I N D U S T R I A L A N D ENGINEERING CHEMISTRY
April, 1930
355
Relative Merits of Sucrose, Dextrose, and Levulose as Used in the Preservation of Eggs by Freezing' 0. M. Urbain a n d J. N. Miller URB~IN LABORATORIES, COLUMBUS,OHIO
A
NUMBER of protective (non-coagulating) agents are used in the freezing process of preserving eggs, the most common being the sugars, sucrose and dextrose. Levulose is also employed and, with prospects bright for a cheaper product, may come into general use. It is well known that when egg batter containing the yolks is frozen without the addition of a protective agent the egg structure is broken down and the thawed batker is watery and ropy. The authors have found this condition to be due to the dehydration and coagulation of a yolk substance, lecithoprotein. Egg batter containing the yolks that has been frozen without the addition of a protective agent is unsuited for use by bakers, salad-dressing manufacturers, or others who demand a product that can be intimately incorporated in such carriers as milk and the various oils. In order to determine the relative merits of sucrose, dextrose, and levulose as used in the freezing process of egg preservation, it was thought best to investigate the following phases: (1) To isolate and identify the constituents responsible for the breakdown of the egg structure on freezing. ( 2 ) To determine the relative merits of sucrose, dextrose, and levulose when used to prevent the breakdown of the physical structure of the substances isolated and identified under (1). (3) To determine if the sugars used as protective agents can be washed from the thawed batter. (4) To determine the amount of free water which can be removed from thawed batters previously frozen with and without protective agents. ( 5 ) To determine the rate of fermentation and bacterial decomposition in thawed batters following the use of sucrose, dextrose, and levulose as protective agents. C o n s t i t u e n t s Responsible f o r Breakdown
The whites and yolks of five fresh eggs were separated and each portion was stirred into a batter separately. Each portion was placed in a flask, plugged with cotton, and frozen a t -15' C. They were maintained a t this temperature for 72 hours after which they were thawed. On thawing it was found that the white portion had undergone no apparent change. The yolk portion, on the other hand, was no longer homogeneous in character but was watery and ropy. ,Vote-Experiments were made with yolk batter which had been frozen for 15 months. When thawed this batter exhibited the same physical characteristics as t h a t that had been frozen b u t 72 hours. This indicates t h a t the changes take place either during the freezing or the thawing, or during both of these processes, and not while the batter is in the frozen state
The yolk portion was transferred t o a muslin filter and washed with cold distilled water until the waqhings were clear and colorless. At this time the ropy mass on the filter had a volume about one-twentieth of that of the original yolk batter. The ropy material on the filter retained its yellow color, indicating that the lutein was a t least in part retained. The coagulated mass was next extracted with ether. Five extractions served to completely remove the lutein. The ether peptized the other substances present and separated itself into two layers. The upper layer was drawn off and concentrated. On addition of acetone to the concentrated ether solution, a substance precipitated which was found to be soluble in cold absolute alcohol. This ma-
' Received
December 13, 1929.
terial was thus identified as lecithin ( I ) . The lower portion of the ether solution was evaporated to dryness and found to contain only a trace of solid matter, indicating that a very large percentage of the ropy material was lecithin or a lecithoprotein. Relative Merits of Sugars i n Preventing Breakdown of Isolated Substances
The lecithin from the yolks of ten fresh eggs was prepared as described above. Four grams of this material were dispersed in 40 cc. of distilled water and 10 cc. transferred to each of four culture tubes. To each of the first three tubes was added, respectively, 1 gram of sucrose, dextrose, and levulose, and to the fourth tube no protective agent was added. The sugars were thoroughly incorporated in the mixtures, which were then frozen a t -15" C. for 72 hours. After thawing the mixtures were filtered through close linen filters and thoroughly washed with cold distilled water. The filters with contents were dried in a warm current of carbon dioxide in a drying oven. The amounts of coagulated material recovered are given below: SUGAR Sucrose Dextrose Levulose N o sugar
LECITHINCOAGULATED Gram 0.988 0,008 0.006 0.996
The results indicate that practically all the lecithin is coagulated when no protective agent is employed, that 98.8 per cent is coagulated when sucrose is added, and that not to exceed 0.8 per cent is coagulated when the protective agent is dextrose or levulose. A t t e m p t t o Wash Sugars f r o m Thawed B a t t e r
The yolks of four eggs were stirred into a batter and 10.000 grams of the batter weighed into each of four culture tubes. As in the preceding experiment, 1 gram of the respective sugars was added to each of the first three tubes and none to the fourth. The sugars were mixed through the batters, the tubes were plugged with cotton, and all the samples were frozen a t -15" C. for 72 hours. On thawing the samples were transferred to ultra-filters of correct porosity-that is, the pore diameter was such that the sugars in solution passed through readily while the egg colloids and emulsified fat particles were retained. The contents of each ultra-filter were washed with 1 liter of cold distilled water. The ultrafiltrates were diluted to a known volume and an aliquot portion was taken for determination of the sugar content by the method of Pavy. The amount of sugar washed from each batter follows: SUGAR Sucrose Dextrose Levulose No sugar
SUGARRECOVERED Gram 0.970 0.978 0.980 0.006
A small amount of dextrose was recovered from the blank, due no doubt to the washing out of the normal dextrose content of the eggs. The results indicate that the sugars used as anti-coagulants do not enter into permanent combinations with the egg substances.
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
356
Free Water Removed from Thawed Batters
Eighty grams of yolk batter were divided into four 20-gram samples. To each of the first three samples 2 grams of sucrose, dextrose, or levulose were added and to the fourth no protective agent was added. The samples were placed in tightly stoppered flasks and frozen a t - 15" C. for 72 hours. After thawing the samples were transferred to four ultrafilters. The ultra-filters were made by coating alundum extraction thimbles with collodion. The thimbles were fitted into thistle tubes with sections of rubber stoppers. Into the bell part of the thistle tubes side tubes were sealed to serve as connections to suction pumps. The stems of the thistle tubes were cut off short and 5-cc. tubes graduated to 0.01 cc. sealed on in their place. When the thimbles were fitted into the apparatus and suction was applied, water from the batter flowed down the walls of the thistle tubes and into the calibrated tubes. The volumes of water collected in the graduated tubes were determined by hanging the pieces of apparatus in a thermostat bath a t 20" C. for 1/2 hour and then reading the levels in all the tubes simultaneously. During the applcation of suction the tubes were immersed in an ice bath to minimize evaporation. The amounts of water recovered from the various samples are given below: BUGAR
WATERRECOVERED
cc.
Sucrose Dextrose Levulose No sugar
3.80 3.00 2.95 3.92
The results indicate that dextrose and levulose are more effective than sucrose in preventing the formation or liberation of free water in the process of egg preservation by freezing. Fermentation in Thawed Batters Following Use of Sugars
The yolks of fifty eggs were stirred into a batter, which was then divided into three equal portions and each portion transferred to a sterile flask. To each portion 10 per cent by weight of one of the sugars was added. The flasks were plugged with cotton and frozen a t -15" C. for 72 hours. The three samples were then incubated a t 22" C. and samples were withdrawn periodically for the determination of alcohol
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and for bacterial counts (at 37" C. on agar). The results are given below: SUGAR Sucrose Dextrose Levulose
PERIOD ALconox. Hours % y vol. . - b. 48 0.20 48 0.10 48 0.10
BACTERIA
ODOR
12,000 8,000 7,800
Fermentative Fermentative Fermentative
Sucrose Dextrose Levulose
72 72 72
0.45 0.25 0.25
980,000 210,000 200,000
Fermentative Fermentative Fermentative
Sucrose Dextrose Levulose
96 96 96
0.80 0.50 0.48
28,800,000 1,600,000 1,800,000
Putrid Fermentative Fermentative
Sucrose Dextrose Levu 1ose
120 120 120
0.80
1.05
No count 24,000,000 26,000,000
Putrid Putrid Putrid
0.75
The results indicat that th dextrose- and levulose-treated batters resist fermentation and bacterial decomposition more vigorously than do those to which sucrose is added. It is thought that these differences are due to the greater osmotic pressures developed by the monosaccharides, the osmotic pressure of the dextrose solution being 1.75 times greater than that of a sucrose solution of equal concentration. Conclusions
The white portion of eggs suffers no breakdown as the result of freezing. The physical character of the yolk portion is altered on freezing, owing to the separation and coagulation of the lecithin. The coagulation of the lecithin may be prevented by the addition of 10 per cent by weight of dextrose or levulose, either of which is a much more effective anti-coagulant than sucrose. None of these sugars form permanent combinations with the egg materials or lecithin during the freezing. The watery and ropy condition of thawed yolks may be eliminated if the yolks are frozen with dextrose or levulose and to a lesser extent with sucrose. From the standpoint of the prevention of the fermentation and bacterial decomposition of the thawed batters, dextrose or levulose is much more effective than sucrose. Literature Cited (1) Plimmer, "Practical Organic and Bio-Chemistry," pp. 175, 176, and 463.
Purification of Normal Paraffin Hydrocarbons b y Chlorosulfonic Acid Treatment' Alvin F. Shepard and Albert L. Henne CHEMISTRY DEPARTMENT, THE OHIO STATE UNIVERSITY, COLUMBUS, OHIO
H E preparation of pure hydrocarbon samples from petroleum by fractional distillation is generally considered an impractical task. Young (6) isolated pure n-pentane, but was unable to purify its higher homologs completely by distillation. No other liquid normal paraffin hydrocarbon, except hexane (6), has ever been isolated in a state of purity from such a source by any method. Fractional distillation will separate a normal paraffin hydrocarbon from most of its isomers; the sample thus obtained may boil over a very narrow range, but its density will be much higher than that of synthetic preparations (2). The presence of naphthenic hydrtrcarbons has been demonstmted and the existence of azeotropic mixtures suggested but never proved.
T
1
Received January 27, 1930.
The writers have studied several chemical methods of' purification, but have obtained satisfactory results only by treatment with chlorosulfonic acid. The principle of. the method is due to Aschan (1) and has been emphasized by Young (?). They have shown that hydrocarbons (naphthenic as well as paraffinic) containing a tertiary carbon atom are rapidly attacked, whereas the normal paraffin hydrocarbons and cyclohexane are only slowly affected. This method has consequently been used to remove hydrocarbons with side chains. Fractional distillation has been employed to eliminate cyclohexane and cyclopentane. Large samples of each normal hydrocarbon from hexane to dodecane have been prepared. Their physical properties compare favorably with those of the best synthetic prepara-
