AUGUST, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
ness (independent of water and protein content) has less than a clearly significant value emphasizes the relative unimportance of shell thickness as a factor in light transmission. The visibility of the yolk shadow in commercial grading of eggs by candling will depend on any property of the shell
973
which can control the direct passage of light through it. Such properties are the water content and the protein content of the shell, which, so far as present knowledge indicates, are independent of the true internal quality of eggs. RECEIVED
Jlarch
1935,
0
.*((I
#)t.
Foaming of Egg White 31. IRESE BAILEY
Columbia University, New York, N. Y.
*+((I
P
U B L I S H E D reports of quantitatively controlled experiments on the whipping of egg whites are few. Of two previously published articles, one gives results based on the use of a slotted-disk, handoperated beater ( 5 )while the results in the other report were obtained by means of a motordriven Dover type of beater (1). I n this investigation a different type of motor-driven beater was e m p l o y e d , yielding results in certain r e s p e c t s c o n t r a r y t o those published. One feature of the present i n v e s t i g a t i o n is that i t d e a l s w i t h m i x e d specimens of 70 to 220 pounds (31.8to 99.8 kg.) of egg white, t h u s e l i m i n a t i n g individual variations in eggs.
A new method for the determination of the foaming power of egg white and for testing the stability of the foam obtained has been developed. Unfrozen whites and thawed whites after frozen storage for short periods of time showed no pronounced difference in foaming power. Thick white had a higher foaming power (using the method described in this paper) than the thin white. Untreated egg white possessed a higher foaming power than did any of the treated egg-white mixtures tested (pH 5 , 6, 7, or 9.5). The addition of olive oil to egg white produced a greater decrease in foaming power than could be accounted for by the addition of the same amount of fat in the form of egg yolk. The stability of the foam varied with the treatment and the type of egg white used.
Procedure The Hobart C-10 mixer,‘ with an adapter which allowed for the use of a 3-quart (2.8-liter) bowl, was selected for the determination of the whipping power of egg whites. The regular Hobart wire whipper was used. The highest speed (No. 3) was found most satisfactory and was adopted for all experiments, the motor revolving a t a rate of 2300 r. p. m. The rotating whipper, eccentrically situated on a rotating disk, described a hypocycloid path; the rotation of the beater on its axis was 604 r. p. m., that of the rotating disk was 255 r. p. m. The axis of rotation of the whipper was 2.5 cm. from the axis of rotation of its supporting disk. One hundred and fift grams of the uniform mixture of egg white were placed in t i e 3-quart bowl of the Hobart mixer, the white was adjusted to room temperature to avoid large changes of temperature during whipping, the whipper was adjusted in place, and the machine was started. At the end of the desired time interval, measured by a stop watch, the machine was stopped. Immediately, a crystallizing dish [313/,0 inches (9.7 cm.) in diameter and 2 inches (5.1 cm.) in height] was fitled with the whipped white, the top of the extruding foam being leveled off by means of a straight edge. (The excess of whipped white in the beater bowl was discarded. For each time of whipping, a new specimen of egg white was used.) The crystallizing dish and its contents were then weighed to an accuracy of 0.5 gram in order to obtain the weight of the foam or ‘‘whipped 1
Manufactured b y the Hobart Manufacturing Company, Troy, Ohio.
white.” This value was used to calculate the foaming power by means of the formula: F =
(+
100
) - 100
whereF = foaming power of egg white V = volume of dish, cc. W = weight of foam, grams
The specific gravity of egg white was taken as 1.04. The following procedure was adopted as a m e a s u r e of the s t a b i l i t y of the foam: After weighing the crystallizing dish with its contained foam, it was allowed to stand at 2 5 O C . for one h o u r , c o v e r e d by an inverted can [41/4inches (10.8cm.) in d i a m e t e r and 5 1 / s inches (14.9 cm.) in height] to inhibit evaporation. A t the end of one hour the volume of the liquid white that had “leaked” (separated owing to collapse of the foam) was measured. The percentage of leakage, L , was calculated by t h e formula:
L
1041 = -100
W where 1 = volume of leaked egg white, cc. The whipping times were generally 3, 6, 9, 12, 15, and 18 minutes. The foaming powers, F , and the per cent leakage, L , were plotted as ordinates against time in minutes as abscissas. From experience with 150 measurements it was found t h a t the weight of the whipped whites in the crystallizing dishes could be checked within h0.5 gram in 80 per cent of the cases, while 90 per cent checked * 1.0 gram or less. The greatest variation was k3.0 grams in two cases, both of which were 3-minute whips. Frequently, the foam a t the end of the 3minute whip was dry and for this reason i t wad difficult, if not impossible, t o fill the measuring dish free from voids.
Influence of Type of Whipper When this investigation was started, 8 motor-driven Dover beater was used. The twin beaters rotated a t 1035 r. p. m.,
VOL. 27, NO. 8
INDUSTRIAL AND ENGINEERING CHEMISTRY
914
actuated by a Bodine motor (8800 r. p a m.) through a speedreduction gear. This type of beater was found to be unsuitable for quantitative studies of the foaming power of egg white because the whipped white, by virtue of its stiffness, soon became immobilized around the beaters with the result that the blades rotated in a central cavity. Attempts to push the surrounding wall of whipped white back on the beater blades proved futile from a quantitative point of view. A specimen of egg white which attained a maximum foaming power of 1190 in the Hobart machine showed a maximum foaming power of only 420 in the motor-driven Dover beater. The Dover-whipped egg white was less stable as shown in
,
1200
I
I
3
180
I
I
I
1
6
9
,2
/I
I8
7;me o f Whip in Minutes
FIGURE1. CO~MPARISON OF HYPOCYCLOID WHIPPER MOTION AND ROTATION OF W-HIPPER ABOUT STATIONARY AXIS H = Hobart mixer: D = Motor-driven Dover beater.
Figure 1. Obviously, a hypocycloid whipping action is required for measurements of the whipping qualities of eggwhite specimens. For this reason the Hobart whipping machine was adopted.
TABLEI. ANALYTICAL DATAON EGGWHITESBY METHOD OF THOMAS AND BAILEY (6) SDecimen
DH
8/23/32 9/27/32 10/25/32 11/10/32 11/15/32 11/29/32 12/13/32 1/10/33 2/ 7/33
8.73 8.66 8.43 8.68 8.75 8.85 8.70 8.70 8.97
Flow Time, Seo.
Total Solids, To ,12.87 12.75 13.50 13.28 13.24 12.89 13.70 13.49 12.40
35.8 32.1 36.6 32.1 31.6 31.0 33.2 31.7 32.6
It is apparent that there was no pronounced difference in the foaming power of the unfrozen and the thawed frozen egg white except for a tendency of the thawed frozen whites to reach a maximum increase in volume in a shorter time of whipping than the unfrozen whites. However, t h e percentage of leakage varied. The leakage of the foams from the thawed frozen specimens was greater than that from the unfrozen whites, but the sharp changes in leakage as a result of varying whipping times, observed in the case of the unfrozen specimens, did not occur. It is interesting to note that the optimum whipping time for minimum leakage is usually a little less than the whipping time for the maximum foaming. This effect was not always obtained, but its appearance in the majority of the cases for unfrozen egg white or for egg white kept in frozen storage for short periods2 would justify the 2 I n the case of egg white kept in frozen storage from 3 to 4 months the general tendency is for this minimum in leakage to become less sharp or in some casea to disappear completely.
1
I
Influence of Time of Standing Prior to Whipping I n order to determine the effect of time of standing of the specimens upon subsequent foaming power, 15 pounds (6.8 kg.) of freshly broken out egg white were mixed by means of slowly rotating Dover blades, placed in quart jars, and sealed. Foaming ower determinations were made immediately upon some of the geshlg churned egg-white mixture. The remainder of the egg white was stored at 3" =t1' C. On the following morning, part of the white was tested to see if standing at this temperature for 18 hours affected the foaming power. Another portion was allowed to stand in uncovered, shallow glass dishes for 7 hours at room temperature (25" =tl o C.) and then tested for whipping quality.
I
1
'
I
While the whites exposed in the shallow dishes showed a slightly smaller increase in volume upon whipping, there was no significant difference in the volume of the whites tested immediately and those kept in sealed containers a t 3' * 1' C. Measurements made several hours apart are therefore comparable.
Comparison of Unfrozen and Frozen Whites For the purpose of comparing the foaming power of unfrozen egg whites and that of the identical egg-white mixtures thawed after a short period in frozen storage, nine specimens of egg white were prepared on different days (Table I). Portions varying from 70 to 220 pounds (31.8 to 99.8 kg.) of freshly broken out egg whites were churned in a commercial egg churn from 10 to 24 seconds in order to tear and mix the "thick" and "thin" portions of the whites so that the entire mixture would be uniform. Samples of the churned whites were tested in order t o determine the foaming power of the unfrozen white. The remainder of the egg-white mixture was immediately stored in 2-pound (0.9-kg.) cans in a "sharp freezer" at -5' to 0" F. (-21' to -18" C.). After certain intervals in frozen storage, specimens were removed in order t o determine the foamin power and the leakage of the thawed frozen whites. Typica? curves are shown in Figure 2.
1
I
I
I
I
6
9
/P
/5
18
7ime of W h p / n Minutes
FIGURE2.
COMPARISON OF UNFROZEN FROZEN EGGWHITE
.4ND
Upper graph: 9/27/32 specimen; U = unfrozen white. F = white frozen 177 days. cedter graph: IO 25/32 specimen: u = unfrozen white; F1 = white kozen 9 days; Fs = white frozen 153 days. Lower graph: 11/10/32 a ecimen; U = unfrozen white; F I = white frozen 7 rfays; F; = white frozen 140 days.
AUGUST, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
above statement. Therefore, if stability of foam is desired, the egg white should not be whipped to its maximum degree of foaming.
Comparison of Thick and Thin Whites Using the method of and the screen proposed by Holst and Almquist (S), seventeen egg whites were separated into thick and thin portions. It was found that, when foaming power measurements were made with a Dover type machine, the thin white gave a higher lifting power than did the thick portion, which is in agreement with the work published by St. John and Flor ( 5 ) . This occurrence is probably due to the fact that the thin white continued t o fall back on the Dover beater blades while the thick white was soon immobilized as previously mentioned for whole whites. Different results were obtained when a Hobart machine was used. While the Holst and Almquist hand screen is serviceable for separating individual whites, it was essential to devise a larger apparatus for the quantity production required in this investigation: A long trough made of sheet metal perforated exactly according to the specification of Holst and Almquist was used for the separation. The egg whites were allowed to slide back and forth so that the thin portion ran through the perforations while the thick white remained on top. This apparatus showed that the se aration of egg whites into thick and thin portions may be variezat will. The slower the whites slide over the inclined perforated metal and the higher the pressure (the greater the amount on the screen), the greater is the yield of thin white. On three different days three distinct specimens were prepared. Portions of 70 to 94 pounds (31.8 to 42.6 kg.) of egg whites were allowed to run slowly down the inclined perforated trough previously described, the thick and thin whites being collected in separate large containers. I n order to form a uniform mass of the contents of these containers, a disk with one-inch (2.5-cm.) circular perforations was pushed slowly up and down through the whites. Then the mixed specimens were placed in 2-pound (0.9-kg.) cans. Except for the samples of unfrozen thick and thin whites which were taken for immediate analysis and foaming power measurements, the cans were placed in frozen storage at -5' t o 0' F. (-21' to -18' C.). The proportions of thick and of thin white obtained are recorded in Table 11. The percentage of total solids in the thick and thin white was practically the same. This is in agreement with the data published by Holst and Almquist ( 2 ) on the total solid content of thick and thin white specimens separated from individual eggs.
TABLE11. ANALYTICALDATAON PROPORTIOXS OF THICKAND THIN WHITE OBTAISED
a
ProporSpecimen Portion tion, % pH 37 8.85 8/11/32 'Thick Thin 63 8.82 33 8.79 8/16/32 Thick 67 8.74 'Thin 64 8.71 9/14/32 Thick Thin 36 8.69 Not a n even flow, therefore not precise.
Total Solids, Flow Time, % See. 12.60 156a 12.56 30.6 262a 13.20 13.31 36.9 12.31 Y 12.60 29.7
T h e thick and thin whites behaved differently when whipped in the Hobart machine as shown in Figure 3. A greater volume of foam was obtained with the thick whites. These results do not agree with those of St. John and Flor ( 5 ) nor with those of Henry and Barbour ( I ) who reported the reverse effects. As previously stated, this difference is due to the nature of their whipping machines. Inasmuch as some practical workers on egg white have the impression that breaking u p the structure of the whites impairs their foaming power (i. e., that the author's process of preparing a large uniform sample by churning impaired the foaming property of thick white), the following experiment was performed : Part of one sample of thick white was whipped as separated, while another portion was mixed until the struc-
975
ture disappeared and was then whipped. The mixed structureless specimen gave essentially the same foaming power curve as the unbroken whites. Hence the results above described cannot be ascribed to the author's method of preparing large, uniform specimens. It is not known why the thick white had a higher foaming poFer than the thin white, although i t may be possible
Erne o f Whhip in M l n u f e ~
FIGURE 3. BEHAVIOR OF THICKAND THIN WHITE
-
Upper graph: 8/16/32 specimen (not frozen); = thick white; N thin white. Lower graph:. 9/14/32 specimen' K U = unfrozen thick white. N U = unfrozin thin white; KF, thick whitd froeen 23 days; NF thin white frozen 23 days.
K
-
-
that the mucin content has some bearing upon the subject. McNally has reported recently ( 4 ) that the thick portion contains a much higher proportion of mucin than does the thin white. The leakage of the thick portion increased with increasing time of whip, while the leakage for the thin decreased with increasing time of whip. However, for the short time of whip (3 to 9 minutes) the leakage of the thin white was always greater than that of the thick portion for the same time of whip. After the 12-minute whip the thick white had a higher percentage of leakage.
Effect of pH In order to determine the effect of hydrogen-ion activity upon the foaming power of egg white, three distinct series of specimens were prepared in which the pH was varied from 9.5 to 5. With each series a natural, unaltered egg white was used for comparison. In the preparation of the specimens a uniform sample was first obtained by churning 100 pounds (45.3 kg ) of freshly separated egg whites. This uniform mixture was divided into three or more portions as desired. One portion was left untreated (W). To another portion enough phosphoric acid (85 per cent) was added to adjust the pH t o 7 (W7). To a third portion phosphoric acid was added in such amounts as to give pH 6 (W6). In one case a specimen at pH 5 (W5) was also prepared. In two instances pH 9.5 (W9.5) was obtained by the addition of anhydrous sodium carbonate. Whenever a reagent was used, it was added slowly while the egg-white mixture was being poured from one container to another, and the contents TTere thoroughly mixed by continued transfer from one 30-pound (13.6-kg.) can to another. Unfrozen specimens of each were immediately analyzed and subjected to foaming-power measurements. The remainder of the egg-white mixtures was placed in 2-pound cans and stored at -5' to 0" F. (-21' to -18' C.). Such specimens were prepared on June 23, 1932, January 10, 1933, and February 7, 1933. The egg whites used in January were from storage eggs while those frozen in June and February &-erewhites from fresh shell eggs. Analytical data on the three ex eriments are given in Table 111. The pH values were determinezby a modified C. H. Bailey electrode cell as previously described (6). This closed type of electrode is required on account of the carbon dioxide present in egg white.
INDUSTRIAL AND ENGINEERING CHEMISTRY
916
I n regard to foaming power the untreated egg white lifted better than did any of the treated egg-white mixtures (TV9.5, W7, W6, and W5). I n all cases the thawed frozen treated specimens had lower maximum foaming powers than did the corresponding identical unfrozen samples. The treated specimens in frozen storage for 4 months had a lower maximum foaming power than similar ones had shown after 1 month in frozen storage.
VOL. 27, NO. 8
To 150 grams of egg white, portions of 0 to 1.0 per cent yolk were added and the foaming power was determined, using a 6minute whip. The foaming power of the whites was seriously impaired by even a small amount of added yolk. The stability of the foam was slightly increased by the addition of yolk. When a 9-minute whip was used, higher foaming powers were obtained but the general shape of the curve was the same as for the 6-minute whip.
This experiment was repeated using uniform mixtures of egg white and yolk prepared as previously described. Analyses of these mixtures gave the following results (in per cent) : Yolks
Whites 12,59 0.00
Total solids Ether extract (Soxhlet)
50.31 30.15
It is known that added yolk diminishes the foaming power of egg white. I n order to ascertain whether the decreased foaming power was a function only of the fat content of the added yolk, small amounts of olive oil were added just before whipping to portions of egg white identical to those used when yolk was added. Figure 5 shows that, when olive oil was added to egg white, a greater decrease in foaming power and a larger increase in leakage occurred than was observed in
~3
9
6
12
I5
/a
Time o f Whip in Minutes
FIGURE4. EFFECT OF HYDROGEN-IOX ACTIVITYON SPECIMEN FROZEN 9 DAYS (1/10/33) W = untreated white: 73'9.5 = PH 9.51; W7 p H 6.80;
W6
= p H 5.97: W5 = pH 4.93.
=
om
c.m
030
0.w
am
Grams of O i l Added
While the untreated egg white possessed higher foaming power than did the treated specimens, the foam of the eggwhite mixture adjusted to p H 7 or 6 was, for the most part, more stable than the foam of the whipped untreated egg white. The white adjusted to p H 5 is of interest because, while it took 15 to 18 minutes of whipping to produce a decided increase in volume of the foam, on the other hand, the leakage diminished markedly (Figure 4). Consequently, if one desires a very stable foam, it may be obtained by prolonged whipping of egg vhite adjusted to p H 5 . TABLE 111. EFFECT OF PH ON FOAMING POWER SDeoimen 6/23/32 W w7 W6 1/10/33 W w9.5 W7 W6 w5 2/7/33 w9.5 w7 W6
w
DH 8:73 6.84 6.12 8.70 9.51 6.80 5.97 4.93 8.97 9.60 7.07 6.19
Total Solids, ?A ._ 12.87 13.49
12.40
Flow Time,
FIGURE 5 . EFFECTOF ADDEDYOLK.IUD OIL Y
=
yolk: 0
=
OF
olive oil.
the case of the addition of the same amounts of fat in the form of yolk. Obviously, either olive oil inhibits foaming power to a greater extent than yolk oil, or, on the assumption that the two oils have equal effect, then other substances in yolk counteract the foam inhibitory effect of the yolk oil.
Acknowledgment The author is indebted to the Borden Research Foundation for its grant-in-aid and expresses her appreciation of the advice offered by M. E. Pennington.
Sea.
35.8 30.1 22.4 31.7 30.7 29.5 22.0 20.5 32.5 32.2 29.7 21.5
Literature Cited (1) Henry, W.C.,and Barbour, A. D.,IND. ENG.CHEM.,25, 1054 (1933). (2) Holst, 1 5'. F., and Almquist, H. J.,Hilgardia, 6 , 4 5 (1931). (3) Ibid., 6,49 (1931). (4) McKally, E.,Proc. SOC.Ezptl. Biol. M e d . , 30, 1254 (1933). (5) S t . John, J. L., and Flor, I. H., Poultry Sci., 10, 7 1 (1931). (6) Thomas, A. R., a n d Bailey, M. I., IND. ESG. CHEM.,25, 669 (1933). R E C E I V EFebruary D 11, 1935. Thie investigation was carried out under the direction of Arthur UT.Thomas, Chemistry Department, Columbia
Effect of Added Yolk and Oil
University.
A uniform mixture of egg white from storage eggs was obtained by churning 5 pounds (2.3 kg.) of whites in a laboratory
mixer. Twelve yolks mere separated from shell eggs and uniformly mixed. These two mixtures had the following percentage composition: Total solids Ether extract (Soxhlet)
Whites 14.10 0.08
Yolka 46.05 26.55
International Citric Acid Agreement. According to the monthly bulletin of the Banco di Sicilia, the international citric acid agreement signed last year is to last five years. The Italian industry is to be assigned a quota of 38 per cent of total sales of the signatories to the agreement. It was also agreed to keep the price between a minimum of 4.20 lire and a maximum of 5 lire.
