INDUSTRIAL AND ENGINEERING CHEMISTRY
350
ACKNOWLEDGMEXT
Vol. 38, No. 3
The authors are indebted to H. L. Fevold for samples used, and wish to acknowledge the interest and suggestions of other members of the staff of this laboratory who are investigating the causes of deterioration of dehydrated eggs.
(6) Edwards, B. G., and Dutton, H . J., Ibid..37, 1131 (1945). (7) Kuhn, R., and Brockrnann H. B E F 65B 894 (1932). (8) Maillard, L.c.,A ~them:, , 5,'258 ; 1 9 1 ~ ; , (9) Miller, E. S., "Quantitative Biological Spectroscopy", Minneapolis, Burgess Pub. Co., 1939. (10) Xat. Bur. of Standards, Letter Circ. 547 (1939). (11) Olcott, H. S.,and Dutton, H.J., IND.EbG. C H E X . , 37, 1119
LITERATURE CITED
(1945). (12) Pearce, J. A., Thistle, M . W., and Reid, M . , Can. J . Research,
0 2 1 , 341 (1943). Balls, A. K., and Swenson, T. L., Food Resewch, 1,319 (1936). (13) Saunderson, J. R., J . Optical SOC.A m . , 32, 727 (1942). Boggs, M. M., and Fevold, H. L., unpublished results. Best, L.R., and Lome, B., Proc. I n s t . Food Tech., Dutton, H. J., Bailey, G. F., and Kohake, E., ISD.ENG.C H ~ M , , (14) Stewart, G . F.,
35, 1173 (1943).
1943, 7 7 .
Dutton, H. J., and Edwards, B. G., ISD. ENG.CHEM.,37,
1123
(1948).
Dutton, H. J., and Edwards, B. G., ISD.ENG.CHEM.,ASAL. ED.,18, 38 (1946).
(15) (16)
u. s. D W . k-., C b c . 583, 57 (1941).
Western Regional Research Lab., unpublished results.
(17) White, W. H., and Grant, G. A., Can. J . Research, F22, 73 (1944).
SPecific Heats of Vegetable Oils from 0"to 280" C. PAUL E. CL>4RK, C. R. WALDELAND, AND ROBERT P. CROSS Washington and Jefferson College, Washington, Pa.
T h e specific heats of hjdrogenated cottonseed, castor, soybean, tung, linseed, and perilla oils have been determined otcr the temperature range 0 ' to 280" C. in a batch calorimeter. For each run the specific heat w a s calculated from measurements of the weight of the oil, the actual temperature rise of the oil, and the heat energy supplied to the oil corrected for the heat capacitj of the calorimeter. The heat capacity of the calorimeter was determined at various temperatures by liquid diphenyl. Within the temperature range studied, the specific heats of each oil increase with increasing temperatures arid all values fall within the range 0.40 to 0.70 calorie/gram/ ' C. In general, the specific heat-temperature curiea for the different oils hale about the same shape and slope and are displaced toward lower value6 as the iodine numbers of the oils increase. The values are compared with those of other intestigators.
T
HE lack of adequate specific heat data in the literature for vegetable oils and the importance of such data in industry, as well as in phase studies of fats and oils, were discussed recently by Gudheim (4) and Bailey, Todd, Singleton, and Oliver (I). Specific heats of the various types of vegetable oils may also be of value in studying the mechanism of the heat-induced polymerization of drying oils. Deaglio and b4ontu ( 2 ) used a n electrical comparison method, and reported the specific heat of castor oil as 0.505 a t 50" C. and 0.525 a t 70". Long, Reynolds, and Kapravnik (5) reported the specific heats of alkali-refined linseed oil (iodine number, 181.3) as 0.504 to 0.665 in the range 75" t o 290" C.; tung oil (iodine number, 156.7) as 0.516 to 0.644 in the range 69" to 155' C.; and soybean oil (iodine number, 131) as 0.568 to 0.765 in the range 75' to 287" C. Their apparatus consisted of an insulated thermos flask used as a batch calorimeter. They calculated specific heats from a measured amount of heat energy supplied to a known quantity of oil and the actual temperature rise of the oil. They stated that their results are reasonably correct in the lower temperature ranges,and that the heat capacity is a linear function of temperature in the lower ranges from 70" to about 170" C. Delaplace (3) used the method of mixtures, and reported
specific heats of castor oil as 0.424 to 0.553 in the range 0" t o 210" C. Gudheim (4)also used the method of mixtures and reported the specific heats of refined cottonseed oil as 0.524 * 0.010 in the range 45' to 50" C., and 0.535 * 0.010 in the range 95' to 100' C., and refined and bleached palm oil as 0.515 * 0,010 in the range 45" to 50" C. Bailey, Todd, Singleton, and Oliver (1) used a n all-metal batch calorimeter of special design for low-temperature determinations with which they obtained results accurate within 1%. With the same apparatus they also reported (8)specific heats of cottonseed oil (iodine number, 108.3) as 0.471 to 0.499 in the range 15' to 60" C., and of hydrogenated cottonseed oil (iodine number, 59.5) as 0.497 to 0.514 in the range 40" to 70" C. Oliver and Bailey ( 7 ) used the same apparatus and reported the specific heats of highly hydrogenated cottonseed oil (iodine number, 0.85) as 0.524 to 0.537 in the range 67" to 82" C. The purpose of the present study was to determine specific heats of various types of vegetable oils over much of the temperature range in which they are commonly heated in industry. To obtain uniformly good results in the range 0' to 280" C., a modification of the apparatus and technique employed by Long, Reynolds, and Napravnik (5)was used. All oils were furnished by the Armstrong Cork Company. Before use they were heated in a round-bottom flask maintained a t 100" C.for 3 to 6 hours under a pressure of 2-3 mm. of mercury to remove moisture. After this heating their iodine numbers (Wijs) were as follows: hydrogenated cottonseed, 6.5; castor, 83.0; soybean, 128.3; tung, 154.4; linseed, 172.1; perilla, 186.2. The diphenyl used in determining the heat capacity of the calorimeter was Eastman Kodak Company's highest purity, melting point 69.5-70.5' C. APPARATUS AND PROCEDURE
The calorimeter was a silvered, evacuated Dewar flask of about one liter capacity, closed with a gasketed '/r-inch brass plate equipped with four brass tubes for heater leads, thennometer, motor-driven glass stirrer, and inert gas conduit. The gasket was a ring of either '/:-inch gasket cork or 1,'a-inch synthetic rubber. The brass tubes were about 3 inches long, had an inside diameter of about 3/8 inch, and were brazed to the brass plate.
March, 1946
b
INDUSTRIAL AND ENGINEERING CHEMISTRY
A======$
Figure 1. A . Inert
Apparatus for Specific Heat Determination F. Thermometer G.Thermoregulator H . Electric heaters I . Metal base J . Steel bolt
gaa inlet
B . Leads to voltmeter, ammeter, and battery C. l/&nch brasa plate D . Gasket E . Platinum wire heater
An oil-tight seal was made by bolting the brass plate and gasket securely in position by four l/rinch steel bolts (Figure 1). The calorimeter was immersed in the liquid of a constant temperature bath in such a way that the brass tubes extended about
351
1.5 inches above the surface of the bath liquid. The bath liquid, contained in a 12 X 12 inch Pyrex jar, was water for tempera- , tures below 60' and hydrogenated cottonseed oil for higher temperatures. Two 1500-watt heaters and a thermoregulator (with relay) were used to control the bath temperature to 1.0.2' C. The heater in the calorimeter was a platinum wire, B. & S. gage 25, of approximately one ohm resistance and was totally immersed in the oil. The copper leads, which were fused t o the heater, were brought out through cork insulation in one of the outlet tubes. The platinum wire was heated with direct current from a storage battery. A voltmeter was connected across the heater terminals with an ammeter in series. A thermometer, with bulb totally immersed and extending through one of the brass outlet tubes, was used to measure the temperature of the oil. To cover the temperature range, four thermometers, with I/(' C. divisions, manufactured by ,the H-B Instrument Company, Inc., were used. A cathetometer was employed in reading the thermometers. The stirrer was constructed from a 4-mm. glass rod and extended through the center outlet tube. The inert gas conduit was a 6-mm. glass tube which extended through the fourth outlet tube t o a depth of about 1 cm. below the brass plate. A sample of oil weighing 250 to 450 grams was placed in the Dewar flask, and the gasketed brass plate, fitted with stirrer, thermometer, and resistance heater, was bolted in position. This assembly was immersed to the proper depth in the liquid of the constant temperature bath. The stirrer was started, the heater leads were connected, and a steady stream of dry nitrogen was passed through the conduit into the flask.
0.70 TUNG OIL IODINE NO,:154.4
0.60
0.60
'0.50
0.50
. 2 . w $
0.40
I
X X
0.40
I
0.7C
0.70
W
UJ
CASTOR OIL IODINE NO.: 83.0
0.60
0.50
E
0.40'
I
I
I
I
I
I
I 0.40
0.70
0.60
0.50
I20 160 TEMPERATURE,
Figure 2.
0 this paper;
200 o r
E40
0.40 280 0
40
80
I20 160 TEMPERATURE, 'C.
200
240
280
Specific Heat-Temperature Curves foq Vegetable Oils
+
X Long et 01.; Dela laces A Deaglio and Montu, A refined oattonseed oil Gudheim; 0 highly hydrogenated cottonseed o i l Oliver and%dleyt hydmganated cottonseed oil, Oliver et al.; dcottonseed oil, Oliver et al.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 38, No. 3
T h e determination of t h e TABLE I. SPECIFIC HEATVALUES OF VEGETABLE OILS (CAI,ORIES/GRAJI/o c.) specific heats for a given sample Hydrogenated of oil consisted of a series of inCastor Oil Soybean Oil Tung Oil, Cottonseed Oil, Iodine No. 6.5 Iodine No. 8h.O Iodine No. 128.3 Iodine No. 154.4 Linseed Oil, Iodine No. 172.1 dividual runs, each of which !?as SP. SP. SP. SP. SP. SP. carried out a t a temperature C. heat C. heat C. heat C. heat C. heat C. heat IO' C. or more higher than the 29.9 0.495 79.6 0.520 1 . 2 0.448 21.5 0.435 30.2 0.463 160.0 0.538 39.6 0.514 100.2 0.533 19.7 0.468 37.3 0.463 39.9 0.476 160.3 0,552 preceding one without disman47.7 0.510 119.8 0.544 38.6 0.469 68.7 0.479 47.8 0.458 170.0 0.555 tling t h e a p p a r a t u s . During 61.5 0.519 140.3 0.544 60.9 0.479 69.0 0.488 6 0 . 8 0.482 l i 0 . 6 0.550 70.0 0.547 160.4 0.570 70.5 0.490 79.3 0.486 61.2 0.491 180.5 0.547 each run the oil in the calorim70.4 0.534 201.4 0.584 80.4 0,493 90.1 0.500 70.2 0.505 181.0 0.556 79.8 219.4 0.595 0.539 90.4 0.504 99.9 0.502 70.7 0.491 181.0 0.561 eter was heated through a 90.4 0.550 250.1 0.638 100.4 0.508 109.7 0,513 80.2 0.508 190.6 0.548 100.1 0.548 110.0 0.521 120.5 0.515 temperature interval of about 4". 270.3 0.643 8 0 . 5 0.485 191.1 0.554 110.6 0.557 110.5 0.521 129.7 0.513 80.5 0.487 198.9 0.559 Before the run was started, the 120.9 0.565 120.8 0,527 90.2 0.517 130.7 0.517 200.1 0.558 130.3 0.563 Perilla Oil, 130.9 0,526 140.1 0.525 90.8 0.501 208,7 0.572 oil was heated electrically to a 131.2 0.562 141.3 0.531 Iodine No. 186,2 210.2 0.570 150.2 0.529 100.2 0.515 141.2 0.568 151.5 0.540 160.3 0.535 219.1 0.565 100.4 0.504 temperature about 2' below the 152.1 0.576 6 . 4 0.414 161.9 0.550 170.6 0.548 220.0 0.580 110.1 0.518 expected average of the tem162.5 0,570 19.3 0.421 172.3 0.558 180.5' 0.565 110.4 0.510 239.9 0.605 172.4 0.588 26.9 0.436 182 7 0.567 240.1 0.591 182.0 0.539 120.2 0.518 perature interval and the heat 182.7 0.585 19.9 0.454 249.9 0.611 193.3 0.579 190.6 0.549 120.3 0.521 192.3 0.579 151.5 0.481 200.1 0.594 192.8 0.541 250.4 0.612 130.3 0.518 was turned off. To start the 193.3 0.575 199.6 0.515 209.6 0.590 260.3 0.619 198.8 0.549 130.3 0.525 200.2 0.589 run, temperature readings were 270.4 0.575 260.5 0.592 210.0 0.607 200.3 0.566 140.1 0.532 209.8 0.603 219.5 0.581 260.5 0.606 140.7 0.525 taken every minute for 4 or 5 219.7 0.595 219.9 0.598 150.2 0.537 270.5 0.636 240.2 0.633 240.2 0.617 '270.7 0.643 150.6 0.534 minutes to determine the rate of 240.3 0.626 250.5 0.621 250.7 0.633 260.8 0.649 temperature change. This rate 260.9 0.622 271.3 0.666 was small and nearly constant. 269.3 0.655 271.2 0.657 Then the oil was heated for 3 or 4 minutes, the time being accuratelymeasured by a stop watch; TABLE 11. I O D I N E NUMBERS AND RELATIVEVISCOSITIES OF VEGETABLE OILS BEFORE AND AFTER SPECIFICHEAT ammeter, voltmeter, and temperature readings were taken each DETERMINATION minute. Heating was then discontinued, but the temperature of the oil continued to rise for few seconds until a maximum was AY. Viscosity AY. Iodine KO. a t 25' C., Sec. reached. Thus the number of seconds that elapsed from the time Oil Before After Before After the heat was turned on until the temperature of the oil reached a Hydrogenated cottonseed 6.5 6.5 maximum (time for maximum temperature) was only a few secCastor 83.0 95.6 Soybean 128.3 124.9 onds more than the actual heating time. Temperature readings Tung 154.4 gel Linseed were again taken each minute for several minutes to determine 172.1 157.9 Perilla 186.2 167.0 the rate of temperature change. Again this rate was small and nearly constant. To minimize heat losses, the bath temperature was kept a t the expected average of the temperature interval for the run. Then The heat capacity of the calorimeter was calculated by subthe oil in the calorimeter and the liquid bath were heated to the stituting the experimentally determined valucs in thc following proper temperatures for the next run. Usually about 30 minutes equation : elapsed between runs, and the total time for a determination varied from 6 to 14 hours, depending on the number of runs in the volts x @wt.diphenyl, X determination. actual temp. rise X heat capacity The heat capacity of the calorimeter was determined over the - sp. heat of d i p h e n y l of calorimeter, = temperature range 80' to 200" C. by the procedure described tal./" C.) actual temp. rise except that the oil was replaced by liquid diphenyl, the specific heat of which was known. Heat capacity values of the calorimThe actual temperature rise was calculated by the method exeter outside this range were obtained by extrapolation. plained above. The specific heat values used for liquid diphenyl were calculated from the equation reported by Newton, Kaura, METHODS OF CALCULATION and De Vries (6). The specific heats of the oils were calculated by substituting the experimentally determined values in the following equation: RESULTS AND DISCUSSION O
O
(
)
heat of oil, (sp.cal./g./oC.) )=
x
actual temp. rise x heat capacity of calorimeter wt. of oil X actual temp. rise
volts
The difference between the temperature of the oil a t the instant the heat mas turned on and the maximum temperature obtained after the heat was turned off, both thermometer readings being corrected for stem exposure, was the apparent temperature rise. The actual temperature rise was obtained from the apparent temperature rise by adding or subtracting a correction. This correction was calculated as the product of the "time for maximum temperature" and the average rate of temperature change before the heat was turned on and after the maximum temDerature was reached.
The specific heats of hydrogenated cottonseed, castor, soybean, tung, linseed, and perilla oils are given in Table I and represented graphically in Figure 2. Actually these are average values for the temperature interval of a run, but since this interval is small (about 4'), they may be assumed to be the specific heats a t the mean temperatures of the intervals. The authors estimated that these values represent the specific heats of the oils within 2.5% over the entire temperature range 0' to 280' C. Table I1 gives the average iodine numbers and relative viscosities of these oils before and after a determination. I n general, the specific heat-temperature curves for the different oils have about the same shape and slope and are displaced toward lower values as the iodine numbers of the oils increase. The specific heats of highly cottonseed oil., hydro- - hydrogenated genated cottonseed oil, and cottonseed oil, as reported by Oliver, ~
March, 1946
INDUSTRIAL AND ENGINEERING CHEMISTRY
Bailey, and cc-workers ( 7 , 8 )and plotted in Figure 2 for comparison, appear to show the same tendency. The values reported in Table I1 seem to indicate that the drying and semidrying oils polymerized to some extent as a result of the heat treatment received during a determination, since their iodine numbers decreased and their viscosities increased. These properties changed in the opposite direction or remained the same for the nondrying castor oil and hydrogenated cottonseed oil. Tung oil began to body noticeably while being heated at about 200” C. after the determination had progressed for about 8 hours, and gelled soon afterward with continued heating. The specific heat values of castor oil are in good agreement with the two values reported by Deaglio and Montu (9)but are consistently a little higher than those determined by Delaplace (3) as shown in Figure 2. The specific heat values reported by Long and co-workers (6) for soybean and tung oils are consistently higher than those given in this paper. They reported values for alkali-refined linseed oil which agree fairly well with those in this paper except that their values are considerably higher in the range 190” to 270’ C. (Figure 2).
353
ACJLNOWLEDGM ENT
The authors take pleasure in expressing their indebtedness to the Armstrong Cork Company for financial assistance which made this work possible, for permission t o publish this paper, and for furnishing the oils and gasket materials. Appreciation is also expressed for the assistance of Harold E. Adams of Armstrong Cork Company for furnishing the values in Table I1 and for advice and many helpful suggestions. LITERATURE CITED
(1) Bailey, Todd, Singleton, and Oliver, Oil & Soup, 21,293 (1944). (2) Deaglio and Montu, 2. tech. Physik., 10, 460 (1929). (3) Delaplace, Reni, Contpt. rend., 208, 515 (1939). (4) Gudheim, A. R., Oil & Soup, 21, 129 (1944). (6) Long, Reynolds, and Napravnik, IND. ENG.CHSM., 26, 864 (1934). (6) Newton, Kaura, and De Vries, Ibid., 23, 35 (1931). . (7) Oliver and Bailey, Oil & Soap, 22, 39 (1945). (8) Oliver, Singleton, Todd, and Bailey, Ibid., 21,297 (1944).
LINSEED PROTEINS.
..
Alkali Dispersion and Acid Precipitation Information and data are given for the isolation of linseed protein by alkali extraction and acid precipitation. The flaxseed hulls contain a mucilage which interferes with the settling of acid-precipitated protein. Methods for the decortication of the linseed meal and analytical information on the composition of the hulls and embryo fractions are given. The amount of nitrogenous matter which can be dispersed within a wide range of p H values from the decorticated and undecorticated linseed meal is presented. The pH value of maximum nitrogen precipitation is determined, and protein yields are estimated.
F
LAXSEED has been an important crop (11) in our country since pioneering days, and in recent years the United States has ranked fourth among the nations of the world in flaxseed production. The peak year for United States flaxseed production, over an extended period prior to the war, was in 1924 with a record of 31 million bushels; the trend then became downward with a low of 5 million bu+els in 1936. The war economy revised this trend so that more than 50 million bushels were pr’oduced for 1943. Furthermore, the domestic supply of flaxseed is normally supplemented by importations. While the composition of flaxseed varies considerably with climatic conditions (S),the oil content on a moisture-free basis is.about 40 to 43%. The commercial linseed meal containing several per cent of oil is sold at Minneapolis on a 34% protein basis; however, the solventextracted meal, when moisture-free, contains 40 to 49% protein (1, 6). Although t h e oil has sold at 8 to 12 cents per pound at Minneapolis, the oil meal has brought only 1.25 t o 2.25 cents per pound. Thus, on the basis of their abundance’and low cost, the linseed proteins are entitled t o serious consideration in a research program directed toward the development of vegetable proteins for industrial utilization. Of the two principal linseed products, the oil has always held the major share of scientific attention because of its great importance as a drying oil. I n the field-of protein research the‘only investigation of importance concerned with the isolation and identification of linseed protein is the classical work of Osborne (7) in 1892. Osborne,
A. K. SMITH, V. L. JOHNSEN, AND A. C. BECKEL Northern Regional Research Laboratory, of Agriculture, Peoria, I l l .
U. S . Department
working principally with his salt-extraction technique, showed that “the extracts of the flaxseed contain a globulin precipitated by dialysis, a proteid, resembling both globulin and albumin, precipitated by long-continued heating at 100 ” C., as well as by sodium chloride in the presence of acid; proteose and peptonelike bodies, and a proteid not extracted by sodium chloride solution, but soluble in dilute potash-water”. He described the dialyzed globulin as forming octahedral crystals. I n regard to the peptones, Osborne concluded that “they are wholly formed during the extraction and separation”; this suggests the presence of a proteolytic enzyme in the linseed dispersions. The globulin was found to contain 18.6% nitrogen; the albuminlike body, 17.7% nitrogen. Ohe sample of the proteose contained 18.78% nitrogen; another contained 18.33%. From these values and estimated quantities of protein for each fraction, he arrived at a nitrogen-protein conversion factor of 5.5. The work of the few investigators (8,9, 10) who have worked on linseed proteins since the time of Osborne has been limited to studies on salt peptization. The salt extragtion and dialysis methods heretofore used for isolating flaxseed proteins are not well suited for large-scale operation, since the dialysis of the protein dispersions and recovery of the salts are time consuming. The present investigation explores the possibility of isolating the protein by the method of alkali extraction and acid precipitation similar to that described for the isolation of soybean protein (a, 8). REMOVAL OF HULL AND MUCILAGE
Preliminary studies on protein isolation showed that the mucilage, which occurs in the flaxseed hull in relative abundance, seriously interferes with the settling of the precipitated protein.
.
