I N D U S T R I A L A N D ENGINEERING CHEMISTRY
August 1948
ACKNOWLEDGMENT
The authors are indebted to C. 0. Willits and his co-workers for determinatipn of saponification equivalents and 'to T. J. Dietz and associates for Williams plastometer measurements. LITERATURE CITED
(1) Aten, A. H. W., J. Chem. Phys., 5, 260 (1937). (2) Barrett, H. J., and Strain, D. E., U. S. Patent 2,129,662 (1938). (3) Bilterys, R., and Gisseleire, J., BUZZ. soc..chim. Belg., 33, 122 (1924). (4) Boggia-Lera, E., Gazz. chim. i t d , 29, 441 (1899). (5) du Pont de Nemours & Co., E. I., IND.ENG.CHEM.,28, 1160 (1936). (6) Hill, R., U. S. Patent 2,129,690 (1938).
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(7) Kautter, C. T., Brit. Patent 620,164 (1940). (8) Klages, F., Be?., 76, 788 (1943). (9) Lievens, G., Bull. soc. chim. Belg., 33, 122 (1924). (10) Neher, H. T., IND. ENO.CHEM.,28, 267 (1936). (11) Rehberg, C . E., Faucette, W. A., and Fisher, C. H., J. Am. Chem. SOC., 66, 1723 (1944). (12) Rehberg, C. E., and Fisher, C. H., Ibid., p. 1203. (13) Ruhoff, J. R., and Reid, E. E., Ibid., 55,3825 (1933). ENG. (14) Strain, D. E., Kennelly, R. G., and Dittmar, H. R., IND. CHEM.,31,382 (1939).
(16) Van Antwerpen, F. J., Ibid., 35, 126 (1943). (16) White, T., J.Chem. SOC.,1943, p. 238. (17) Williams, Ira, Ibid., 16, 362 (1924). RECEIVED April 13, 1947. Presented before the Division of Paint, Varnish, and Plastics Chemistry at the 109th Meeting of the AMERICAN CHEMICAI, SOCIETY, Atlantic City, N. J.
Oxygen Absorption by Dehydrated Whole Egg Powders BENJAMIN MAKOWER AND THOMAS M. SHAW Western Regional Research. Laboratory, Albany, Calif.
The initial rate of oxygen absorption by several dehydrated egg powders was measured as a function of temperature, pressure of oxygen, specific surface, and moisture content. For one powder the variation of rate from 1 to 1270 water, in the dark, at 25.1' C. can be given by the empirical expression (Equation 1): Initial rate at 1 atmosphere of oxygen in cc. of oxygen per kg. of solids per hour equals 0.36 (% water)/[l 0.64 (70 water)]. The energy of activation of the reaction, from measurements a t 15.1°, 24.8", and 35.0' C. at 1.8470 water is 22 kg.-cal. Five different egg powders (two lyophilized and three spray-dried) at 2.4q0 water, of different specific surfaces varying from 0.12 to 0.83 sq. meter per gram showed nearly the same rate of absorption of oxygen. The rate is approximately proportional to the square root of oxygen pressure and is markedly accelerated by light. This data in conjunction with other observations may be used to estimate the extent of flavor change with time in egg powders exposed to oxygen.
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HE investigation described here is a portion of a major project carried on a t this laboratory dealing with the deteriorative changes in stored, dehydrated whole egg powders. As oxygen contributes seriously to the deterioration (6, 8, 14, It?), it was desirable to determine the rate at which the oxygen is absorbed by dried eggs under various conditions. The effect of the moisture content of the eggs on oxygen absorption rate was of special interest. It had already been established that certain nonoxidative changes were retarded a t low moistures ( 4 , 17, 81), but there was no assurance that oxidative changes would be similarly affected. I n fact, experience with other foods, notably cereals, has shown that oxidation of fats is accelerated at low moistures (12, .@). Other variables affecting the rate, that were studied in the present investigation, included temperature, oxygen pressure, mode of preparation, and surface area of the egg powders. MATERIALS AND EXPERIMENTAL METHOD
Measurements were made on three commercial spray-dried whole egg powders (C81R, C77R, and H) and on two powders (LO and L10)prepared in this laboratory by lyophilization.
Sample H was prepared by a special process in which the liquid egg was concentrated to 37.5% solids before being spraydried. It was supplied through the kindness of Geo. Gelman, U. S. Army, Quartermaster Food and Container Institute, Chicago, Ill. The commercial samples were received packed in sealed tinned cans in an atmosphere of nitrogen. Before measurement, the lyophilized powders (in atmosphere of air) were stored in a cold room at 30 C. The specific surface of each egg powder was known from published data based on measurements of nitrogen and argon adsorption isotherms at liquid nitrogen temperatures (20).
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The ox gen absorption measurements were made in constantvolume Jfferential manometers of the Summerson type (86) employing flasks of about 50-cc. capacity with glass-stoppered side arms. A white mineral oil having a density of 0.85 was used as the manometric fluid. All experiments were conducted at constant volume and total pressure of 1 atmosphere. The consumption of oxygen was calculated from the known flask constant and the observed change in pressure. The average change in oxygen pressure during a n experiment was about 0.005 atmosphere. This is equivalent to consumption of 0.25 cc. of oxygen and represents a 5Yo change in the experiment at the lowest oxygen pressure (10% oxygen). Because, in preliminary experiments, some carbon dioxide was found to be evolved during the reaction, 0.1 gram of Ascarite was placed in the side arm of each flask t o serve as an adsorbent for this gas. The actual amount of evolved carbon dioxide was so small that the adsorbent could have been dispensed with in most experiments. Measurements with gas mixtures containing nitrogen or carbon monoxide were made by the differential method (26) against a control flask containing the same gas mixture and Ascarite, but no eggs. Measurements at 100% oxygen, with powders a t different moisture levels, were made by the simpler Warburg method (W), where the reference limb of the manometer is open t o the atmosphere and the readings are corrected for changes in barometric pressure. The results obtained b y this method agreed within 2% with those by the differential method when compared at the two extremes of the moisture range, 0.4and 11.8%. To prepare samples for measurement, 5.0 grams of the stock egg powder of known moisture content (approximately 2%) and 0.1 gram of Ascarite were placed in the reaction flask: the moisture of the powder was then adjusted to the desired value b y placing the flask in a constant humidity chamber for about 2 weeks (until equilibrium had been attained). The equilibration was done at 25" C. in evacuated desiccators (16) containing an appropriate concentration (26) of sulfuric acid. The control flask containing Ascarite was treated in the same manner in order to mdn-
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 40, No. 8
l " " " " l
F i g u r e 1. Absorption of O x y g e n at 24.8" C., f o r LO E g g s at 2 . 2 4 q ~W a t e r
tain the same vapor pressure of water in both flasks. The moisture content of the eggs was established from measurements on duplicate samples in weighing bottles placed in the same humidity chambers and also by direct determination on the material in the reaction flask at the compietion of the oxygen absorption experiment. The two determinations, carried out according t o the A.O.A.C. vacuum-oven method (Z,16),checked to 0.1%. The manometers were filled with the desired gases by evacuation and filling, repeated three times (24). When gas mixtures were used they were first prepared in a separate storage flask (24). Gases used were commercial oxygen, commercial oilpumped nitrogen, and carbon monoxide prepared in the laboratory ( 7 ) . The reaction flasks were immersed, during the measurements, in a water bath maintained a t constant temperature to within *0.01" C., and covered to exclude light. The flasks were not shaken. Equilibration time of about 3 hours was allowed in measurements a t 15' C. and about 1hour at 25 and 35" C. O
EXPERIMENTAL RESULTS
Detailed investigation of the oxidation of whole egg powdei and its dependence on moisture content, temperature, and oxygen partial pressure was made only on the lyophilized, LO, samples. Comparison of the behaviors of the different powders was made only at one moisture level, approximatelv 275, and a t two temperatures, 15.1 ' and 24.8" C. Only initial rates of absorption are reported and except where indicated otherwise, they are expressed in cubic centimeters of oxygen at standard conditions (273" C. and 1 atmosphere) per 1000 grams of solids per hour. They were calculated from the slopes of straight-line plots of volume of oxygen absorbed against time. The total amount of absorption during a measurement was, on the average, about 0.25 cc. of oxygen per &gram sample of eggs, measured with an accuracy of *5%. The results of a typical experiment with LO eggs are shown in Figure 1. The results of two experiments with LO eggs to determine the course of the reaction over a long period of time-one with and one without Ascarite, by the differential method at 35.0" C.are shown in Figure 2, where the decrease in the amount of gas i s plotted against time. From curve I (with Ascarite) i t is seen that the rate decreases with time from the initial value of 1.01 cc. of oxygen per kg.-hr. to a nearly constant value of 0.29 cc. per kg.-hr. a t 2800 hours when 1200 cc. of oxygen per kg. had been absorbed. There is no evidence of an induction period. Curve I1 (without' Ascarite) represents a difference between the oxygen consumed and the carbon dioxide evolved. The amount of carbon dioxide evolved, calculated from the difference of the two curves a t the end of the experiment, amounts to 0.08 mole of carbon dioxide per mole of oxygen consumed. This represents a minimum value for the ratio as the moisture content of the sample with Ascarite contained 0.4% less water than the one without, and the tu-o measurements are not strictly comparable. I n another experiment carried to a stage where 2500 cc. of oxygen were consumed per kg. of eggs, the ratio of carbon dioxide to oxygen was found by gas analysis to be 0.21. These figures, however, do not represent the total amount of
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I 500
1 1000
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2000
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TIME (HOURS1
F i g u r e 2.
Course
of O x y g e n U p t a k e at 35.0' C. for LO Egg Powders
Curve I for eggs at 1.84% HzO measured in the presence of Ascarite represents net amount of oxygen consumed; curve I1 for eggs at 2.257' Hz0 without Ascarite, represents difference between oxygen consumed and carbon dioxide evolved
oarbori dioxide produced in the reaction because a considerable amount of it remains absorbed by the eggs. It is estimated, from unpublished data on adsorption of carbon dioxide on dry eggs, that the total amount of carbon dioxide was approximately twice that observed in the gas phase. Data for the initial rates of oxygen absorption at various moisturelevels and t,hree temperatures, 15.1', 24.8",and 35.0' C., a t 1 atmosphere pressure of oxygen, are given in Table I. The LO eggs were measured over a moisture range of 0.43 to 11.82% water; all other egg powders were measured a t only one moisture level, approximately 2% water. The results a t 24.8' C. were obtained on the same samples as were used at 15.1" C. This is justified because the initial rate of oxygen absorption remains constant (within 2y0) over a relatively long absorption range, 0 to 0.7 cc. of oxygen per 5 grams of eggs, and the rate measurements at 15.1' C. involved an absorption of only about 0.2 to 0.3 cc. per 5 grams of eggs. This was confirmed also by the good agreement ( *lyo)with the result of a measurement on a fresh sample of LO eggs at 24.8"C. at 2.13% water. YARIATIOX O F INITIAL RATE WITH bfOISTURE CONTENT. The data in Table I for LO eggs a t 15.3 ' and 24.8' C. indicate
'FABLE 1. INITIAL RATEO F
OXYGEN
AssoRprrIorj B Y VARIOUS
EGGPOWDERS
(Results a t t atmosphere of oxygen a t various temperatures and moisture levels) Initial R a t e X 102 at, Moisture, Various Temperatures E g g Powder
