October 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
by observing the cloud points of binary mistures in the region of 25' C., and estrapolat'ing to 25 C. for the saturation composition at that temperatmure. The completed saturation curves werc represented on ternary coordinates. COXJUGATION LISES. Weighed quantities of the three components lvere placed in t,he apparat,us described and agitated for 2 hours a t 25" C. .It the end of this period the two liquid phase3 were allowed to separate completely at the equilibrium tcmperature over a period of not less than 6 hours. The two phases were sampled into 10-cc. glass-stoppered bottles after separation. These samples, together l+-ith the remainder of the phases, were weighed for a \+-eight balance check on the manipulations involved, and their refractive indes at 23 C.. vas measured. 111 binary and ternary mixturcs of hydrocarbons and solvent vere analyzed by use of the physical property, refractive index. Reference curves of refract,ive indes a t 23" C. against, per cent aniline viere obtained by measuring the refractive indices of binary mixtures at the est'remes of, and of ternary mixt,ures on, the independently determined saturation curves. The accuracy of these curves depends on their gradient, but only in the case of the syst,em aniline-cetane-cyclohcxanewas it found t,hat the gradient was insufficiently steep to be accurate, and this only in the middle portion of the reference curve. Conjugation lines for t,his system were therefore determined at points Corresponding t o the eyindices ll.ere detertremes of the reference curve. mined with an accuracv of one unit in the fourth place bv means of a n Abbe refractometer with thermostatically controlled heated stage and using a sodium D line ~ o u r c eof monochromatic light.
1345
The refractive index data used for rhe various reference curves itre contained in Table 11, together with the dsta for the eat,urat,ion curves. -211unknown ternary niisture was analyzed by measuring it> refractive indes a t 25' C., reading off the percentage aniline f r o a the reference curve, and fixing the concentration of the remaining t x o components by finding the point of intersection with the saturation curve of the h i e corresponding t'o this aniline percentage. By this means one estremity for a conjugation line was fixed When tL7-o extremities of a, conjugat,ion line ha? thus been determined, the acc'm-acy of a line n-as gaged by the colinearity of the extremities and the point representing the rclmposition of the initial misture. With these met,liods phase relation? for t,he following ternary systems were determined a t atmospheric pressure and 23 a C. aniline-cetane-bmzene, aniline-n-heptane-cyclohexane, anilinr cetane-n-heptane, and aniline-cetane-cyclohexane. Equilib rium data for these systems are contained in Table 11. The systems examined include only one system with a single saturation curve-namely, aniline-cetane-benzene: the rrmainder are systems with two saturation rurves. BIBLIOGRAPHY
DaiRTent, B. de B., and m'inkh. (2. A., J. Phw.Chem., 47, 442 (1943).
F,, and Tobias, p, E., IxD. EsGs. CHEM,, 34, 695 ,2, Othmer, (1942). 13) Vartereqsian, K. A., and Fenske. M. R.. Zbid., 28. 929 (1936)
Commerciallv Dehydrated Vegetables J
J
Further Observations on Oxidative Enzymes and Other Factors VI. F. JI=ILLETTE' AND
c. R.
DAAWSOS
Columbia L'nicersity, New York, .V. Y .
W. L. KELSOS
AND W. 4. GORTNER
Cornell University, Zthnca, .V. Y . Evidence is presented to indicate that a relatively high oxidative enzyme activity in dehydrated cabbage does not influence the rate of deterioration of the stored material as measured by color, odor, and ascorbic acid changes. Various blanching techniques show a marked influence on deteriorative changes occurring during storage of dehydrated cabbage. It is indicated that less severe blanching treatments may result in a higher retention of quality.
T
HE first paper in this series ( 7 ) on the osidatire enzymes
and nutritive value of commercially dehydrated cabbage, n-hite potato, and sweet potato indicated that none of the enzymes studied !+-as responsible for t,he storage deterioration of such products. I n addition, no correlation of any of the vitamins (present in these vegetables in nutritionally important, quantities) with the storage deterioration vias observed escept in the case of ascorbic acid. It was also suggested ( 7 ) , on the basis : Present
address, University of W y o m i n g , Laramie, \\-yo.
of ascorbic acid and peroxidase data for two different lots of dehydrated cabbage, as well as a qualitative color and odor record of storage samples, that the blanching process used was important in determining the storage life of the dehydrated product 9 series of cabbage samples blanched by dipping 30 seconds into a hot sulfite solution was found to remain 6,dible longer during storage than a cabbage series blanched 3 minutes with steam: consequently a more evtensive investigation was undertaken of the effect of several oxidative enzymes on the storage life of the dried product. I n order to assure a varied enzyme content, seveial blanching methods were employed. A study of the same oxidative enzymes was considered important, since the earlier work \$as carried o u t on dehydrated vegetables in which these enzymes had all been destroyed (except a little peroxidase in the cabbage) by the blanching and dehydrating procedures. Hence a study of damples containing active enzyme should supplement the previous conclusion that these oxidative enzymeswere not involved in the storage deterioration. Furthermore, ascorhic acid data were
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
1346
TABLEI. A'IOISTURE CONTENT, ASCORBICACID, .4ND ENZYMEDATA O N FRESH, VARIOUSLY BLtlSCHED, AND CORRESPONDING DEHYDRATED C.4BBAGE SAAIPLES
Sample Description Fresh e Blanched Cold sulfitec Hot sulfite Sulfite,steam, 1 min. Sulfite, steam, 4 min. Dehydrated N o blanch Cold sulfite Hot sulfite Sulfite, steam, 1 min. Sulfite, steam, 4 min.
91.4
Ascorbic Acid, 100 &T./ G. Dry Natter 431
92.0 90.5 91.2 91.0
491 304 415 435
3.5 2.2 0.17 0.053
3000 46 0 0
0 0 0 0
5.8 5.7 6.2 9.5 5.6
441 426 265 316 412
3.7 3.7 1.8 1.7 0,001
2900 2900 16 480 0
0 0 0 0 0
Moisture
%'
Enzymeso, Cnits/100 G. Dry Xatter Otherb PeroxiCataoxidase lase dass 3.3 3700 0
Color
Odor 0
c
0
0
..0
0
0
0
0 0
0
0
++ 4+
.. 0
+
0 Size of unit varies from enzyme t o enzyme. Cross comparisons are not valid. b Includes catecholase, cresolase, laccase, ascorbic acid, oxidase, and lipoxidase. N o experimentally significant uantities were observed in any sample. e The fresh and blanche1 samples were delayed during shipment to Columbia University a n d had warmed u p t o loom temperature. The fresh and cold sulfitedipped samples both s h o n e d some darkening probably because of the action of phenolases. This indefinite exposure t o room temperature may account for the failure t o detect any of the oxidases (except catalase and peroxidase) in the fresh and cold sulfite samples.
taken to check again the correlation of loss in this vitamin with the qualitative color and odor indications of storage deterioration. EXPERIMENTAL PROCEDURE
Vol. 39, No. 10
oven method a t 70" C. for 6 hours. Qualitative tests Tvere carried out for peroxidase, catalase, catecholase, cresolase, and laccase, but negative results were recorded for the activities of the last three. Quantitative measurements of peroxidase activity were carried out using a modification of the method of Balls and Hale (Z), based on the rate of disappearance of hydrogen peroxide an followed by titration. Catalase was assayed manometrically by means of the rate of evolution of oxygen from hydrogen peroxide. Manometric methods involving the rate of oxygen absorption by a substrate were used for catecholase ( I ) , cresolase ( I ) , ascorbic acid oxidase ( 5 ) ,laccase ( 4 ) , and liposidase ( 6 ) ,where the respective substrates mere catechol-hydroquinone, p-cresol, ascorbic acid, hydroquinone, and linoleic acid. Lipoxidase was also assayed by s ~ colorimetri~ ~ ~
method (10) in which linoleic acid used 8.S a substrate. Table I includes data taken on samples befo1.e dehydration and immediately after dehydration but before storage. Table 11 contains data 011 dehydrated samples vacuum-packed and stored at 75' * 5 O F., and Table I11 s h o w similar data on samples stored a t 100' * 5 " F. Table I V is a key to the qualitative record of color and odor changes used as an indication of storage deterioration.
DISCUSSION Cabbage n.as chosen for this study since the earlier indications of the importance of the blanching procedure had been The nioisture data indicate a considerable variation i n extent of dehydration, although all five samples were dried under the obtained with this vegetable. A quantity of cabbage as trimmed, cored, and shredded in a regular production line, same conditions and for the same length of time. For some uriandlargeportionswerethen selectedand blanched in various ways. explainable reason, the hot sulfite-treated samples and those The blanching variations included no blanch a t all (dehydration of the fresh vegetable), dipping for 30 seconds in 0.5% sodium bisulfite solution a t room temperature, dipping for 30 seconds in a TABLE11. ~ I O I S T U RCONTEXT, E ASCORBIC ~ C I D ,A N D ESZYMEDATAO N EXPERIMENTALLY BLANCHED DEHYDRATED C.4BR.iQE AFTER STORAQE A'C boiling 0.5y0 solution of sodium bisulfite, dipping 7 5 O * 5°F. in approximately 0,2474 sodium bisulfite solution rlscorbic and then a 1 minute steam blanch, and dipping in Acid, Enzymes", IJniW100 G. D r y )latter approximately 0.24q;b sodium bisulfite solution Rfg./
(cold) then a 4-minute steam blanch. Samples were taken of the fresh unblanched cabbage and of the variously blanched portions before dehydrating, and these samples were quickly frozen in dry ice and forwarded to Columbia University for the enzyme assays. Extracts of similar samples (not frozen) were prepared in the manner described earlier ( 7 ); these extracts were assayed for ascorbic acid a t Cornel1 Lniversity, n-here moisture determinations on all samples were also
jamplt
.\loisture
Description
70'
dtored 13 weeks No blanch Cold sulfite Hot sulfite Sulfite steam, 1 ruin. Sulfite steam, 4 min.
5.2 4.3 6.2 9.4
Stored 21 weeks S o blanch Cold sulfite Hot sulfite Sulfite steam, 1 niin. Sulfitesteam,4min. Stored 27 weeks K O blanch Cold sulfite Hot sulfite Sulfitesteam, 1 min. Sulfitesteam,4min.
5,O
3.8 4 3
5.5 8.1 5.4
100 G. Dry Matter
Peroxidase
Catalase
396 382 216 235 335
3.7 3.7 2.0 1.0 0.003
3600 3800 16 170 0
387 378 212 256 317
Otherb oxi'dase 0 0 0
0 0
Color 0 0
f+ f+
+
Odor 0 0 + t+
4-
..
++ +++ +++
5.6 391 3.0 3900 made. 0 After the blanch the cabbage was dehydrated 5.4 357 2.9 2600 0 $ 7.3 198 0.87 26 0 in a commercial tunnel dryer a t 170" F. for the 7.8 218 0.53 76 0 first, stage and 130" F. for the second stage; 5.4 284 0.002 0 0 samples representing five different predrying treat0 See footnote a, Table I b See footnote b, Table I ments were assayed for ascorbic acid and the several oxidative enzymes. The dehydrated cabbage mas vacuum-packed in S o . 1 tinned cans and placed in storage a t room temperature (75" * blanched with sulfite steam for 1 minute after dehydration were 5 F.) and in warm storage (100 ' * 5 O F.). At suitable storage inteivals moisture, ascorbic acid, and cnzyme determinations badly matted on the trays and contained clumps of moist cabbage. This resulted in samples of variable and high moisture were made, and the color and odor of each sample were recorded qualitatively. content, even after thorough mixing. i n evaluating the storage The methods of assay employed have been previously. considdeterioration, therefore, it mubt be recognized that the relatively high moisture level was possibly the main factor influenczred ( 7 ) and will only be mentioned here. Ascorbic acid was determined in filtered extracts by a modification of the xylene ing the rapid changes that occurred in these samples. Ascorbic acid assays revealed a low vitamin C content for the method (8,9). hloisture was estimated by the 8.0.9.C. vacuum
++ ++ +
~
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1947
1347
the next most nearly normal. The sample that had not been blanched and the one that had bee0 sulfite-steamed for 4 minutes were about equal, being a little less normal because of a bleached appearance; the hot sulfite sample was the worst of all. A rough correlation between the ascorbic acid content and the extent of the abnormal color Odor and odor (scorching reaction) appears in these data. After 13 weeks of storage at 75" F. additional losses in ascorbic acid occurred (Table IT), and +++t some further deterioration in color and odor had taken place, although the enzyme activities were .... relatively the same as before storage. The ap.... parent increase in catalase activity in the unblanched and cold sulfite samples cannot be easily explained but appeared to have no bearing on the storage life of the vegetable. Because no further significant changes in ascorbic acid were recorded after storage for 21 weeks, no enzyme assays were made at that time. After a storage period of 27 weeks a t 7 5 " I?., slight losses of ascorbic acid occurred in most samples, and there were further color and odor changes. Of these samples the cold sulfite-treated cabbage was the best; the unhlanched samples and those sulfitesteamed for 4 minutes \\ere rather good. Comparatively bad were the hot sulfite cabbage and the sample n hich was sulfitesteamed 1 minute. h'o correlation between storage deterioration and enzyme content can be drawn, because t n o of the samples 1%-ith the longest storage life had relatively large quantities of catalase and peroxidase, whereas the third saniple contained vcr. small amounts of the oxidative enzymes. I n some samples there was a reduction of peroxidase and catalase activity. When stored 13 weeks a t 100" F., extensive losses of ascorbic acid and parallel increases in abnormal color and odor were observed. This storage deterioration increased after 27 weeks Some inactivation of perosidaae and catalase also occurred. Tlic cold sulfite sample was changed less by this high tcnipcratui t storage than were the other samples. Although the blanched sample which had been sulfite-steamed for 1 minute was by far the worst, it should be emphasized that the high moisture content may account for its rapid storage deterioration a t this temperature.
TABLE111. MOISTURECONTENT, ASCORBICACID,AND ENZYME DATAO N EXPERIMEXTALLY BLaNCHED DEHYDRATED C.4BBAGE AFTER STORAGE AT 100" * 5 " F.
Sample Descripkon Stored 13 weeks Xi0 blanch Cold sulfite Hot sulfite Sulfite steam. 1 min. Sulfite steam, 4 min. Stored 21 weeks S o blanch Cold sulfite Stored 27 weeks S o blanch Cold sulfite Hot sulfite Sulfite steam, 1 min. Sulfite steam, 4 min. b
Moisture,
%
Ascobic Acid, Mg./ 100 G. Dry Matter
5.3 5.1 6.9
Enzymes", Units/100 G. Dry Matter Otherb PeroxiCata0x1dase lase dase
150 239 81
1.7 2.3 0.82
970 1920 0
0 0
0
9.2
61
0.75
0
0
5.4
143
0.000
0
0
5.8 5.0
96 174
6.4 5.6 9.5
...
...
.. ..
1.9 2.3 0.71
1700 0
0 0 0
Color
+++ ++ +++
++++ +++ .... ....
990
11.9
...
0.34
0
0
6.4
...
0.000
0
0
+++
++ ++++
hot sulfite-blanched sample, n i t h others having a vitamin content approximating that of the fresh sample; the exception was the cold sulfite blanch, which had a high value. After dehydration a marked reduction was observed in the ascorbic acid of the sample sulfite-steamed for 1 minute (Table I), and the vitamin content of the hot sulfited cabbage was still lower. Relatively large and equal quantities of peroxidase were found i n the unblanched and cold sulfite samples both before and after dehydration. I n the hot sulfite sample a smaller but still comparatively large quantity of peroxidase a a s found. Very little could be found in the sample sulfited and steam-blanched for 4 minutes. K i t h cabbage sulfited and steam-blanched for 1 minute, only a little peroxidase could be found after blanching, but a tenfold increase was observed on dehydrating. This apparent increase may possibly be due to enzyme regeneration. The unblanched and cold sulfite samples both contained relat ively large amounts of catalase before and after dehydration. Only a little catalase could be detected in the hot sulfite cabbage, and none could be found in the sample sulfited and steamed 4 minutes. As with peroxidase, a large increase in catalase was observed after dehydration of the sample which had been sulfited and steam-blanched 1 minute. There was no detectably significant amount of other oyidases (catecholase, cresolase, lacease, ascorbic acid oxidase, and lipoxidase) in anv sample. As footnote c, Table I, indicates, unintentional warming of the fresh and blanched samples might explain the absence of certain of these enzymes in the fresh and cold sulfite samples.
TABLE IV. COLORAND ODORKEY Appearance Normal Slight darkening Definite darkening Dark Very d a r k or black
Symbol 0
+ ++ +++ ++++
ODOR--
Predominant Xorrnal Haylike or sweetish , Slightly toasted Toasted Burned
++
+++
+++ ++++
++++ +++ + ++++ +++ +
See footnote a, Table I. See footnote b , Table I.
----COLOR--
++ + +++
Symbol 0
+++ +++ ++++
I n the freshly prepared and blanched cabbage samples there was no evidence of the color or odor characteiistic of the storage deterioration. However, immediately after dehydration significant changes and differences were observed. The cold sulfite sample was easily distinguishable as the most nearly normal in color and odor, and the sample sulfited and steamed 1 minute was
CONCLUSIONS
Certain general observations may be made from the data presented. The type of blanch employed is important to the storage life of dehydrated cabbage. Of the treatments employed, a 30second dip at room temperature in 0.5% sodium bisulfite solution resulted in the longest storage life for the dehydrated vegetable at both 75 and 100" F. Retention of ascorbic acid in this sample was good at 75" F. and better than in any other sample a t 100" F. Cabbage samples dehydrated without any prior blanching treatment and with a $-minute steam blanch were both fairlygood after storage, whereas the hot sulfite and the 1-minute steam blanches led to products that were less stable on storage. The high moisture content of these samples probably influenced the storage stability (3,11). A rough correlation n a s again observed between ascorbic acid content of all cabbage samples and storage deterioration, as evidenced by the qualitative record of color and odor. The extent of deterioration increased with increase in storage time and storage temperature. X o correlation was found between the storage characteristics of the samples and their oxidative enzyme content; this confirmed a previous observation ( 7 ) . It may be that some type of blanching must be employed prior to dehydration to prevent changes in texture and other factors affecting acceptability which were not measured in this experiment. For instance, the untreated controls were
INDUSTRIAL AND ENGINEERING CHEMISTRY
1348
sleached and appeared to be tough in texture. However, these data again indicate the possible adverse effects of uqing a toojevere blanching treatment. ACKNOW LEDGMENT
This study was supported by grants from the Sutrition Pourliation, Inc. Acknowledgment is made to the American Can Company, Continental Can Company, and F. B. H u d e y and Sori "or their cooperation in this invectigation. LITERATURE CITED 11Adams, M. H.,
and r';ehon, J. MI..J . Am. Chem. Sor., 60, 2472'
(1938).
Vol. 39, No. 10
(2) Balls, A. K., and Hale, W.S., J . ASIOC. Ofic. Agr. Chemists, 16,
446 (1933).
(3) Chace, A. M., Proc. Inst. Food Tech., 1942, 70. (4) Gregg, D. C., and Miller, W. H., J . Bm. Chem. SOC.,62, 1374
(1940).
M.,Ibid., 62, 1409 (1940). Jlsllette, M.F , and Dawson, C. R., to be published. 17) Xallette, M. F., Dawson, C. R., Nelson, W.L., and Gortner, IT.A , , ISD. ESG. C H E Y . , 38, 437 (1946). :S) Kelson, IT,L., and Soniers, G. F., ISD.ENG.CHEM.,Ax.4~.ED. 17, 764 (1946). ( 5 ) Stotz, E., J . Lab. C l i .!led., ~ 26, 1642 (1941). (10) Suinner, R. J., IND.ESG. CHEY.,.%SAL. ED.,15, 14 (1943). (11) Tomkins, R. G., Mapson, L. W., Allen, R. J. L., Wager, H. G., and Baker, J., J . Soc. Chem. I n d . , 63,225 (1944). ( 5 , Lovett-Janison, P. L., and Kelson, J. (GJ
Pressure-Volume-Temperature Relations of Benzene EDWARD J. GORNOVI-SKI1, ERWIN H. AMICK, JR2,AND ARTHUR NORMAN HIXSON 1-niversity of Pennsylvania, Philadelphia, Pa. 'rhe vapor pressure of benzene wab determined from 130OC. to the critical point. The critical constants were found to be as follows: Critical temperature 289.5" C., critical
pressure 36,985 mm., and critical %olume 3.36 ml. per gram. The pressure-%olume-temperaturerelations ere determined and the compressibility factors calculated for temperatures ranging from 240" to 355' C. and for pressures ranging from 19,000 to 50,000 mm. It is she-n that the generalized compressibility factor charts for hydrocarbons, which are based on the data for paraffin h>drocarbons, can be safely used for estimating the pre+sure-%olumetemperature relations o f henzene.
I
S T H E past few years considerable infurrnation has been published on the pressure-volume-temperature relations of paraf-
rin hydrocarbons both in the pure state and in mixtures. -4 :lumber of papers dealing with vapor-liquid equilibria in paraffin nydrocarbon mixtures have also appeared. To a lesser extent *:orresponding information on olefinic hydrocarbons and their mixtures with paraffinic hydrocarbons has been presentcd, but r,here is very little published information of this nature on pure aromatics or binary mixtures either in whole or in part aromatic. The measurements presented here represent the initial step iri a proposed program to jtudy the pressure-volume-temperature :elations of aromatic compounds and their mixtures. ;Is the i r s t member of the aromatic series and because of its industrial Importance, benzene was selected for investigation. The most extensive investigations of the properties of benzene vhich are pertinent to this paper have been those of Young (20, cI) on the orthobaric densities of liquid and vapor, the vapor pressure, and the critical constant,s. The data cited in these references have apparently been presented in slightly revised form in a much later paper (19). Vapor pressure data in the range covered in this work have t w n presented also hy Regnault 14), von Huhn ( 6 ) , and Tarasenkov and Afinogenov (17). Other publications (11, 19, 90) are concerned with the critical properties .,f benzene. With the exception of the pressure-volume-temperature data of Young covering the saturated liquid and vapor, and the compres-ibility data of Richards et al. (15, 16) and Bridgman ( 2 ) on liquid : Present address, Standard Oil Development Company, Eliaabetb, N. .I. i
Present address, Columbia University, Kew York, N. Y.
benzene, there have been IIO data published on the P-V-T relations of benzene a t elevated pressure. METHOD AND 4PPARATUS
Xri apparatus of the general type used by Young (19) and Kay ,9), later modified somewhat for operating a t temperatures up to
354" C., was adopted for this work. I t is recognized that other types of apparatus are more suitable for the measurement of P-I--T relations of a pure substance, but this particular equipment was selected because it could also be used for the determination of vapor-liquid equilibria, critical conditions, and P-V-T relations of binary hydrocarbon mixtures. Briefly, the chief components of the equipment employed consisted of a capillary tube in 11-hich the sample of benzene was confined over mercury, apparatus for applying pressure to the mercury, a glass vapor bath in which the capillary and its contents are held a t constant temperature by vapors boiling under a fixed pressure, a pressure regulator system to maintain the desired pressure in the vapor bath, and equipment far dpaerating the benzene simple and loading the capillary tube. The vapor bath of Figure 1 used to maintain the sample in the capillary tube, a t a constant temperature was of the conventional type except for the provision for returning the condensate from the reflux condenser to the boiler by an external by-pass. In its return to the boiler the condensate was passed over a packing of glass, where it contacted in a countercurrent manner the vapors leaving the boiler. This insured against superheated vapors entering the bath. The vapor bath was not only vacuum-jacketed to minimize heat losses but was also provided with an external heater with shielded elements to maintain the outer surface of the vacuum jacket a t a temperature only slightly lower than that of the vapor bbth. The material used in the vapor bath and the temperatures for M hich they were employed are shown in Table I.
TABLE I. Material Acetone Bromobensene Iodobenzene Dowtherm A
hI.4TERIhLS USED IN \'hPOR
Temp., ' C. 50.0 130.0-150.0 160.0-186.0
200.0-250.0
BATH
Material 6-Naphthylethylether Benzophenone Triphenylmethane
Ternp., C. 260.0-270.0 285.0-300.0 310.0-353.9
