July, 1934
INDUSTRIAL AND ENGINEERING
flash-pasteurized as described in this paper. The results, although somewhat erratic showed a tendency toward a slight diminution (about 1.0 cc.) in reducing power after 9 months of storage a t room temperature. Further work along this line is Contemplated this season. SUMMARY
A method is described for preserving orange juice by slowly reaming the halved fruit, immediately deaerating, pasteurizing a t about 96" C. (205" F.) for not more than 5 seconds, filling into the containers a t 76" to 82" C. (170" to 180" F,), and vacuum-sealing a t a pressure sufficiently high to prevent boiling. Juice thus prepared has been stored for 10 months a t 16" C. (60" F.) and still has a satisfactory aroma and taste. The addition of sugar sirup to increase the ratio of total soluble solids-total acidity to 15.0, and terpeneless orange oil to the extent of 0.003 to 0.005 per cent, has been found to enhance the keeping qualities of the juice. Orange juice, packed as described in this paper, will not retain a satisfactory aroma and taste for mort? than about 3 months if stored a t temperatures in the vicinity of 32" C. (90" F.). Florida Pineapple, Seedling, and Temple oranges, if of the proper maturity, make as satisfactory a pack as Florida Valencias. "Sweated" fruit, or that which has been through the coloring rooms, or has stood in the packing house for more than a week does not make a satisfactory pack. Fruit of 10tv acidity is unsuitable for canning.
CHEMISTRY
773
Packs in glass darken especially in the absence of significant amounts of tin and if stored a t temperatures of 27" C. (80" F.) or higher. During storage at temperatures of 32" to 38" C. (90" to 100" F.) there is an increase in reducing sugars (as invert), a corresponding decrease in nonreducing sugars (as sucrose), and a decrease of pH, but there is no change in titratable acidity. Although results were somewhat erratic, orange juice preserved as described in this paper showed a slight diminution in reducing power toward dichlorophenolindoplienol. LITERATUBE CITED (1) (2) (3) (4) (5) (6) (7)
(8) (9) (10)
Bennett, A. H., and Tarbert, D. J., Bzochem. J.,27, 1294 (1933). Chace. E. XI.. Calif. CitrooruDh. 5. 264 (1920). ' Coons, B. C.,'Canking 14,275 (1933). Cruess, TV. V., Calif. Agr. Expt. Sta., Bull. 244, 157 (1914). Fellers, C. R., and Isham, P. D., J. H o m e Econ., 24, 827 (1932). Hanke, M. I., "Diet and Dental Health," g . 36, Univ. Chicago Press. 1933. Irish, J,' H., Calif. Agr. Expt. Sta., Circ. 313 (1928); revised by W.V. Cruess, 1932. Joslyn, M. A., and Marsh, C. L., Food. Ind., 5, 172 (1933): Canning Age, 14, 229 (1933). McDermott, F. A,, J. IXD. ENG.CHEM., 8, 136 (1916). Fla. Agr. Expt. Sta., Bull. 135, 130 (1917). Mottern, H . H., and von Loesecke, H. W., Fruit Product8 J., 12, 325 (1933); Bnonymous, Glass Pucker, 12, 551 (1933).
Ah,
RECEIVED .4pril 2, 1934. Presented as p a r t of the joint Sympoaiurn on Citrus Fruits before the Divisions of Agricultural and Food Chemistry a n d of Biological Chemistry a t the 87th Meeting of the American Chemical
Society, St. Petersburg, Fla., March 26 t o 30, 1934. search Division Contribution 219.
This paper is Food
Re-
Effect of Respiration on Vegetable Flavor E. F. KOHMANAND N. H. SANBORN, National Canners Association, Washington, D. C.
A
S A RESULT of the known
susceptibility of vitamin C correlated is available. Data have been presented elsewhere to oxidation, great care to eliminate atmospheric (3) showing that rough treatment resulting in bruising of oxygen is customary among those engaged in proc- peas and lima beans may be the cause of abnormal flavors essing foods. It is not always realized that each raw vege- in these vegetables after canning. While it was shown that table and fruit has a normal oxygen requirement. If con- the rough treatment in question was generally followed by ditions of h a n d l i n g are such the usual tendency of slightly that the vegetable cell is not increased carbon dioxide Bruising of vegetables has a marked effect on able to secure its normal quota e v o l u t i o n , t h e bruising was respiration. Oxygen consumption is greally of oxygen or if the treatment s h o w n t o be the cause of a reduced iahile carbon dioxide ecolution generally is such that the functioning of marked decrease in oxygen conincreases although, contrary to the usual opinion, the cell to use its normal quota s u m p t i o n . It has long been it m a y under certain conditions decrease but of oxygen is disturbed, results known that, if the oxygen supply quite as disastrous as oxidation of a vegetable or fruit is limited, not to the same degree a s the oxygen consumpof vitamin C may follow. I n c o h o l and acetaldehyde are a1 tion. I n this connection, raw frozen vegetables other words, abnormal reducing formed as a result of anaerobic m a y be considered to be severely bruised since fhe reactions or conditions may be as respiration. I n the case of the cells are generally ruptured. An explanation undesirable as abnormal oxidizb r u i s e d peas and lima beans is thus afforded for the off--flavors that develop. ing conditions or reactions. referred to, the f o r m a t i o n of I n the normal respiration of a alcohol and acetaldehyde was Alcohol and acetaldehyde are produced in bruised vegetable, the ratio of oxygen demonstrated, b u t it was eegetables apparently as a normal product of c o n s u m e d to c a r b o n dioxide shown that these were not the anaerobic respiration. These products, however, evolved is close t o unity. Gencause of the off-flavors noted. do not account f o r the off-flavors that develop erally, in b r u i s e d o r i n j u r e d Evidence was presented, howeither in vegetables in which artificial anaerobic vegetable tissue there is a tendever, to indicate t h a t the offency toward increased carbon flavors were a p r o d u c t of anrespiration has been induced or in bruised or d i o x i d e e v o l u t i o n , but, a s aerobic respiration. raw frozen vegetables. T h e manner in which this will be shown, this is not alThe possibilities of anaerobic anaerobic activity is involved in the freezing, ways the case. Little informaactivity a f f e c t i n g t h e flavor refrigeration, and handling of vegetables and tion in w h i c h b r u i s i n g and of various vegetable products fruits is discussed. oxygen consumption have been as a result of t h e m a n n e r of
174
INDUSTRIAL AND ENGINEERING CHEMISTRY
handling is far-reaching. Further data, selected from many experiments conducted over a period of several years, are presented here to show additional applications of the consequences of anaerobic activity.
EXPERIMENTAL PROCEDURE Respiration experiments were conducted in a battery of units sketched in Figure 1: These were held in a water bath to insure against air leakage and to maintain a constant temperature. To place the vegetables in the experimental jar, C, without their coming in contact with the alkali in the bottom, they were held in wide-mesh mosquito netting bags which were set upon glass stands in the bottom of the jar. The size of sample usually was 200 grams and the duration of the test 5 hours. The volume of jar C was one liter.
w
most easily be preserved for analysis. The percentage of volatile material was calculated back to the raw product. To the contents of a No. 2 can (approximately 575 grams), 250 cc. of water were added; the mixture was saturated with sodium chloride and 250 cc. were distilled over a sand bath. The distillate was again saturated with sodium chloride and redistilled to obtain 50 cc. With corn the refractive index and specific gravity of this distillate were in close agreement, based on the assumption of its containing only ethyl alcohol. I n the case of peas, the two did not agree as well. I n the case of each vegetable i t was possible to identify the presence of acetaldehyde in the distillate in small amounts by preparing in p u r s e d form, for a mixed melting point, the dimethylcyclohexanedione derivative. I n the controls of the various experiments-that is, with vegetables that received no abnormal treatment-the volume of oxygen and of the carbon dioxide are not far from equal, a condition that follows the complete oxidation of sugar with gaseous oxygen. I n many experiments duplicate determinations were made with satisfactory agreement between the results. It is not believed that any appreciable carbon dioxide resulted from microbial activity because in many experiments the respiration was studied for a second period sometimes as long as 17 hours, always with a very marked reduction in carbon dioxide evolution. Peas and lima beans whose skins were broken by the bruising process were discarded. This is done with a certain degree of efficiency mechanically in canning, and in these experiments the tendency for microbial infection was thereby lessened.
FIGURE 1. BATTERY OF UNITSFOR RESPIRA. TION EXPERIMENTS
After introducing the product to be studied into C, connection was made with the Erlenmeyer flask, A , through the water trap, B, at the junction, F , without releasing the screw clamp that closed this junction. Previously flask A had been filled with oxygen to a pressure slightly greater than atmos heric. This excess pressure was now released at junction E and t i e leg, D, serving to prevent escape of oxygen due to agitation of the water while setting up the other units, was inserted. Then the screw clamp at F was released. If it was desired to hold the vegetable in an atmos here of oxygen, the air in jar C was first driven out through a fouble-hole stopper by a stream of oxygen before making the above connection. Erlenmeyer flask A was held down to a weighted board by means of a clamp made of spring wire; jar C was held in place by a wire frame but, because of its perpendicular sides, was held down by means of a heavy rubber band. The oxygen consum tion was obtained by measurand calculated to standard ing the water drawn into flask pressure. The volume of carbon dioxide, absorbed by 25 per cent sodium hydroxide, was calculated to the same pressure and to the temperature of the experiment from a double titration of the sodium hydroxide in the bottom of flask C, using phenolphthalein as indicator for the first titration and methyl orange for the second. While the humidity in flask A was probably 100 per cent, no correction was made for this, as it necessitated a knowledge of the humidity in jar C at the beginning and end of the experiment. The error is of little significance. To freeze a product for respiration studies, it was placed in a narrow tin plate container which held the individual pieces in a single tier and out of contact with the ice and salt solution mixture which constituted the freezing medium. Immediately after rapidly freezing in the time noted, each lot was placed in running water approximately 5 minutes at room temperature for rapid thawing and to bring the vegetable back to room temperature. Controls were held in water for a similar period. All were then thoroughly dried by rolling on absorbent paper or towels, and placed in the respiration chamber. Because of the short time during which the vegetables were held in the frozen state and because they were brought back t o room temperature before introducing into the respiration chamber, it is believed that the volume of carbon dioxide evolved represents that formed during the respiration period, uninfluenced by carbon dioxide that might have accumulated during the short freezing period.
1
Alcohol and acetaldehyde were determined on the products after canning because, by canning, the vegetables could
Vol. 26, No. 7
DISCUSSION OF RESULTS Previously published data (3) and Table I show that bruising has a marked effect on reducing the amount of oxygen absorbed and generally increases in a small measure the carbon dioxide evolution. The bruised, macerated tissue is undoubtedly less porous than sound vegetable tissue since the cell contents of the ruptured cells would tend to fill intercellular spaces. These results, then, may be explained logically by assuming that the ruptured vegetable cell may give off carbon dioxide a t a n increased rate, possibly without gaseous oxygen being involved, and that the macerated area of vegetable tissue acts as a barrier t o the penetration of oxygen to the sound tissue underneath, which consequently undergoes anaerobic respiration. TABLEI. EFFECTOF BRUISING ON PEAS BY DROPPING 35 FEET (10.7 METERS)ON HARDSURFACE OzCorrSUMED PER
TREATMENT
KQ. PER HR.
cc.
ETHYL ALCOHOL
BY
COa
EVOLVED refracPEE KQ. TOTAL tive
By
PERHR.
SUQAE
index
sp. gr.
cc.
%
%
%
FRESHLY H A E V I B T E D , I A E L Y BIRD PEAU H E L D A T 26'
Control I n air 5 hr unbruised I n air 5 h?., dropped 3 times I n 02 5 hr., unbruised I n 0 2 5 hr., dropped 3 times
...
Calc. from anaerobic
CO, %
C.
380
377
4.30 3.30
0.06 0.03 0.02 0.01
... ...
112 554
220
3.61 2.33
0.17 0.07 0.03 0.02
0.097
580
298
386
2.64
0.15 0.07
0.088
...
...
FRESHLY HARVESTED, PRINCE OF WALER P E A S H E L D AT 27' C.
Control I n air 5 hr., unbruised I n air 6 hr., dropped once I n air 5 hr., dropped twice In On 5 hr., unbruised I n 0 2 5 hr.. dropped once In 0 2 5 hr., dropped twice
4i6
. .,
480
5.65 4.72
248
476
..
153 664
475 670
4.93 4.07
649
665
..
510
645
4.53
Lost
Lost
..
..
0.02 0.01 0.22 0.20 0.03 0.02
..
..
0.10 0.08
.... .. ... 0.26
...
... 0.12
Contrary to the generally accepted opinion that a bruised or injured cell always evolves carbon dioxide at an increased rate, bruising sometimes results in a decrease in carbon di-
July, 1934
INDUSTRIAL AND ENGINEERING
oxide evolution. For example, there was decreased carbon dioxide evolution in the Early Bird peas in Table I. These mere severely macerated internally because of their succulence. A raw vegetable, after freezing and thawing, may be regarded as completely bruised since no doubt the cells are fairly generally ruptured. Table I1 shows that there is generally a decreased evolution of carbon dioxide resulting from the freezing treatment, although this reduction is far less than the reduction in oxygen consumption. Further studies are desirable to establish the factors which are responsible for these fluctuations in carbon dioxide evolution as a result of bruising.
CHEMISTRY
715
Refugee beans suggesting alfalfa hay. In the case of peas and lima beans, there is a strong suggestion of incipient putrescence. Joslyn and Marsh ( 2 ) speak of the tendency in peas to develop a particularly strong haylike flavor, but they do not bring out this different character of the flavor.
PRACTICAL APPLICATION There are many instances where the phenomena cited assume practical importance. As pointed out in the 1928 report of this laboratory (4) and subsequently confirmed by others (1) and by commercial experience, vegetables can be successfully frozen only after the enzymes are inactivated. The reason seems to lie in the effect of freezing on the exchange of oxygen and carbon dioxide. TABLE11. EFFECTOF FREEZING ox OXYGENCOXSUMPTION AND CARBON DIOXIDEEVOLUTIOS AFTER THAWING It is recognized in the canning industry that a freshly 01CONWJMED COz EVOLVED pulled load of sweet corn, unless spread in a thin layer, will, P E R KO. P E R KG. if held too long, develop flavors observed in an exaggerated TRWATMENT PER HR. PER H R . CC. cc. degree in the corn represented in Table 111. The effect of WABHINQTON Y A R K B T PEAB F R O M CALIFORNIA HBLD A T 27' C. bruising peas and lima beans by rough handling has already 419 Lost Control been noted. I n this instance the off-flavor developing has Not completely frozen, 5 min. at -18' C. 326 309 Frozen 20 min. at -18' C. 49 333 long been mistakenly ascribed to the vine juice and weed FRESHLY HARVESTED, PRINCE OF WALES PEAB HELD AT 18.5' C. juice with which the peas come in contact in the vining process. 396 445 Control Frozen 40 min. at -20° C. 60 375 When it becomes necessary to hold shelled peas for a more Contro1,in 0 2 44 1 520 165 460 Frozen in Oz 40 min. at -20' C. extended period than usual, cold water offers a convenient refrigerating medium and prevents heating that takes place QREBN REFUOWE B E A N S HARVESTED PREVIOUS DAY, HELD AT 21' C. when the peas are held in the usual lug box. The con166 146 Control 95 Frozen 25 min. at -20' C. 50 venience of this refrigerating medium, however, must be dispensed with because of the abnormal flavors resulting from The similarity between the off-flavors developed i n bruised anaerobic respiration. Pea canners have noticed a poorer vegetables, in raw frozen vegetables, and in vegetables flavor in their products on wet days than on dry. The held under anaerobic or semi-anaerobic conditions, is sug- natural wetness of the vines results in more or less moisture gestive, indicating that anaerobic activity in bruised tissue clinging to the shelled peas. Each drop of water induces is primarily a n anaerobic respiration. This view is not en- anaerobic respiration in the segment of the pea underneath tirely in agreement with Tressler ( 5 ) , who states that most it. enzymic changes in frozen foods are either oxidative or hyAttempts have been made to receive tomatoes at canning drolytic in nature and who ascribes loss in flavor largely to factories in a large vat of water since it affords both a cushion atmospheric oxygen. Since vegetables are not frozen com- to prevent breaking in handling and it is also a convenient mercially except after precooking, atmospheric oxygen is first step in removing dirt. Moreover, well-ripened tomaprobably the chief cause of loss of flavor in them but not toes remain more sound and are better protected held in through enzymic changes. Fruits, however, frozen com- water than in the usual market basket when it becomes mercially in the raw state also suffer deterioration rapidly necessary to hold tomatoes overnight a t a canning factory. after thawing, with flavors comparable to those resulting The results of anaerobic respiration, however, preclude such from bruising or maceration. Since oxygen consumption procedure. is below normal under these conditions, it seems illogical to The result of anaerobic respiration may manifest itself ascribe loss of flavor to atmospheric oxygen. Confirming almost daily in every household. To cite an example, freshly this, hermetically sealing raw frozen vegetables and fruits picked red raspberries in excess of the amount that could be under vacuum has been found not to prevent the develop- used immediately, were kept under ideal refrigeration in an ment of off-flavors. electric refrigerator in a well-filled can with a tight cover. After 24 hours the fragrance and aromatic flavor were markedly spent, although the berries were unchanged in firmness TABLE111. VOLATILE MATERIAL FROM CORN and general appearance. To avoid evaporation, electric (Calculated aa ethyl alcohol) ETHYLALCOHOL BY: refrigeration requires holding vegetables and fruits in closed Refractive TOTAL containers. Conservation of space is an inducement to pack TREATMENT index 9p.gr. S U Q A R % % % such containers tightly. Under these conditions the gradual Canned immediately 0.05 .. consumption of the oxygen present and the displacement Held in NZ22 hr. at 37O C. 0.79 0:$7 .. by carbon dioxide will in time result in a greater or lesser Canned immediately 0.03 0.01 4.16 degree of anaerobic respiration. Held in NI 22 hr. at 23O C. 0.54 0.56 2.58 Vegetables and fruits are subject to more or less bruising Canned immediately 0.03 0.01 3.76 Held in NI 22 hr. at 23' C 0.49 0.47 2.05 in shipping and distribution. Leaves of spinach are broken and crushed from the necessity for firm packing and from Canned immediately 0.03 0.01 3'.57 Held in N* 22 hr. at 23O C. 0.48 0.49 2.25 handling. Everyone is familiar with the extent to which such fruits as apples and peaches are subject to bruising. The varying nature of the off-flavors developing in different Market vegetables are sprinkled or iced, and, to the extent products is of interest. The off-flavors developing in corn to which they are covered with water, anaerobic conditions under conditions noted in Table I11 may best be described result. This affords an explanation for the inferior flavor as coblike. Such products as spinach, asparagus, and Refu- of a water-laden head of lettuce. The extent to which flavor is gee beans under anaerobic conditions or when frozen in the affected in each instance naturally depends on the nature of raw condition develop characteristically haylike flavors, the product as well as many variable conditions such as time
INDUSTRIAL AND ENGINEERING
776
and temperature and the degree of anaerobic conditions that prevail.
LITERATURE CITED (1) Joslyn, M. A., and Cruess, W. V., Fruit Products
J.,8, 9
(April,
1929).
CHEMISTRY
Vol. 26, No. 7
(2) J o s h , M. A., and Marsh, G. L., Science, 78 (2017), 174 (1933). (3) Kohman, E. F., and Sanborn, N. H., Canner, 74, 64-6, 132-4 (Feb. 2 7 , 1932). (4) Natl. Canners Assoc. 4 n n . Rept., Canner, 65,187 (Feb. 23, 1929); Canning Trade, 51, 124 (Feb. 11, 1929).
K's
(5)
5 * 346 (1933)'
RECBIIVED December 7. 1933.
Pyrolysis Studies Isobutylene, Diisobutylene, Ethylene, Propylene, and 2-Pentene CHARLES D. HURDAND LOUISK. EILERS,Northwestern University, Evanston, Ill. Several olejins are studied at decomposition temperatures in such reaction tubes as quartz, glass, chromium steel (Ascoloy), nickel, iron, and monel metal. Ascoloy is noncatalytic. Euen acetone can be pyrolyzed in it successfully. Nickel is slightly catalytic, iron more so, and monel metal extraordinarily so. The catalysis is evidenced by lower decomposition temperature and the tendency of the reaction towards dehydrogenation and carbonization. The following series of descending stabilities is obtained in Ascoloy: ethylene > propylene, isobutylene > 2-pentene. The liquid products f r o m isobutylene at 700' C. or above contain both unsaturates and aromatics. These are separated by a sulfuric-boric acid reagent.
R
ECESTLY the pyrolysis of isobutylene was studied in this laboratory ( I O ) , but such items as the following were undeveloped: (a)the influence of the size of the reaction tube, (b) the contact time, (c) the polymerization process, (d) the effect of metal tubes or the reactor surface. These and other items are discussed in the present paper.
STUDIESKITH ISOBUTYLEKE CONTACTTIME.' A recent paper on the butanes (9) showed that a t a given temperature the size of the reaction tube was unimportant in determining the nature of the reaction products but that the time of contact of the gas in the hot zone was important. The present study with isobutylene has given a similar conclusion. The experimental methods were the same as for the butanes. For temperature measurements a glass-incased chromelalumel thermocouple, placed within the reaction tube, was used wherever feasible. The temperature was recorded and controlled automatically by a Leeds & Northrup potentiometer-type recorder-controller. With tubes of small bore this procedure was necessarily modified by placing a bare thermocouple within a tube identical t o the reaction tube and touching it. The results (Table I) show that the extent of decomposition and the nature of the products are similar in different tubes if the contact time is comparable, even though the volumes of the tubes may vary fifty fold. A somewhat greater production of paraffin gases is evident in the smaller tube runs, but in general the results reveal similarities, not differences. 1 PT'/FT", where V = tube vol.: 9" = abs. temp. of entering gas; T" = abs. temp. of heated gas: F = av. gas flow rate through tube.
Study of diisobutylene shows that it need not be regarded as a n essential intermediate in the pyrolytic polymerization of isobutylene. Theoretical considerat ions, borne out by experimental data, are offered to show the necessity f o r caution in interpreting the results from the zero conversion method of determining initial products. Compounds which appear to persist at zero conversion m a y be secondary products as well as primary. Experiments o n isobutylene in large and small tubes demonstrate that the extent of decomposition and the nature of the products formed are comparable i f only temperature and time of contact in each are comparable. TABLEI.
c.
P Y R O L Y S I S O F ISOBUTYLENE .4T 700" I N PYREX VARIOUS SIZES AT -4PPROXIMdTELY CONSTANT
GLASSTUBES OF
CONTACT TIME
Size of tube, cc. Contact time see. Rate of flow,'cc./min. Extent of decompn., % Oil formation, % ' by wt. of isobutylene decomposed b
264 12 368 44
77 13 104 47
35
21
15.6 10 26 49
5.45 14.05 6.6 50
40
42
CC. O F G A S E O U S P R O D C C T S PER 1WO CC. OF ISOBUTYLENE D E C O M P O S E D
27 25 27 27 Acetylene 199 181 256 168 Propylene 104 134 84 138 Ethylene 223 271 341 224 Hydrogen 515 456 731 770 Paraffins a The tube sagged during the run, thereby making its volume and contact time somewhat in excess of these values. b Because of the small weight of isobutylene taken, the actual quantity of oils formed in each experiment was small (usually 1 to 2 cc.); experimental difficulty of collecting this liquid without loss is large: t o express the yield as percentage obviously magnifies expermental error.
Experiments were performed a t 700" C. with varying contact times. The extent of decomposition changed gradually from almost 0 per cent a t 0.24 second to 64 per cent in 32 seconds. Seemingly there is a low rate of pyrolysis during the initial stages of the reaction at 700" C. Storch (1'7) observed a similar tardiness in the polymerization of ethylene a t 377" C. Then several experiments were conducted in a quartz tube (volume, 19.7 cc.) with temperature as the variable. A constant contact time of 0.85 to 1.0 second was maintained. Here the decomposition varied from 7 per cent a t 703" C. to 93 a t 862". These results are given in Table 11. It is apparent that the temperature or contact time may be varied independently to produce almost any desired extent of decomposition. This is in keeping with the previously established fact that the extent of decomposition is a matter of
