February 1950
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INDUSTRIAL AND ENGINEERING CHEMISTRY
where the low capacity of the resin for ascorbic acid is limiting. Means of circumventing these two difficulties would materially increase the economic feasibility of the process. There is a good possibility that characteristics of the anion exchange resin could be modified to give a much greater capacity for ascorbic acid. A preliminary economic study of the process as it might be applied to a typical walnut-growing district, was made at this laboratory. Based on the availability of 5000 tons of hulls (containing 25 tons of ascorbic acid) in a localized area over a 30-day period, and a 25% yield, it was estimated t h a t recovery of $100,000 worth of ascorbic acid per year would require a capital investment of $300,000 which is too high to make the process attractive commercially. Of this $300,000, $175,000 is required for equipment to recover and concentrate the walnut-hull extract. This rather high cost of extraction and concentration equipment is a consequence of the large volumes of dilute solutions that would be handled during only 1 month of the year, and the corrosive nature of the solutions*which necessitates stainless steel or other resistant material. Lengthening of the processing season by a n inexpensive method of storing green hulls and increasing the over-all yields would materially decrease the ratio of capital investment to annual value of product. ACKNOWLEDGMENT
V. F. Kaufman of this laboratory made the economic study and supplied the cost data. Hans Lineweaver determined the ascorbic acid oxidase in walnut hulls. Others in the Western Regional Research Laboratory t o whom the authors are indebted in-
39 1
clude: H. D. Lightbody, W. B. Van Arsdel, W. D. Ramage, J. H. Thompson, A. H. Brown, and P. W. Kilpatrick. The late Clyde Barnum provided technical information and assistance in the procurement of raw materials, and A. W. Christie, Grant Burton, C. C. Anderson, Edward Bunker, and others in the California Walnut Growers Association gave helpful assistance. LITERATURE ClTED (1) Bukin, V. N., and Garkina, I. N.,B i o k h i m i y a , 7, 59 (1942). (2) Gherghelenhiu, A. K., B u l l . A p p l i e d B o t a n y Genetics P l a n t Breeding ( L e n i n g r a d ) , Suppl. 84, 206 (1937). (3) Hennig, K., and Ohske, P., Biochem. Z., 306, 16 (1940). (4) Klose, A. A., Peat, Jean, and Fevold, H. L., P l a n t Physiol., 23, 133 (1948).
(5) Loeffler, H. J., and Ponting, J. D., IND. ENG.CHEX.,ANAL.ED., 14,846 (1942). (6) Matchett, J. R., Legault, R. R., Nimmo, C. C., and Notter, G. K., IND. ENG.CHEY.,36, 851 (1944). 152, 447 (7) Melville, R., Wokes, F., and Organ, J . G., -\'ahre, (1943). ( 8 ) Mottern, H. H., and Buck, B. E., U. S. Patent 2,433,583 (June 15, 1948). (9) Pyke, M., Melville, R., and Sarson, H., N a t u r e , 150, 267 (1942). (10) Wokes, F., Organ, J. G., Duncan, J., and Jacoby, F. C., Biochern. J., 3 7 , 6 9 5 (1943). RECEIVED June 13, 1949.
Isothermal and Isobaric Degassing of Ice Cream ALFRED LACHMANN, E. L. JACK, AND D. H. VOLMAN University of California, Davis, Calif. T h e effect of degassing ice cream of definite composition has been studied. The air liberated from the ice cream structure was measured quantitatively under controlled temperature and pressure conditions. I t has been observed that the amount of air liberated from the ice cream is related to both the temperature and the pressure to which the ice cream is subjected. This relationship can be used for a determination of the strength and permeability of a particular ice cream structure.
T
HE degassing of ice creams isothermally and isobarically has
been investigated with particular reference to the amount of air liberated and its relation to the strength and permeability of the ice cream structure. When air escapes from ice cream a decrease of ice cream volume is observed at certain pressures and temperatures. The amount of air liberated depends partly on the structural strength and permeability of an ice cream of fixed composition. The strength of the structure may be weakened by a multitude of factors. I n addition t o the composition of ice cream, the manufacturing procedures are of great importance and can influence the stability of the ice cream mix. Homogenization pressure, different freezing techniques, percentage of incorporated air (overrun-Le., the increase in volume of the ice cream over the volume of mix expressed as per cent of the volume of mix), temperature changes in hardening room and storage cabinet are only some of the factors which play a great part in the structure of the final ice cream product. On the basis of results of a large number of investigations, various theories have been proposed interpreting the weakening of the ice cream structure (1-13).
From all the studies it is to be expected that fracture of air cells enclosed in the ice cream structure would be accompanied by diffusion of the incorporated air from the ice cream. The diffusion rate is related t o the rigidity and permeability of the particular ice cream structure. Therefore, the change of' external temperature and pressure and its effect on ice cream in relation to the amount of air liberated can give information about the strength and imperviousness of ice cream if the volume of air liberated a t selected temperatures and pressures is measured quantitatively. No publication of this type of investigation has been reported. APPARATUS
Figure 1 shows the apparatus used in the investigations. It is composed of the reaction chamber containing a weighed amount of ice cream of a definite composition. This vessel has the shape of a large test tube with a capacity of approximately 350 t o 375 ml. Its opening is wide enough to allow an easy drawing of the ice cream into the container from the freezer unit. A Dewar flask filled with an alcohol-dry ice mixture provides the cooling at the desired experimental temperature. The gas buret of 50-ml. volume graduated in 0.1 ml. is used to measure the volume of air liberated. It is immersed in a water jacket to keep the temperature constant during the investigation. The bottom of the buret is connected with a mercury reservoir permitting pressure regulation by manipulation of the stopcock. With this arrangement no leveling bulb is necessary, With a water aspirator, the desired pressure is obtained and measured by the attached mercury manometer. PROCEDURE
PREPARATION OF ICECREAM. Fresh cream of 30 t o 35% fat,
milk, skim milk, and condensed skim milk of approximately 35y0 total solids were the milk products used for the experimental mixes. The composition of the ice cream mix was as follows:
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Fat, % Milk solids, not fat, Sugar, % Stabilizer (sodium alginate), %
12.0 10 5 15 0 0.22
---
Total solids, %
37.72
The mixes were pasteurized at 71.1 O C. (160" F.) for 30 minutea and homogenized by means of a viscolizer a t a pressure of 2200 pounds per square inch. The flavoring material consisted of pure vanilla extract. The mixes were promptly cooled below 10.0" C. ( 5 0 " F.) and stored at an approximate temperature of 4.4" C. (40" F.). PRELIWIKARY TESTS.The total volume of the reaction chamber, the specific gravity of the ice cream mix, and the amount of dissolved air in the mix were determined. The amount of dissolved air averaged 2.0 to 3.0 ml. a t 760 mm. of mercury and 0" C. Calculation showed this amount to have no significance in affecting the results.
T 1 1
I I
I
I
I I
Y
I I
e
EXPERIVENTS A T CONSTAST PKESbURE. The procedure was basically the same. Instead of varying the pressure, the temperature was gradually raised from -45" to -16" C. and the amount of liberated air measured until equilibrium was reached.
CALCULATIONS
The measured amount of air was converted to normal ronditions on the basis of the gas laws. UQ =
2,
(273.2) p o (273.2
+ Ti
u = volume of measured air p = experimental pressure t = temperature of the gas buret
DETERMINATION OF ICEC m - m VOLUME. Inasmuch as it was impractical to fill the reaction vessel completely with ice cream, it was necessary to determine the volume of ice cream and correct the results for the air in the free air space. Ice cream in the reaction vessel 11as weighed and this weight wab considered to be the weight of mix since the weight of the incorporated air was insignificant. The volume of the unfrozen mix was calculated from its weight and specific gravity. By rearranging the formula for calculation of overrun based on its definition-
yo overrun
= volume of ice cream - volume -
The volume of the frozen ice cream is given by:
I
Volume of frozen ice cream = yooverrun X volume of mix I00
I I
I
of mix
volume of mix
PI I
ST
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x 1m
+ volume of mix
I
I
1 I I
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RESULTS
ISOTHERMS. Figure 2 represents the data of three experiments conducted a t the same temperature. The difference consisted in
I
1
L
mercw-
Figure 1.
Apparatus for Isothermal and Isobaric Degassing of Ice Cream
F PREPARATION OF SAMPLES.The mix was frozen in an experimental Taylor batch freezer to about -4 C. and whipped to an overrun of approximately 100yo. Overrun determinations were made by weighing a standard volume of the ice cream before and after freezing. The reaction chamber was filled with the partly frozen ice cream and placed in a Dewar flask containing a n alcohol-dry ice mixture to complete the freezing to the temperature desired for the experiment. After holding 2 to 3 hours to ensure temperature equilibrium, it was connected to the measuring device by means of a ground glass joint. As one experiment lasted from 2 to 4 weeks, the reaction chamber and Dewar flask were stored each night in a refrigerated cabinet. It was posiible with this arrangement to maintain the temperature within * l o C. DEGASSING. Two series of experiments were conducted. In one series the experimental pressure was lowered isothermally a t selected temperatures ranging from -10" to -50" C. and in another series the temperature was raised isobarically a t selected pressures from 760 to 300 mm. of mercury. EXPERIMENTS AT CONST4NT TEMPERATURE. The reaction chamber was connected to the measuring device, the gas buret filled to the zero mark with mercury, and the initial experimental pressure adjusted to 760 mm. of mercury. When the reaction chamber was opened, the air diffusing from the ice cream structure created a slight positive pressure in the closed system which was equalized by the mercury column in the gas buret. Readings were taken periodically depending upon the rate of diffusion until an equilibrium was approached. -4s the diffusion never stopped completely, equilibrium was considered to be attained when 0.2 to 0.3 ml. of air was liberated after 3 to 4 hours of continuous degassing. The pressure in the system was gradually decreased stepwise until the final pressure of 19 mm. of mercury was reached. The time required for one complete expeiiment varied from 15 to 25 days. O
I
0
I
/00
I
I
200
300
400
rnm.
Hy
500
600
700 760
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February 1950
30
-
40
-
50
-
60
-
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p = 500 mm. My
-
p 300 flm. H3
2: 70-
I
100
I
200
I
$00
I
400
500
600
I
air liberated was collected at lower pressures. At -40" C., the ice cream structure was so firm that no significant amount of air was collected throughout the experiment. The same is C. However, the large true a t the temperature of -50' amount of air liberated a t -45" C. and 19 mm. of pressure cannot be explained. ISOBARS.The isobaric curves showed, in general, the same trend as the isothermic curves. Table I1 and Figure 4 represent the data. A maximum inflection was found at a single temperature and pressure in good agreement with the similar point derivable from the isothermic curves.
,
700 760
mm. J@
.
the pressures to which the ice creams were subjected. In the first experiment, the pressure was reduced from 760 to 500 mm. and then further reduced by a 100-mm. interval. The largest quantity of air liberated from the ice cream was collected a t 500 mm. of pressure. From 400 to 19 mm. the amount of air diffused was almost constant. DISCUSSION AND CONCLUSION I n the second experiment decreasing the pressure to 700 mm. resulted in liberation of a slight amount of air. At 600 mm. the The authors' interpretation of the characteristic form of the delargest amount of air liberated was collected for this particular gassing curves seems t o clarify, at least partIy, the mechanism involved when ice cream was degassed a t different temperatures experiment. Further pressure decreases in 100-mm. intervals and pressures. The air in the ice cream structure is in a disconagain yielded a n almost constant volume of rtir recovered for each tinuous phase, and the air cells have the form of irregular bubbles determination. The graph illustrates the maximum inflection at surrounded by semisolid films. The thickness of these lamellae 600 mm. and the leveling o f f to a straight line for the ensuing influences the strength and permeability of the structure. As long as the pressure differential is not great enough t o fracture the air pressure changes. I n the third experiment, the pressure was decreased gradually in 50-mm. intervals. At 550 mm. the quantity of air OF ICECREAM AT SOME SELECTED TEMPERATURES TABLE I. ISOTHERMAL DEGASSING liberated was the largest. The shape of Expt. No. 3A 4B 2B 5A 2A 6 8 9 11 this curve was characteristic of most Overrun, % 103 95 108 95 103 102 102 102 95 curves determined. The amount of air .-. Amount of Air Liberateda, MI., a t Pressure on evolved was insignificant until it reached Ice Cream, -10.4 -16.4 -20.4 -20,60 c. -25.4 -35.5 -40.4 -50.8 c. 0 c. 0 c. c. a maximum and leveled off in a linear Mm. H g 0 c. c. c. 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.0 relationship. 0.0 ... 0.8 0.5 0.0 0.6 13.4 0.0 1.0 1.7 ... 1.0 0.8 0.12 1.3 Table I and Figure 3 illustrated the ... 3.6 .. 5.1 . . . 1.5 0.5 0.49 1.0 17.6 25.3 results of isothermal degassing for vari20.3 ... 10.2 0.6 0.12 0.9 ... .. 6.9 7.0 37.9 16.4 0.3 0.86 1.2 5.9 16.5 ous seleited temperatures. At -10' C. 6.7 ... 9.7 0.6 0.19 4.3 ... 7.2 the ice cream structure was so soft that 6.0 14.5 9.8 0.6 0.37 1.1 14.1 6.8 9.0 0.7 0.55 1.6 .. ... .. the pressure could not be reduced to less .. 14.1 8.1 1.7 0.0 1.1 .. 14.2 .. .. 1.4 0.74 1.2 ... .. than 700 mm. A considerable amount of 2.0 0.0 0.9 .. 13:8 ... .. 14.0 , . . 70.0 0.43 1.0 air, however, was released at this partic.. .. ... 7.8 0.19 1.4 100 .. 14.6 .. 14.5 ... ular pressure. At -16" C. the larg... 8.2 0.12 1.0 50 , , 44:3 7.3 8.7 i : o _ -4 .7 - 5-1 . 25.0 0.43 0.4 .. L O 5.4_ 5_ 19 est quantity of air was evolved a t Total amt. of 600 mm. When the temperature was 98.5 106.8 117.7 100.7 4.61 19.0 air liberated 13.5 97.3 113.8 gradually decreased to -35' C. the ice a This amount is calculated for 200 00. of ice cream and converted to normal conditions of 760 mm. and cream structure became more rigid. 00 c. Consequently, the largest quantity of I
0
0
0
*.
. I .
- -
~
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INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE 11.
DEGASSING O F ICECREAM SELECTED PRESSCRES
ISOBARIC
AT S O X E
Ab-. T e m p . of Cooling A m t of -4ir B a t h , C. Liberateda. Mi. EXPT.No. 12, 1007, OYERRUN 40 0 0 760 40 0.0 700 -35.6 0.23 700 -30.4 700 0.0 -26.7 0.62 700 -20.3 0.58 700 -15.6 2.42 700 __ Total 3.86 EXPT.N o . 13, 1037' OVERRUT -40.7 0.0 760-650 -40.4 0.0 600 -35.2 0.0 600 -30.1 0.8 600 -25.3 1.4 600 -20.4 5.0 600 15 4 -16.5 600 Total 22.6 EXPT.S o . 14, 97% OX-ERRIX -41.5 3.3 760-550 1.1 -40.7 500 0.1 -35 8 500 0.7 -30.4 500 -25.7 36.0 500 -20.0 2.8 500 -18.0 1.0 500 Total 48.0 EXPT.No. 15, 100% O V E R R U N -40.2 0.4 760-450 -39.8 0.0 400 -35.6 10.1 400 -30.7 36.2 400 -26.0 4 9 400 -20 8 3.4 400 -1s.i 1.0 400 Total 56.0 EXPT.No. 16, 987, OVERRUN -40.0 4.5 760-350 0 6 -40.0 300 49.8 -35.4 300 3.5 3 0 . 7 300 3.7 -25.3 300 1.6 2 0 . 4 300 1.0 -16.0 300 Total 64.6 a This amount is calculated for 200 cc. of ice cream and converted to normal conditions of 760 mm. and 0' C.
Pressure on Ice Cream, Mm. H g
-
cells a t any g i v e n temperature, the amount of air liberated from the structure r i l l be relatively small. When the pressure is decreased or the temperature increased t o a point where the air cells are fractured, the amount of air liberated will be c o n si der ably larger than if the cells are intact. The air diffuses from the rigid s t r u c t u r e and during its passage forms cont i n u o u s channels, thereby changing the ice cream structure. When equilibrium between the air in the ice cream and the applied pressure is attained and then the applied pressure is further decreased, the residual air can easily escape through the porous ice cream structure. Furthermore, the volume of the residual air is in accordance with the gas laws, inversely proportional to the pressure and should plot linearly. The curves (Figures 3 and 4)
Vol. 42, No. 2
constructed from the experimental data support this interpretation. I n addition to the volume relationships, the rate of diffusion also changes a t the temperature and pressure differential point where cell fracture occurs. The air behaves as in a free space upon further changes in temperature or pressure. It has also been observed that the maximum quantity of air liberated is related to both the temperature and the pressure, to which an ice cream of a definite composition is subjected (Figure 5). If t.he pressure a t which the largest amount of air is liberated is plotted as ordinate and the respective cooling temperature of the ice cream as abscissa, two curves for the isothermal and isobaric degassing result. Both represent the strength of a particular ice cream and indicate to what pressure and temperature it can be subjected without undue weakening of the rigid matrix. I n these experiments, ice cream held at -40 a C. has such a rigid structure that only an insignificant amount of air will be liberated a t even a very IOTT pressure. At -20" C. the structure is weakened to such an extent that a reduction in applied pressure t o 600 to 550 mni. will be sufficient to fracture the air cells. It is believed that application of these results can be made to a study of the shrinkage problem in ice cream. Assuming that the tendency to shrink is related to the structural strength of the air cell lamellae, then the quantitative determination of the lamellae strength should serve as a guide t o possible shrinkage. Referring to Figure 5 it will be observed that the break in structure, for this particular ice cream, occurred a t a definite pressure and temperature. If, in anot'her ice cream, the breaking point should come a t a higher pressure for the particular temperature or a t a lower temperature for the particular pressure, this condition would indicate weaker lamellae and probably a greater tendency tovard shrinkage. Experiments are being conducted to observe the struct'ural strength in ice creams prepared with different treatments. SU413IARY
Ice creams of fixed composition have been degassed in one series of experiment,s by lowering the applied pressure isothermically a t selected temperatures between - 10 O and -50 O C. and in another series by raising the temperature isobarically a t selected pressures between 1760 and 300 mm. The amount of air escaping from the ice cream has been measured. Curves representing the isothermal and isobaric experiments have been constructed. T h e n the degassing is conducted a t constant temperature, a maximum quantity of air is liberat,ed a t a definite pressure, and, conversely, when the degassing is conducted a t constant pressure, a maximum quantity of air is liberated at a definite temperature. The data are discussed in terms of strength and permeability of the ice cream structure. ACKNOWLEDGMENT
This work was supported in part by funds supplied by the California Dairy Industry Advisory Board. The authors also wish to acknowledge H. Shipstead for suggest,ions in certain phases of the work. LITERATURE ClTED
Bendixen, H. A., Ice C r e a m Rev., 31, No. 7 , 149 (1948). Cole, W. C., Ice Cream Field, 34,No. 4 , 32 (1939). (3) Cole, 77'. C. and Chase, E. S., R e p t . Proc. I n t e r n . Assoc. Ice
(1) (2)
C r e a m M f r s . , 42nd Ann. Conv., 2, 75 (1946). (4)
Dahle, C. D., Hankinson, D. J., and Meiser, J. A., Jr., Ibid.,
p.
64.
( 5 ) Erb, J. H., C a n . D a i r y Ice Cream J.,20, KO. 3, 66 (1941). (6) Erb, J . H., Ice C r e a m Trade J . , 36, No. 3, 58 (March 1940). ( 7 ) Hankinson, D. J., and Dahle, C. D., Southern Dairy Products J . . 36, No. 4 , 17 (1944); Ibid., No. 5, 34 (1944). (8) Kohler, R., R e p t . Proc. I n t e r n . Assoc. Ice Cream Mjrs., 59th Ann. Conv., 2, 28 (1939). (9) Ramsey, R. J., I b i d . , 2, 58 (1946). (10) Sommer, H . H., "The Theory and Practice of Ice Cream Making," 5th ed., Madison, \Vis., published by author, 1946. (11) Tracy, P. H., Hoskisson, TV. A,, and Weinreich, P. F., R e p t . Proc. I n t e r n . Assoc. I c e Cream Mfrs., 4 l s t Ann. Conv., 2, 16 (1941). (12) Tracy, P. H., and Ruehe, H. A , , "Enzyme Activity of Ice Cream Improves," Vn'niv.I l l i n o i s , A g r . Expt. S t a . Bull. 333 (1929). (13) Turnbow, J. D., Tracy, P. H., and Raffetto, L. d.,"The Ice Cream Industry," 2nd ed., New York, John Wiley & Sons, Inc., 1947. RECEIVEDApril 16, 1949. Presented before t h e Division of Agricultural a n d Food Chemistry a t the 115th Meeting of the AMERICANCHENICAL SOCIETY,San Francisco, Calif.
