present paper meets the requirements of a distillation process, described by Masters and Garbutt as "hardly possible." Air does not have access to the cooking food to cause decomposition of the hydrogen sulfide, which is carried off as it is formed, by a rapid current of steam. Masters and Garbutt observed that the distillate from foods contained acids other than hydrogen sulfide; these, however, do not interfere when the sulfur is determined' gravimetrically as barium sulfate. The method is applicable at all temperatures above 100' c. and should be useful in a variety of Cases- It Will make Possible a study of other volatile products evolved in the cooking of foods. STEAM DISTILLATION UAQER PRESSURE In the separation Of many Organic mixtures, a distillation process at elevated temperatures ought to be applicable when the usual steam distillation a t atmospheric or reduced pressure is of little or no value. As an illustration, the effect of such elevated temperatures in distilling the immiscible liquids, water and mercury, is given in Table I. The amount of mercury in the distillate was cal'datedfrom the vapor pressures by Of Avogadro's Law. Since the gram molecular volume varies directly, and in the same proportion, as the vapor pressure, we may formulate the equation Wt. of Hg in distillate = Wt. of Hz0 in distillate Bzochem. J., 14 (1920), 76 a A ~ Q Z Y S ~ , (19171, 26. 2
iz
Vol. 14,No. 6
.. . . . . . . . . 100 . . . , . . .. ...... 3 . 9
C . .TABLE . I
120 150 5.4
8.3
200
230
16.2 22.8
In Table 'I are given similar figures for Some organic cornpounds. It is evident that with hromobenzene and chlorobenzene the distillation would be better carried out at 100" C . , but the reverse is true for iodobenzene. Assuming for the purpose of illustration a mixture of these three compounds to be immiscible in water and in each other, a steam distillation at the lower temperature would concentrate the dorobenzene in the distillate, whereas a t the higher temperature it would concentrate the iodobenzene in the distillate. Since these three compounds are not immiscible in one another, it be predicted what would happen if such a mixture were subjected to steam distillation a t various temperatures. Although under reduced Pressures applied, distillation under pressure is scarcely considered. In many cases the possibilities of decomposition make the lower temperatures necessary. But the lack of a simple method of distillation under pressure is undoubtedly a factor in its not being used. An application of this method to some organic mixtures is certain of som'e interesting results. Many separations that are not successful by present methods might be effected. Tarry masses Often yield more products and no doubt in some cases products which would otherwise be lost, TABLE 11-STEAM
n I S T I L L A T I O N OF O R O A N I C COMPOUNDS
. ........ .. .. .. .. 750 100 ....... .. ..., 2410 1620
Temperature of distillation ' C C e H 6 1 in dlstilldte, g. Per 1.'HZO.. CeHsBr in distillate, g. per 1. HzO.. c e ~ 6 C in i distillate, g per I. H Z O . .
120 150 200 230 810 870 960 1000 1610 1580 1540 1530 2280 2100 1880 1780
COOKING OF GREENCORN Results on 200-g. samples of lye hominy in 300 cc. of water are given el~ewhere.~In Table 111 are the results obtained by cooking 1000 g. of fresh corn in the canning stage in 500 cc. of water and collecting the distillate in half-hour periods. TABLE111-HYDROGEN SULFIDE EVOLVED WHEN GREENCORN Is COOKED AT VARIOUSTEMPERATURES TEMP. MG.SUGFUR PER 1000 G. CORN, IN o ~ - H RPERIODS . No. OC. 1st 2nd 3rd 4th 5th 6th 7th 8th
SAMPLE
1 2
121 121
25
105
7
103
:;$ ;: ;g
6.40 8.83 5.28 6.5s 3.90 2.91 3.19 8.12 2.57 1.72 1.02
4 . 5 3 1.40 5.02 1.81 3.50 1.97 4 . h 2.60 3.20 1 9 8 2.34 1.88 3.12 1.80 6.53 3.78 2.36 1.36 1 29 0.88 0 . 7 1 0.49
1.28
1.75
1:s; 1143 1.50 2.94 0.96 0.55 0.58
1.10 1.62
0.99 1.14
i:i4
i'ii
1.29 1.11 1.28 1.14 1.00 1 17 2.06 1.84 0 . 7 1 0.74 0.54 0 49 0 47 0 36
1:hO
0.58 0.82
1.35 i:i4 1 . 0 3 0.85 0.91 0.91 1.02 1 . 0 7 1.02 0.83 0.60 0 . 5 2 0.47 0 . 4 9 0.36 0 . 4 9
Samples 1 and 2 are different lots of corn and show that the amount of hydrogen sulfide evolved varies considerably for different lots of corn. Samples 2 and 3 are the same ears, one end of the ears being used for one and the other end for the other sample. The butts and tips of the ears were apportioned equally between them. By comparing the two the effect of temperature is noted. Samples 4,5, and 6 are from the same ears, and Samples 5 and 6 are the same corn mixed after being cut from the ears. These also show the effect and l l are all from the of temperature. Samples 9, sample of corn, cut from the cob and mixed before dividing it between the three. Sample however, was given a 40min. process a t 250' F. and Sample 11 an 80-min. process a t 2500 in an open flask in a retort before hydrogen sulfide was determined. It is evident that the hydrogen sulfide escapes from the even though no current of stem is passing through. From a comparison of all the figures, it is evident that considerably more hydrogen sulfide is evolved during 200 X vapor pressure of Hg a t T" the first half hour than during the second and that the amount 18 X x'a~orpressure of H20 a t To' decreases for each succeeding period. Masters and Garbutt2 state that the amount of hydrogen sulfide evolved when the 4
THIS JOURNAL, 14 (1922), 415.
