March. 1923
INDUSTRIAL A N D ENGINEERING CHEMISTRY
273
The Protection of Vitamin C in Foods' By Edward F. Kohman R E S ~ A R CLABORATORY, H NATIONAL CANNERSASSOCIATION, WASHINGTON, D. C.
HE destruction of This determination was In studies dealing with the stability of vitamin C toward heat, made by subjecting the milk vitamin C in cookoxygen and other factors have not been excluded. I f is therefore imto a vacuum in an inverted, ing processes is compossible to say to what extent the destruction noted is due to oxidaround-bottom, 1ong-ne c k e d monly ascribed to a comtion and to what extent it is due to heat, but i f has been dejinitely flask, with a total capacity of 1220 cc., carrying a rubbination of oxidation and proved that oxygen has a marked destructive action during heating. ber stopper with two tubes, heat and seems also to be I n the future experiments the oxygen contained by the product to the one an outlet tube to affected by the degree of be studied, as well as that in the cooh$tg water, should be tohen info which the vacuum was apacidity, The data herein plied and the other an inlet account. tube through which air-free presented are in agreeBoiling for several minutes will remove the oxygen from water water was admitted to fill the ment with the view that as Iong as it is kept hot. To remove the oxygen from milk., fruit vacuum and drive the gas oboxidation plays an imporjuices, and other liquid foods without the application of heat, a tained into an Orsat appatant role. They seem to ratus. Each tube carried a vacuum exhaust with mechanical agitation or a suficient vacuum to glass stopcock. 4 vacuum justify the statement that cause ebullition must be applied. To remove the oxygen from applied to a liquid in this as yet no one has given solid food products without heat, they may be subjected to a high manner without agitation any conclusive evidence vacuum under water for considerable time with adequate agitation to will not remove appreciable that heat in itself, within amounts of gas for a long otlercome supersaturation, or a vacuum may be applied without time. A state of supersatranges of temperature used covering with water and then released with nitrogen. Subsequent uration results and gas bubin cooking and canning, exposure to the atmosphere must be avoided. Respiration of bles collect only slowly on exerts more than negligible fruits and oegetables may also be utilized to deprive them of oxygen. the inner surface of the condestruetive action in acid tainer, depending upon the degree of cleanliness of that products, such as fruits, for the simple reason that no one has as yet excluded surface. But if the container is jarred by blows from the hand, bubbles form throughout the liquid, which is practically the effect of oxidation or other destructive agents when small exhausted in 3 to 5 min. testing the effect of heat. This statement should not The experiment recorded in Table I1 with water illustrates be construed as a contention that heat in itself plays no this characteristic of a liquid. part in this respect. It is merely intended to point out The gas in Fraction 1 was obtained by subjecting distilled that present data do not enable us to definitely evaluate the water to a vacuum of 28 in. for 3 min., during which time the various destructive agents. container was kept quiet. The gas in Fraction 2 was subseLaMer's2 experiment, in which he bubbled hydrogen quently obtained from the same sample of water by subjecting through tomato juice, would have thrown light upoii this it to a 28-in. vacuum for an additional 3 min., during which time the container was jarred. Neither fraction accurately reprequestion if he had shown that the dissolved oxygen was sents the gas obtained from the entire contents of the flask completely washed out before the heating began, and if the (1220 cc.), because water was gradually drawn out of the flask as the air collected in the upper portion. This amounted to hydrogen itself had not had a destructive action. Hem3 apparently attaches considerable significance to the considerable for Fraction 2, as 16 cc. of gas measured under conditions would occupy considerable volume when a t oxidation of vitamin C in the pasteurization of milk in contact standard room temperature and under the vacuum used. with air as well as in subsequent storage. If his view is TABLE 11-GAS OBTAINED PROM DISTIT LED WATER BY A 28-IN. VACUUM FOR 3 MIN correct, then it certainly is very important to pay attention Oxy- Nitroto the oxygen which is dissolved in the milk just previous to Total Oxy- Nitro- COz gen gen Gas COz gen gen Per Per Per pasteurization; but to our knowledge no one has made any Cc. Cc. Cc. Cc. cent cent cent TREATMENTTOOBTAINGAS reference to this. 2 5 . 0 75 0 Fraction 1, container quiet 0 2 0 6 0 0 0 7 0 0 5 0 10.8 1 2 31 4 6 7 . 4 Fraction 2, container jarred 16.0 0 2 EXTENT OF DISSOLVED OXYGEN I N MILK.4ND WATEB DESTRUCTION I N FIRSTPARTOF HEATING PERIOD T o show the extent of this dissolved oxygen, the gas was MARKED determined and analyzed as it occurred in milk taken from Delf4 did the earliest extensive work on the rate at which the vat in a large milk plant in Washington just previous to vitamin C is destroyed by cooking. She summarizes her and after a period of heating corresponding to pasteurization. work with cabbage as follows: The results are given in Table I. TABLE111-THE Loss OF VITAMIN C I N COOKING CABBAGE
T
Time of Cooking Hrs.
TABLEII-GAs Total Gas
Cc. 18.2 12.9
1
tions.
OBTAINED FROM FRESHMILKF Y A 26-IN. VACUUM FOR 5 MIN WHILE CONTAINER WAS JARRED Oxy- NitroOxy- Nitro- COa gen gen COz gen Ken Per Per Per TREATMENTBEFORE DECc. Cc. Cc. cent cent cent TERMINKG GASBYVACUUM 2.5 3.2 1 2 . 5 13.7 17.6 6 8 . 7 Unheated milk taken from vat in dairy just previous t o Pasteurization 0.8 2.0 10.2 6 . 2 15.5 7 8 . 3 Samemilkafter heating 10 min. at 70' to 165" and then 30 min. a t 16z' F. The volumes of gas in all tables in this paper are for standard condi-
-_
1 Presented before the Division of Agricultural and Food Chemistry at the 64th Meeting of the American Chemical Society, Pittsburgh, Pa., September 4 to 8, 1922. 2 J . A m . Chem. Soc., 44 (1922), 172. 3 THISJOURNAL, 13 (1921), 1115.
Temperature
1
1 1 '/a
1
1/3
1
2
c.
60 70 80 90 90
100 100 100
2
110 120 120
1 2
130
1 1
130
Vitamin C Destroyed Per cent 70 90 90 70 More than 90 70 Less than 90 Less than 90 Less than 90 Less than 90 Less than 93 93 93 to 97
The striking feature of this table is that there is scarcely any noticeable difference between the effect of cooking 1 hr. at 70" C. and higher temperatures up t o 2 hrs. a t 120" C. 4
B i o c h e m . J , 12 (1918), 416.
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Vol. 15, No. 3
INDUSTRIAL A N D ENGINEERING CHEMISTRY
274
Attention is called here to the fact that the cooking of cent less dense than a t 25" C., or room temperature. Even cabbage requires considerable water, which always has more or a t 100" C. the vapor pressure of tomato juice would be apless dissolved oxygen, while tomatoes are canned without the preciably less than atmospheric pressure. If it is recalled that LaMer found the destruction of vitamin addition of any water. Comparing the published figures as to the vitamin-C content of raw tomatoes and of canned C complete in 1 hr. a t 100" C., when oxygen was bubbled tomatoes, and judging from the statement of LaMer5 that the through at atmospheric pressure, whereas 50 per cent was canned tomatoes used by him were equal or slightly superior destroyed when no oxygen was passed through and for the to the raw product raised in his garden, it does not seem next 3 hrs. the per cent destruction rose only to 67.7, one is probable that there is any appreciable loss of vitamin C in the led to believe that both in his experiments and in those of canning of tomatoes. This protection in tomatoes is com- Delf a considerable portion of the destruction which may monly ascribed to their acidity. But if we consider that have occurred during the first part of the first hour was due water always has dissolved oxygen and raise the question as to dissolved oxygen, and that the subsequent slower destructo the possible effect of this in cooking cabbage, and a t the tion was in part due to atmospheric oxygen. same time bear in mind that the acidity of tomatoes did not ELIMINATION OF OXYGENBY VACUUM protect them when oxygen was bubbled through during the heating period, as was shown by LaMer,e we cannot but For this reason experiments dealing with the stability of infer that there may be another factor which is as important vitamin C toward heat must take into account the oxygen as the acidity or heat-namely, oxidation, and more especially in the product and in the cooking water, as well as atmosthat caused by the oxygen in solution in the cooking water or in pheric oxygen. Boiling for several minutes will eliminate the product. This inference is strengthened by the fact the oxygen from the cooking water, but when heating below that Deli's results do not indicate any marked difference in the boiling point the gases may be retained for hours in a destruction when the time and temperature are increased from supersaturated state. 1 hr. a t 70" C. to 2 hrs. a t 120" C. Heat, of course, cannot be applied to eliminate oxygen from LaMer determined the rate of vitamin-C destruction when food products if the effect of heat on the vitamins is to be the juice from canned tomatoes was heated at 60", 80", and studied, or if the aim is to conserve the vitamins in any food 100" C. The tomatoes were first strained through muslin industry. A vacuum exhaust may be utilized, but a vacuum and then filtered through paper. The heating was done in is not successful unless the container is jarred to break up the Erlenmeyer flasks closed with cotton plugs and placed in a supersaturated state in which the gas will persist for a long water bath. time, or unless the vacuum is sufficient to cause ebullition. I n interpreting LaMer's results with a view to determining As an illustration, two experiments are given in Table IV, how far the destruction he noted was due to heat and how one with red raspberries, a product in which much air is far to oxidation, it should be borne in mind that his tomato trapped, and the other with unpitted sweet cherries, in which juice was exposed sufficiently before the heating began to air is not so apt to be mechanically held. dissolve more or less atmospheric oxygen, and that liquids In order to determine the gas in these fruits they were placed heated below the boiling point may retain dissolved gases in in a wide-mouthed Erlenmeyer flask, covered with water, and a supersaturated state for a long time. When fruit juices, closed with a two-hole rubber stopper. One hole carried an such as tomato juice, containing dissolved oxygen, are heated, inlet tube with a glass stopcock, and in the other hole was inthe oxygen interacts with them. This does not justify the serted-the inlet tube of the flask described above. At the end conclusion, however, that this oxygen is no longer in a form of each fraction the Erlenmeyer flask was completely refilled with water through the inlet tube, thus driving any gas collected in which it may exert a destructive action. We must con- under the stopper up into the receiving bulb. The size of the sider the possibility of its having raised the oxidation po- receiving bulb may be suited to the amount of gas obtainedtential, which LaMer suggests as a possible measure of the a 500-cc. bulb being used in these experiments. Each succeeding fraction was obtained by reattaching the receiving bulb and again destructive action of a medium. applying a vacuum. The container was kept quiet for every Moreover, diffusion of atmospheric oxygen can readily fraction except the last, to obtain which the Erlenmeyer flask take place thyough a cotton plug, and the vapor pressure of containing the fruit was held by the neck in the left hand while the tomato juice in LaMer's experiments only in part dis- the lower edge was given rather sharp blows with the palm of the placed atmospheric pressure. The vapor pressure of tomato right hand. In Expt. 1, 350 g. of berries were used in a 600-cc. flask, while in Expt. 2, 600 g. of cherries were used in a 950-cc. juice is less than that of water. At 60" C. the vapor pres- flask. sure of water is approximately only one-fifth of the atmosIt will be noticed that as much or more oxygen was obpheric pressure, while a t 80" C. it is considerably less than one-half of the atmospheric pressure. It is true that the tained in the last fraction as the total of the other fracdensity of atmospheric oxygen would be decreased by ele- tions, and many times more than in the immediately precedvated temperature but not enough to make it negligible. At ing fraction in which the time and vacuum were the same. 60" C. oxygen would be 10.5 per cent, and at 80" C., 15.5 per Air-free water was not used in these experiments. The oxygen, therefore, came in part from the water. This, however, 6 Dissertation, Columbia University, 1922. does not alter the general principle involved. The large 6 THISJOURNAL, 18 (1921), 1108. TABLE IV-GAS OBTAIXED~FROX FRUITS Fraction No.
Time of Exhaust Min.
1 2 3 4 51
0.5 0.5
1 2 3 4 5'
0.5 0.5 0.5
1
0.5
3.0 3.0
3.0
3.0
Vacuum during Exhaust In.
Total Gas cc.
15 20 27 27 27
6.3 1.9 3.9 4.3 13.0
15 20 27 27 27
8.9 6.1 9.2 11.3
Container jarred for Fraction 5 .
0.0
co1
cc.
Nitrogen Oxygen cc. cc. E x p l . 1-Red Raspbevvies
0.0 0.0 0.3 1.0 5.1 Expt. 2-Swee: 0.0 0.6
1.1 3.4 4.8
0.5 5.8 1.8 0.1 3.5 0.1 3.2 0.1 7.1 0.8 Cherries (Bin& 0.0 0.0 7.4 0.9 4.7 0.3 5.5 0.3 4.5 2.0
coz
Per cent
0.0
Oxygen Per cent
Nitrogen Per cent
7.0 22.9 38.9
8.6 4.8 2.3 4.2 6.2
91.4 95.2 90.7 72.9 54.9
0.0 7.1 17.9 37.9 42.8
10.2 4.5 3.9 16.9
'D. 0
0.0 82.7 77.6 58.2 40.3
0.0
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
March, 1923
amount, of gas obtained in the first fraction with a low vacuum in the case of raspberries is d u e t o trapped air. The processes used in the canning industry lend themselves conveniently to the exclusive use of boiled water. In many factories it has been the custom to boil the water used for canning. This should be adopted in all factories.
RESPIRATION OF FRUITS AND VEGETABLES The active respiration which takes place in fruits and vegetables tends to keep down the amount of dissolved oxygen in them, and also to leave the nitrogen, which is less soluble than oxygen, to fill the interstices. We have made determinations on certain fruits and found them practically free from oxygen, while in others we have found the gases to have practically as high oxygen content as the atmosphere and the total gas to be over one-fourth the volume of the fruit. We have found that green lima beans and peas (unbroken seeds), green corn cut from the cob (broken seeds),
275
carrots (tubers) scraped and cut into disks, and cabbage (leaves) cut into slaw, if covered with an equal weight of water saturated with atmospheric oxygen, will, a t room temperature, not only contain no oxygen themselves, but will have extracted all the oxygen from the water also a t the end of 2 hrs. No examination was made for shorter periods. The possibility should not be overlooked, however, that such active respiration might result in a more destructive medium, perhaps by an increased oxidation potential or similar condition. If this does prove to be the case, it suggests the possibility of preparing a more favorable condition for the protection of vitamin C, by allowing respiration for a time in an atmosphere of nitrogen. A study of this question and its application to canning is contemplated. The gases in fruits and vegetables can readily be replaced by another gas by subjecting them to a vacuum and releasing the vacuum with the desired gas, but diffusionis quite rapid in some cases and subsequent exposure to the atmosphere must be avoided.
Estirnation of Caramel in Sugar Products-Criticism
of the Ehrlich Method’
By George P. Meade CUBAX-AMERICAN SUGARCo., CARDENAS, CUBA
HRLICH’S method for the colorimetric estimation of caramel in sugar products is described by Brownet as follows : Saccharan, one of the component parts of caramel, is made by heating sucrose to 200 O C. in an oil bath under vacuum, and then extracting with hot methanol. The residue is then dissolved in hot water, evaporated, and ground to an amorphous powder, the powder representing about 20 per cent of the original sucrose. Ehrlich says that saccharan is not precipitated by lead subacetate; therefore, the coloring matter remaining in any lead-clarified filtrate is due to saccharan, which can be estimated by color comparison with a standard saccharan solution. The amount of sucrose that has been destroyed by heat will be approximately five times the amount of saccharan determined. All attempts to use this method on solutions containing known amounts of caramel or saccharan proved it to be valueless. A typical case follows: Five grams of saccharan, made according to Ehrlich’s directions, were dissolved in one liter of water, and a part of this strong solution was diluted 1:50 as a standard for color comparison. Two and one-half normal weights of a dark molasses were dissolved and made to 500 c ~ . and , 100-cc. portions were pipetted into each of three 200-cc. flasks. To the first no saccharan was added, to the second 20 cc. of the strong solution (0.1 g. saccharan), and to the third, 60 cc. (0.3 g. saccharan). To each were added 20 cc. of 54“ Brix subacetate of lead solution-an excess of lead being purposely used-after which all were made to the mark and filtered. Quantitative color determinations were made on each of the three filtrates by comparison with the standard saccharan (dilute) which contained 0.0001 g. per cc. The amount of saccharan contained in each filtrate was as follows:
E
PREPARATION OP M O L A S S SOLUTION ~S 100 cc. molasses plus 20 cc. lead t o 200 CC.. 100 cc. molasses plus 20 cc. saccharan solution plus 20 CC. lead t o 200 cc 100 cc. molasses plus 60 cc. saccharan solution plus 20 cc. lead to 200 CC... .
. ... . . . . . ..... . ..
-
1 Presented
Saccharan in Total Filtrate by Comparison with Standard Saccharan (Ehrlich’s Added before Method) Lead G. G.
Per cent Added Saccharan Precipitated by Lead
0.0175
None
....
0.0220
0.1
95.5
0.0375
0.3
93.7
before the Division of Sugar Chemistry at the 64th Meeting of the American Chemical Society, Pittsburgh, Pa., September 4 to 8, 1922. 8 “Handbook of Sugar Analysis,” p. 467.
When 5 cc. more of lead were added to the three filtrates, the color of all three after filtration was practically the same, showing that all the saccharan is precipitated if sufficient lead is added. Caramel was prepared in three different ways-by heating sucrose to constant weight at 180’ C., by heating to 190” C., and by heating to 200’ C. in a vacuum,2 and all behaved the same as the saccharan when added in known amount to molasses solutions and then clarified with lead. In every instance the lead removed a part or all of the color, depending on the amount of lead used. Saccharan behaved identically like the various caramels made in different ways, so hereafter caramel only will be referred to, with the understanding that saccharan is included. The following work with caramel shows why the Ehrlich method is of no use: Caramel dissolved in recently boiled, distilled water is not precipitated by lead subacetate. However, when any of the common deleading agents are added t o the caramel solution before clarifying with lead, the resulting precipitate carries down with it all, or nearly all, of the color. Sodium carbonate also acts in this way if not present in t o o great excess. With hydrochloric, sulfuric, or phosphoric acids, the lead removes little, if any, of the color. Caramel dissolved in a tap water high in solids was almost completely removed by the addition of lead. Apparently, anything that will set up a voluminous precipitate with lead will remove part or all of the caramel from the solution, provided the reaction of the filtrate is not too strongly acid or alkaline. A series of experiments using normal lead acetate instead of lead subacetate proved that the normal lead acts in the same way as the basic lead-i. e., caramel is removed from the solution by the normal lead, provided material is present which sets up a precipitate with the lead. Ehrlich evidently assumed that the caramel in a sugar solution would not be removed by lead, because he found that the lead did not precipitate saccharan in pure solution. The work here reported proves that the ordinary impurities which are found in molasses and dark-colored sugar products, when precipitated by lead subacetate or normal lead acetate, carry down with them all or nearly all of the caramel in the solution, and that therefore the method of Ehrlich is valueless.
