I.VDliSTRIAL AND ENGINEERING CHEMISTRY
966
ment at this one point as sufficient to permit the approximations desired, we have let Y equal the mol fraction of carbon monoxide converted to methanol and P equal the total pressure, then for the reaction CO 2H2-+CH30H - [ P C O ' ] x [PH%'I2 1- Y 4P2( 1 - Y)'
+
K P
-
and log K,' = log
(1 - Y)3 Y ( 3- 2 Y)'
log Y ( 3 - 2 Y p
which reduces to (1--13
log Y(3-2Y)'
+ 2 log P + log 4.0
Q
4.571T
+ 3.5 log T + 2.9979-2
log P
Acknowledgment
-- Q
4.571T ZV?,75 log T
+
=
(3-2Y)2
Substituting for log Kpl in the approximation formula (l), we have (1- Y)3 =
20, KO. 9
The values obtained for Y in our calculations are graphically represented in Figure 10. Although possibly approximate, this curve gives a good estimate of possible yields under a I PY 4P2(1-Y)3 reactant pressure of 180 atmospheres. Our experimental 3 - 2 Y c Y(3-2Y)2 conversions a t 400" C. have been indicated in Figure 10.
='3-2YX
[PMMeOH]
VO!.
+ rvc-2
log P -log 4 (2)
The writers are indebted to W. P. Yant, in charge of the gas laboratory, and his staff for many gas analyses, and to A. C. Fieldner, chief chemist of the Bureau of Mines, for his interest and patient support of this investigation.
Textures of Ice Creams as Influenced by Some Constituents' Meta H. Given HOMEECOXOMICS DEPARTMENT, EVAPORATED MILKASSOCIATION, CHICAGO, II.L.
NE of the most agree-
0
able qualities in ice cream is fine, velvety texture, free from lumps of fat and ice. Those familiar with the production of ice cream know that texture is dependent upon the constituents of the mix, the proportion and condition of those constituents, and the technic used in freezing. This paper has to do x i t h the effect of some constituents on texture. Influence of Constituents on Water Crystal Formation
Water in the ice-cream mix freezes into crystals. The fineness or coarseness of the texture of ice cream depends upon the size of the ice crystals. The size of the crystal depends upon the even distribution of numerous tiny air bubbles in the ice cream, which in turn depend upon the viscosity of the mix. Mixes containing gelatin, eggs, and dry egg yolk show greater viscosities than the check. Although the variations in the viscosity readings are not great, the differences are much more apparent in handling the mixtures. Homogenization and aging increase viscosity. A single homogenized constituent like evaporated milk increases the viscosity and improves texture equal to that oE 0.3 per cent gelatin, 2.5 per cent raw egg, or 0.3 per cent egg yolk.
Ice cream contains from 60 to 70 per cent water and from 30 to 40 per cent solids. Since the milk fat exists in microscopic globules in emulsion, the sugar in true solution, and the milk proteins principally in colloidal solution, ice cream is a complex mixture from both physical and chemical standpoints. I n the freezing process the water of the mix congeals into tiny crystals. The finest possible crystals are desired, so fine that they can be scarcely felt on the tongue. The tongue test is a reliable, practical, and delicate one for judging texture. The microscope, however, reveals crystals that cannot be felt on the tongue, and is therefore our most useful aid in making fine distinctions between ice creams. It is well known that if water alone is frozen in an icecream freezer and beaten, an icy mush consisting of large crystals results; if the mass is not beaten, a solid lump of ice forms. In ice-cream mixtures the solids in true and colloidal solution interfere with the formation of large water crystals. The size of the solid particles in emulsion also has an influence on the texture.2 Microscopic examinations of fine-textured ice cream always show numerous tiny water crystals with small, well-distributed 1 Received April 7, 1928. Paper presented before the Biological Division of the Chicago Section of the American Chemical Society, February 24, 1928 2 Brainerd, Virginia Agr. Expt. Sta., Tech. Bull. 7 .
air cells. Grainy textured creams show large and irregular shaped crystals with large air cells less evenly distributed. The incorporation of a large amount of air in such a way that it is evenly distributed in tiny bubbles throughout the ice cream, therefore, is a condition of fine texture. When viscous mixtures are beaten they are stretched out into thin, cohering films, which readily envelop air in very small sacks throughout the mass. This is why egg white permits so much air to be beaten into it. Air may be beaten into ice-cream mixtures also, provided the viscosity of the mixture is sufficient to retain the necessary amount of air. The value of these small and numerous air cells depends on the fact that the air acts as so much intervening solid substance between the water crystals, preventing the merging of many small crystals into a few large ones. It is a well-known physical principle that a tiny air bubble will withstand more pressure from the outside than a large one. This explains why fine-textured, firm-bodied ice creams remain smooth on standing, while light, fluffy ice creams containing large air bubbles settle and acquire a very coarse texture. The quality of the ice cream, then, is greatly affected by the quantity of the air incorporated, as well as by the size of the air cells. Experimental work of Ruehe3 and of Mortensen4 demonstrates this fact. Manufacturers' Practices
Manufacturers have learned that viscosity may be greatly increased by the introduction of solids other than milk solids into the mixture. Some of the substances used are gelatin,5 cornstarch, gum tragacanth, dried egg yolk, and whole egg.6 a 4 5
6
Ice Cream Trade J . , 20, 57 (1924). I b i d . , 20, 74 (1924). Sommer, Ibad., 23, 47 (1927). I b i d , 23, 64 (1927).
967
INDUSTRIAL AND ENGINEERING CHEMISTRY
September, 1928
Pormuia 1
Formuls
Formula 2
Formula 6 Photomicrographs of Ice Cream Prepared by Formulas Given i n Table I.
Formuin 6
Formula 4
198
x
her of fat globules have a much greater surface8 on which the other milk solids, especially the proteins, are adsorbed. The result is a more stable (?muisionand a more viscous mixture with increased surface tension.'O Experimental
The purpose of this experimental nrork was to det,ermine tlre effectiveness of
fiornogenired (evapoioted) milk
Photomicrographs of Fat Globules in Mllk.
Raw milk 900
With a desire to obtain maximum viscosity many producers are using texture improvers to e x e m and are obtaining objectionable products that are gluey in consistency. Two other mays of incrcasine viscositv that hsve been recently employed are aging? an; homogeiiination. Ilomogeniaation is a process that not only breaks up the clumps of fat globules but actually breaks up the large individual globules as much as one thousand times8 The increased num7
8
Leighton and Wiiliams, 1.Phyr. Cham., 81, 1663 (19271. Welgner, Kolloid-Z., 15, 105 (19141.
evaporated milk in producing a desirable texture in ice cream, comparing the texture thus produced with that produced by the addition of gelatin, whole egg, and dry egg yolk. Photomicrographs were made of each ice cream for the dernon&ration of text,ure. The formulas used mere based upon an ice-cream formula commonly used in the trade. This formula (l), together with others employed in the experimental work, is given in Table I.
x
Table I-Content FKM"L*
1 (check1 3 5 ~
6
*
sua*=
cn**lr
14 14 14 14 14 14
32 32 32 31 32 28
of Ice-Cream Mires IYI*RYBT MILX
(25% fat1 (4% fit1 Pm cent Per Cent Per cent
54.0 53.7 53.5 62.6 63.7 36.0
OTHBR INOIi*D,SNrn
P" 0 Geirtin Gelatin Wholerawegg Dryeggyolk rivaporaled milk
Mortenren, Iilr Cream R a d e J . , 20, 74 (1924). m Reid and Moreiey, l a i d . , 28, 57 (19271.
CE"f
0.3
0.5 2.5 0.3 22
968
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 20, No. 9
The time required for freezing having been previously graphed using an ordinary photographer’s camera and a determined, the four samples of each mixture were made up Bausch and Lomb microscope. a t intervals of 90 minutes in order that the aging of each Results and Discussion should be of equal duration. In preparing the first mixture, the milk was heated to the The accompanying photomicrographs illustrate the inscalding point. Then it was poured into a sterile bottle and fluence of the various additions on the texture of ice cream. the sugar added. After cooling, the cream was introduced; Formula 1 is seen to produce large, irregular crystals. Finer then the mixture was placed in an ice box and allowed to crystal construction was obtained by formula 2, which constand until the following day. In preparing second and third tains 0.3 per cent gelatin. Formula 3, 0.5 per cent gelatin, mixtures the gelatin was softened in a little cold milk and dis- gave the finest texture of all ice creams made-so fine that it solved in the rest of the milk heated to the scalding point. was almost gummy and for this reason objectionable. The Sugar and cream were added as in the check. In the fourth flavor was also poor. The micrograph for formula 4 points a custard was made of the thoroughly beaten raw egg and out the effectiveness of raw egg which has been cooked with scalded milk. Sugar and cream were added as in the check. milk as a custard. A similar improvement is shown in the The dry egg was combined in the same way as the gelatin. case of dry egg yolk, formula 5. Formula 6 is the ice cream In the sixth the bottled milk was heated to the scalding point containing evaporated milk and no solids other than those and cooled; then the evaporated milk and cream were in the first ice cream but there is a much finer texture. In added. fact, the improvement is quite similar to ice cream containing All mixtures were frozen the following day. Just before 0.3 per cent gelatin. freezing, the temperature was taken, and the viscosity deViscosities of all the mixtures showed little variation when termined with a Mojonniet’s viscometer. I n every case the observations were made on the viscometer. The differtemperature was 12” C. The viscosities were: (1) 16; (2) ences, however, were very apparent when the mixtures were 17; ( 3 ) 18; (4) 17; (5) 17; (6) 17. The freezer used was poured from one vessel to another-formulas 2, 4, 5, and 6 an attachment of a Hobart mixer. The ice used for freezing appearing to be about the same in viscosity but much more was finely chopped and mixed with ice-cream salt in the pro- viscous than formula 1, which contained milk and cream. portion of 6:l by weight. The freezer was turned a t medium Formula 3 was the most viscous of all. The increased visspeed. Each sample was frozen 20 minutes, which produced cosity of the evaporated milk mixture is due entirely to the in all cases ice cream that was quite solid. evaporated milk itself. Its own viscosity is a result of the Cream from each freezer was removed to a pint card- finely divided state of the fat globules in the milk that has board carton and then placed in a special container packed been brought about in the homogenizing process,6 and the with ice. The frozen creams were transferred to cold storage action of heat in sterilization on the casein. Photomicrowhere they stood for 3 days a t a temperature of -14” F. graphs showing the effect of homogenization on fat globules (-26” C.). The photomicrographs were made in this cold- are also shown. storage room to keep the ice cream solid or in crystalline form. Acknowledgment Gauze-thin slices were cut from the center of each ice-cream The author is indebted to the Home Economics Departpackage with a safety razor blade. Specimens were placed on an ordinary microscopic glass slide with a cover glass on ment of the University of Chicago for the use of a research top. They were then examined to see if they were alike in laboratory, and to Armour and Company for the privilege texture. A representative slide from each group was photo- of using a cold-storage room.
Vitamin B Content of Avocados’ LeRoy S. Weatherby and Eugene W. Waterman CHEMICM. LABORATORY, UXIVERSITY OF SOUTFIERN CALIPORXIA, Los ANGELES, CALIF.
The vitamin B content of avocados was determined of its long season. It averages ORK by Santos2 showed vitamin B through feeding experiments with albino rats. The about 25 per cent of oil conpulp of fresh food was used and was compared with tent. Thefruitusedwassuch to be present in Fleischmann’s dry yeast as standard. It was found that as through exterior blemish avocados in relatively high quantity. His work was the fresh pulp contained approximately one-twelfth failed to meet the requirethe vitamin value of the dry yeast. ments of first-grade fruit, done on the residue of dried but which met the standard fruit after the oil had been extracted nith ether. I n this investigation it was thought requirements in every other n-ay. advisable to determine the vitamin content of the fresh ripe The vitamin B content was determined in the customary way through feeding experiments with albino rats, using yeast fruit of standard variety as actually consumed. The fruit tested goes under the trade name of “Calavo.” as a standard of comparison. which is the copyrighuted name of the highest grade of avocados Preliminary Experiment put out by the Calavo growers of California, in which the fruit is required to meet certain high specification standards In the first preliminary experiment, rats from three litters, of quality and of maturity. The Fuerte variety was used of ages varying from 28 to 33 days, were distributed among becquse it is one of the most popular varieties and because three cages. The basal diet common to all the animals was * Received March 16. 1928. Presented before the Intersectional Meet- a modification of the Osborne and Mendel vitamin-B-free diet, ing of the Amencan Chemical Society with the Pac:fic Division of the in which meat residue was substituted for the extracted casein. American Association for the Advancement of Science, Pomona, Calif., The meat residue was prepared by extracting finely ground, June 13 to 16, 1928. lean round steak with hot water three times and then drying 2 A m . J . Physiol., 69, 310 (1922).
