MARCH, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
most stable at the neutral point. However, dispersions can be prepared with pH values as low as 5.7. Low temperatures also favor stability of the sol. Higher concentrations of the protein-formaldehyde dispersions are made possible by a mild hydrolytic treatment of the protein with alkali or by the action of souring bacteria or yeast on the water dispersion of the protein.
Literature Cited (1)
Brother, G. H., and McKinney, L. L., IND. E m . CHEM., 30,1236-
40 (1938). 1 (2) Chibnall, A. C., Bailey, Kenneth, and Astbury, W. T., British Patent 467,704 (June 22, 1937).
(3)
415
Cone, C. N., and Brown, E. D., U. S. Patent 2,006,229 (June 25, 1935).
(4) Ferretti, A., British Patent 483,868 (April 21, 1938). ( 5 ) Gortner, R. A., "Outlines of Biochemistry", Chap. IX, New York, John Wiley & Sons, 1938.
Horvath, A. A., U. S.Patent 2,045,468 (June 23, 1936). (7) Laucks, I. F., I b i d . , 1,942,109 (Jan. 2, 1934). (8) Satow, Sadakichi, Ibid., 1,280,862 (Oct. 8, 1918).
(6)
(9) Satow, Sadakichi, Tech. Repts. Tbhoku Imp. Univ., 3, No. 4, 21 (1921). (10) Satow, Teikichi, U. S. Patent 1,824,448 (Sept. 22, 1930). (11) Smith, A. K., and Circle, S.J., ISD. ENG.CEEM.,30, 1414-18 (1938). (12) Ibid., 31, 1284-8 (1939). (13) Smith, A. K., Max, H. J., and Handler, P., J . Phys. Chem., 43, 347-57 (1939).
Effect of Air Film in Emulsification HE purpose of this investi-
EMULSION Ia. The same proIRENE SANBORN HALL' AND cedure as for emulsion I is folgation concerning the staELSIE HALSTROM DAWSONZ lowed, except that all nil is inbility and homogeneity of jected beneath the surface of the University of California, Berkeley, Calif. oil-in-water emulsions of highemulsion. oil content has been twofold-to EMULSION 11. To 20 grams of egg yolk 34 grams of vinegttr and compare emulsions made by two 7 grams of spices are added. Oil methods differing only in the The stability and homogeneity of oil-inis then dropped from a point 6 time and manner of adding the inches above the forming emulsion water emulsions of high-oil content have oil, and to study the effect of an at the rate of 0.4 cc. per second. been found to be less when an air film adThe beater is operated at 950 air film on the oil constituent. r. p. m. throughout the emulsiheres to the oil phase than when such a Factors which affect stability, fying process. such as temperature, storage, film is absent. This is true in both of the EMULSION IIa. The same prorate and type of agitation, nature cedure as for emulsion I1 is foltwo common methods of emulsification and concentration of ingredients, lowed, except that all oil is injected studied. The emulsions are of the mayonbeneath the surface of the emuland kind and size of equipment, sion. naise variety, made according to a formula have been kept constant similar to that used by the mayonnaise throughout experimentation. The temperature while the Two methods, American and manufacturers with the exceptions that the preparations were being made compromise are used. In the egg yolk emulsifier is fresh, and that exmas controlled within 2" (20American method the emulsiceedingly large quantities of oil are emulsi22" C.) by a stream of cold fying agent and acid are comfied by very small amounts of yolk. water impinging upon the side bined a n d t h e oil i s a d d e d gradually. I n the compromise of the rotating bowl. Figure 1 shows the emulsifying apparatus. method, a cross between the American and Continental methods, the emulsifying agent The following ingredients were used: is combined with a small portion of the oil, the acid is introOIL. Sesame oil, a salad oil of pleasant nutty flavor, had the duced and the remainder of the oil is added gradually. Each following chemical and physical constants: of these methods is carried out under two conditions: (a) Speaifia gravity at 4 O C. 0.917 Refractive index at 22' C. 1.475 where all the oil is introduced beneath the surface of the 59.26 Viscosjty (Stbrmer) at 20' C., centipoises emulsion, and (b) where all the oil is dropped into the emulSaponification number 194.5 Iodine number (Hanus) 106 sion from a point 6 inches (15.2 cm.) above the emulsion 1.82 Reiohert-Meissl number surface. For convenience these four emulsions are desigEMULSIFYING AGENTS. Fresh egg yolk (not more than 24 nated as follows: (I) compromise-above, (Ia) compromisehours old) was used. Each egg was submitted to the brine test, beneath, (11) American-above, (IIa) American-beneath. and after separation from the white, the yolk was rolled on cheese cloth to free i t from any adhering albumin. The pH (quinhydrone electrode) of such yolks varied from 6.36 to 6.48 Preparations a t 20" C. Yolks for comparable preparations were pooled and mixed slightly with a glass rod. EMULSION I. To 20 grams of egg yo& prebeaten for 30 secSucrose c. P . , sodium chloride c. P., dry mustard, and paprika onds, 30 t o 35 grams of oil are added in a continuous stream from a were combined by thorough mixing in a mortar and pestle in point 6 inches above the emulsion surface, at the rate of 0.1 cc. sufficient quantities to provide for all preparations, and weighed per second with agitation of 650 r. p. m. This mixture is very portions were used as needed. stiff, and since any further addition of oil will cause breaking, ACID-WATER.Vinegar used was found by standard methods this point is considered optimum dispersion (0. D.). To this to contain 1.92 per cent solids and 5.22 per cent acid as acetic; mixture 34 grams of vinegar and 7 grams of mixed spices are it had a pH of 3.30 at 20" C. added, with the result that the emulsion is thinned without being broken. The remainder of the oil is then added a t the All emulsions mere studied from two points of view-their rate of 0.4 cc. per second until the desired concentration is atbehavior'during formation and their properties. Stable emultained. The speed of the beater is increased to 950 r. p. m. upon the addition of the vinegar. sions containing 89-93 per cent oil were prepared. Table I shows t'heir compositions. The figures and illustrations of 1 Present addresa. Western Reserve TJniversity, Cleveland, Ohio. ' Present address, Syracuse University, Syracuse, N. Y. emulsions in this article are for the 92.91 pet cent oil series.
T
'
In-DUSTRIAL AND ENGINEERING CHEMISTRY
416
y. M is the mean value. Values for a and b were found by the following:
TABLEI. COMPOSITION OF EMULSIONS STUDIED Sesame oil Egg yolk
Vinegar Solids Water Acid Total spice Sucrose Sodium chloride Mustard Paprika
Components, Grams Variable 20.0 34.0
VOL. 32, NO. 3
C 0 m p n . F 500 g. oil 89.12 3.56
7 %
0.6
33.4
1.8
7.0
4.5
1.4 0.7 0.4
800 g. oil 92.91 2.32 3.94 0.8 3.87 0.21 0.81 0.52
6.06
a = My
0.12 5.94 0.31
- bXx
The equation for the straight line was therefore:
1.25
0.80 0.24 0.12 0.07
0.16
0.8 0.05
y = a f b x
The points of the curves for the compromise emulsions (I and Ia), marked 0. D., indicate optimum dispersion; points where maximum thickness is attained and any further addiEffects of Storage tion of oil will cause the irrecoverable breaking of the emulsions. The addition of acid a t this time thins the emulsions Six-ounce samples of the emulsions were stored in widewhich are subsequently rethickened by more oil. Even mouthed tightly covered glass jars a t 8" and 22-25" C. though points 0. D. in emulsions I and I a represent mixtures (room temperature). Samples were examined from time to of the same composition, they are in quite different positions. time over a period of 2 years. At the end of this time the Point 0. D. of emulsion Ia represents a much stiffer mixture emulsions appeared as follows: than 0. D. of emulsion I. R. p. m. decreases and amperage increases as the emulsions thicken. The slopes of curves I a I Fragile and partly separated and IIa are greater than those for I and 11, respectively, and Ia No separation more time is required for oil emulsification when the oil is I1 Complete separation injected beneath the surface. The lowest r. p. m. readings a t IIa No visible separation, b u t very fragile-i. e., separates after stirring for a few minutes the end of the preparations are invariably those of the compromise (I and Ia) emulsions, and emulsion Ia always has the thicker consistency of the two and therefore the lower Table I1 compares storage behavior during 2 years. The comr. p. m. The curves for American emulsions (I1 and IIa), promise-beneath (Ia) emulsions, those rating best a t the 8' C. like the latter segments of I and Ia, indicate the increase of storage temperature, were broken m-ithin 8 months when consistency as the emulsions near completion. The true stored a t room temperature. The other three emulsions had significance of these curves as mathematical exmessions of broken several months earlier under the latter conditions. consistency measurements has not been determined. Extensive data are available, and further analysis should yield fruitful results. TABLE 11. MACROSCOPIC OBSERVATIONS OF EMULSIONS STORED AT 8" C. Approx. Age. Weeks
I1
Method IIa
Very stiff, stable
Stable, thick
Stable, thick
Stable, thick
Very stiff, stable
Stable
Stable
Stable, thick
Stable
Stable
Stable
Stable, stiff
Stable, stiff, not so high consistency as a t 24 weeks
Stable, thin
Stable
Stable, a little fragile
Thin, slightly broken appearance
Method I
Method I a
11
High consistency
17 24 48
Method
Specific Gravity and pH Emulsions I and I1 have lower specific gravities than Ia and IIa, respectively: Emulsion
(Age 24 Hr.)
I Ia I1
IIa
AY. Sp. Gr.
at 22'/4' C . 0.887 0.918 0.917 0.927
The adsorption of air by the oil as it drops the 6inch distance is thought to cause an emulsification of both air and oil, and thus accounts for the lower specific gravities of these emulsions. Considerable Thin and 75 Fragile, sepaNo separation, During the first 3 months of storage a slight deseparation, runny, still rating very fragile crease in pH occurs in all of the emulsions (Table emulsified emulsified p a r t fragile V). This initial decrease is followed by an increase as the emulsion continues to age. These changes Complete No visible 104 Fragile, parVery fragile separation separation, tially sepaalthough not may be explained in part by the changes occurfragile rated separated ring in the egg yolk. I n addition to the yolk prointo two teins, egg yolk contains lipoidal compounds, inphases cluding lecithin and cephalin, both of which are readily oxidized by air. SIitchell (4) believes that the decomposition of lecithin in eggs is due Behavior during Formation to bacterial action which-results in the formation of fatty acids and the disappearance of lipoid phosphorus and choline The behavior of the emulsions during preparation was nitrogen, Perlman (5) attributes the actual decomposition studied by means of r. p. m. v s . ampere records. Table 111 of the lecithin to enzymes produced during the growth of shows four typical runs. These data are depicted graphically the bacteria. Such decomposition will cause a n increase in by Figure 2. R. p. m. us. ampere data were analyzed by the method of least squares so that a straight line resulted for pH. The hydrogen ions retard these changes by combining with the yolk proteins to produce a soluble acid protein which each emulsion. All ampere and r. p. m. readings were used. serves efficiently as a buffer for a time. After 2 years the pH In Table IT: amperes are represented by z and r. p. m. by 61
Stable, thin
Fragile
MANCH. 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
TARLE111. EMULSIFICATION PnoCESS WITK n. AMPEREREcoRns AT 20-24' C." Tima
--Method
Mi*.
Amp.
1 2 3. 4
0.241 0.240 0.235
0.245 0.245 0.248 0.248 0.255
5
2
i
!I 10 11
12 13 14 15 16 17 18 19 20 21
625
625 605 605 1000b 985 995 975
0.265
0.4208 0.410 0.415 0.428 0.442 0.450 0.442
865
925 880 880
0.445
n ,460
880
0.495 0.512 0.620 0.5411
850
860
0.490
22
23 24 25 26 27 28 29 30
IR . p . m, 630 635 625 630 630
0.545
n.500 0.535 0.580
... ... ... ...
a1
Amp. 0.200
0.199
0.190 0.189
0.190 0.191 0.190
0.195 0.201 0.250
0.315b 0.340 0.349 0.352 0.360 0.380
0.364 0.365 0.380 0.385 0 ,890 0.402 0 ,405 0.418 0.418 0.425 0.440 0 ,445
... ... ... ...
0.450
...
-Method
IaR. P. m 620 615 630 615 620 615 620 600 600 595 960k 910 910 920 e10 900 890
Amp.
860 850 850
s40 820
n . 5%
810
0.6%
945 945 948 970 950 945
885
865 860 860 855 845 825 815
800
795 795
785 796
... ... ... ... ... ... ... ... ...
...
...
... ... ... ... ...
750
750
... ... ...
~
~
AND
-Method Amp. 0.385 0.385 0.388 0.388
0.392 0.395 0.395 0.408 0.422 0.428 0.428 0.428 0.428 0.430 0.435 0.445 0.450 0.452 0.455 0.458 0.460 0.460 0.462 0.465 0.475 0.4w 0.485 0.490 0.490 0.488
950 940 920 910
... ...
pb.
0.400
950
0.535
790 780 7?5 760
... ...
IlR . p . rn
0.415 0.415 0.420 0.405 0.420 0.430 0.435 0.440 0.450 0.455 0.458 0.475 0.485 0.490 0,505 0.505 0.610 0.612 0.510 0.530 0.530
585
0.300
835 805 795 785 780 770 7F5 750
0.555
-Method
P.
e.
11sP. m. 890 950 950 950 940 940 945
945 945 928
925 910
905
no0
880 885 870 865
862 860
855
850 845 835
825 815 8zO 815
sns
8011 19s
795 795
0.490 0.490
_
417
FIGERE 1. EMUISIPYIXG APpAnnTUs Hamilton Beech mixer, milliammeter, tachometer, and Standard electric stop watch.
_
ANALYSISOF DATAON EMULEIFICATION PAOCESS (TABLE 111) BY METHOD 01 LEAST SQUARES
TAHLE IV. Method I
"
S
'roo. n. IO 2.487 1 I e ~ o n d O . D . 19 9.204 Method la T O O . n. 11 2.185 ~ e ~ ~ r ~ 1 0 23 . 1 1 .8.878 Method I1 24 11.400 Method IIa 33 14.540
u
s
ZY
Mz
My
6210 0 . ~ 1 9 1543.41 0.249 621 16460 4.512 7896.24 0.484 868
6765 0.437 19x80 3.455 21168 5.462 288Y2 6.449
1342.39 7490.62 9988.04 12667.88
D
897 1427
0.190 616 1120 0.386 84s 1503 0.475 881 m 9 0.441 875 1476.5
of the fragile breaking emulsions approachcs the imelectric point of the p r o t e i livetin (4.8 to 5.0), and this may explain the appearance of a flaky precipitate at the time the einulsion breaks. Invcrsely, this may be considered as one of the factors in the breaking of the etnulsions. All such pll changes arc effectively retarded b y storage c!mditions at 8" C. The entire range of pI1 fluctuation is small, a fact which helps to explain the high stability of the emulsions. TABLE V. Method
la
CHANGES IN Expt.
1
2
3 4 11
1 2
11%
1 2
3 4
P n DURING
--110~.5 -1158.6 -2536 -1894 -1341 -1364
coiisistency determinations was so great, the character of the emulsions changed so much during a single determination, and the size of the sample required was so large that the instrument eventually gave way ti) the peut,rameter, an instrument devised in this laboratory (Figure 3).
The pentrmieter consists of a solid synthetic amher plummet, 16.5 em. in length and 1.5 cm. in diameter, which slants off t o a point 0.8 cm. from the end. The lummet is fastened to a metal rod, 21.2 em. in length %n$O.B cm. in diameter, equipped with B small ointor near the top to indicate on tho centimeter scale parallef to the rod the distance that the instrument penetrates the emulsion. This rod is mpportcd by a spring clamp whioh, when released, allows the plummet to drop perpcndicular to tho
AGINGOF EMULSIONS
I Hr.
3-6 Mu.
After
After 12-16 &to.
4.29 4.44 4.2G 4.42
4.24 4.32 4.21
4.25 4.44 4.36
4.36 4.52 4.48 4.68 4.55 4.57
4.30
4.44
After
b
4.18
4.44 4.18 4.39 4.44 4.40
4.53
...
6.74
5
......
4.43
...
...
Consistency in the Pcntrameter httcrnpts 71-ere made to conduct. t.his study by means of the Gmlner-I'arks mohilorneter (8). Tlie time required for
e
"a
80
a4
a5
AM%
AM FI
FrGrJnE2. PREP*RATION
CURVE8
Many points repent themselves.
418
INDUSTRIAL AND ENGINEERING CHEMISTRY
pendicular fail of the instrument. Consistency readinrs with the electricstopwatch were m a d e i n seconds-i. e., the time required to penetrate the emuhion to a distance of 2 em., m e a s u r e d after initial penetration of emulsion and arbitrarily determined from 8 to 10 cm. on the scale. These readings were m a d e on each of the emulsions a t various ages in order to study the changes FIGUEE 3. PENTEAMETER i n consistency with time a n d to determine differences in consistencies asi they exist in the four emulsions made by different methods. Figure 4 shows typical curves for the emulsions. Emulsion la has a far greater consistency than any of the others. As the emulsions age, their consistencies become less until eventually the breaking point is reached and a straight line results which is identical for the four emulsions. Both the compromise emulsions rank well above the American emulsions in these measurements, and in each case emulsions fa and I I a have greater consistencies than emulsions I and 11.
Particle Size Considerable difficultywas experienced in the camera lucida studies since the great thickness of the emulsions made the preparations of slides thin enough to be subjected to this examination nearly impossible without breaking the emulsions. For that reason we were unable to obtain studies of exactly the same age for all four emulsions. However, where age differences exist, changes of globule size are taking place rather slowly; that is, the first settling has occurred and no tendency to break has begun. A cursory inspection shows that emulsion I a contains not only the greatest number of closely packed small globules, but also that the globules vary in size much less than in the other cases (Figure 5). Table VI is a summary of particle size. The smallest particles were found in emulsion l a (0.53 and 0.9 micron after 20 days and 3 mouths, respectively). This emulsion showed the smallest range in globule size, a significant fact as related to homogeneity.
VOL. 32. NO. 3
Its widespread use as an emulsifierin food emulsions is largely due to its comnlex colloidal nature. Sen. Olsen. and Kremem (6)separated iecithoprotein from egg yolk and studied each fraction of the yolk alone and in conjunction with the purified lecithoprotein in terms of effects upon the consistencies of mayonnaise emulsions. Cephalin and lecithin had destructive effects, whereas all the other fractions (cholesterol, fat, pigments, and salts) could be doubled in concentration without altering the consistency in either direction. The emulsifying agent in egg yolk was demonstrated to be an unstable complex containing both lecithin and protein, and hence called “lecithoprotein”. These results are illuminating additions to those of Corran and Lewis (0who found that lecithin, cholesterol, and mixtures of the two lower the interfacial tension between olive oil and water, despite the fact that the emulsifying agents are antagonistic, i. e., lecithin promotes the formation of oil-in-water emulsions and cholesterol promotes the formation of water-in-oil emulsions. The effect on interfacial tension is additive in the case of their mixtures, and in the proportions in which they exist in egg yolk, an emulsion of the oil-in-water type is favored. Solid powders 1*1 emulsifying agents promote that type of emulsion where the external phase is the more efficient wetting agent. L
TABLEVI. SIJXMARY OP PARTICLE SIZES(IN MIC~ONS) Metbod I la I1 II7l
-1-2 nour8- -20 no 8-3 xontbSmallest Largest Smallert Eargee% Smallest Large&
0.90 0.72
0.63
0.90
2.7 2.7 6.8
7.0
1.1
0.53 2.2
2.5
9.2 5.0 6.0 10.0
1.6 0.9
1.5 1.5
6.4
7.3 8.5 10.0
Clayton (1) predicted that anexcelleut method of preparing emulsions would be to project the interual phase in a finely divided condition inside the main bulk of the external phasei. e., out of contact with a gas phase. Ho claimed that the work of dispersion could thus he done on the internal phase, and that adsorption a t the dineric interface could be reached without the interfering adsorption a t the gas-liquid houndarv common to the u s i d agitation or stirring methods.
L._.-.COMPPOMISE-BE1IEAT6 ............. coflpunnw- ABOVE .. .‘
_ -.-.
..-._ .
Microphotographic Studies To supplement data obtained from camera lucida studies and measurements by means of an eyepiece micrometer, photomicrographs of the emulsions were taken. Wratten M plates and dark-field illumination with cardioid condenser were used on b i t e camera and microscope. A d. e. carbon arc furnished necessary light through a copper sulfatewater cooling cell; exposure time was 20-30 seconds. Figure 6 shows photomicrographs of the four emulsions which reveal findings similar to those observed with the camera lucida.
Discussion The efficiency of fresh egg yolk as an emulsifying agent has been strikingly demonstrated in them emnlsions where it constituted only 2.3-3.6 per cent of the total composition.
AGE I N HOURS F i o m 4. PENTR~WETER Cmv~s
I n those emulsions (I and If) where an air film was present a n the oil-namely, where the oil passed through 6 inches of air-we had lower specific gravities, poorer keeping qualities, larger particles of emulsified oil, a greater range of particle size, faster emulsification, and less thick (lower consistency)
0.05 mrn.
0.08 m. Method I
n
- 0.07
0.04 m. 0.0009 m. t o
-
mm.
0.06 mm.
0.03 mm.
0.05 mm.
0.04 mm. 0.03 mm. 0.05 W.
0.0064 mm.
Method Ia
0.02 mm.
W
0.04 mm.
-n
0.03 mn.
Method
k0-n
I8
0.06 m.
0.02 mm. 0.05 mm.
R
0.06 mm.
0.04 mm.
0.04 mm.
0.03 p.
mm.
0.02 m.
0.03
0.02 m.
0.04
0.03 m.
.0.01 m. W V
0.07 m.
0.02 mm.
n
0.0015 0.0085 mm.
0.06 mm.
-W
n
0.06
Method I I a
t m r
*
, 0.01
W,
0.06
I&.
IKIXI.
0.05 mm;
0.04
0.0009
m. to
0.007 mm.
0.04
0.03 m.
0.03
A
0.02 m.
0.02 mm.
0.010 mm.
0.01 m. Age:
mm.
I m n e d i a t e l y after p r e p a r a t i o n
W" Age:
3 months
FIGVRE 5. CAMERA LUCIDADRAWINGS Particle size variation is given for each method in millimeters, 419
0.01 mm.
INDUSTRIAL AND ENGINEERING CHEMISTRY
420 Method I
Method I s
VOL. 32. NO. 3
of dismrsed nliase and such low concentra-
American-above) iii producing emulsions of high stability and homogeneity. 3. The int,roduction of the disperse phase beneath the siirface of oil-in-water emulsions measurably improves the stability, consistency, and homogeneity of such einiilsions. 4. Ampere-r. p. m. data may be significant iii the study of the emulsification proccss and as consistency measurenients. 5. The pentraineter is a siiitahle instrument for tlie measurement of the consistencies of thick eniiiisions and gels of the type studied. It is morc useful for such mixtures than the inobilometer. Method t1 PIQURE
Method Ita
OF FOURTYPES OF E ~ n r . ~ i o vTAKEX s TMMEDIATELY AFTER I'HEPARATION ( X 970)
6 . PemoMmnoonnptrs
eniulsions than those where the oil w&s protected ironi the air by injecting it into the emulsions heneath the surface. These facts would seem to bear out Clayton's prediction, especially since approximately 3 per cent of emulsifying agent eficiently holds 89-93 per cent of oil in a stable emulsion. In each case also the compromise emulsions were superior to those of the American type in stability and homogeneity. The preliminary treatment of the emulsifying agent with a small quantity of the internal phase brought about a finer dispersion of the yolk emulsifrers tlian existed in the prebeaten yolk. Figure 7 illustrates rather p00~1ythe condition at optimum dispersion. Achieving this optimum dispersion previous to the introduction of the hydrogen ion of the acid vastly increases the efficiency of the yolk emu1sifieTS in that the emulsifying film is proliably Iwth stronger' and thinner than it would be otherwise. Woodinan (7) suggests that the efficiency of intermittent, emulsification is due to increltsed facilities for adsorntioii offered by rest intervals, arid CLdytoll predicted that when the dispersed phase is injected into the coiitiriuoun phase below tho surface, intermittent inject,ion would confer no acivantage, Preliminary oxpeiiments showed steady beating to produce lnore stable emulsions than those prepared hy intermittent heatinx, and lierice steady heating was used t~liroogliout. It is posnihle that further experi1ncnt.s making i i s c of intcrniittent injections benentlr the stirface will be
