July 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
but which react rapidly with organic peroxides. It may be expected that a more reactive compound may be required for best antioxidant efficiency a t low temperatures than for use at high t.emperatures. A number of isolated facts seem to support this assumption. A systematic study of the change in relative stabilizing efficiency with temperature, for various antioxidants, would be of fundamental importance. ACKNOWLEDGMENT
The author is indebted t o C. S. Myers of Bakelite Corporation, under whose direction this work was carried out, for his many helpful suggestions. The assistance given by many of the writer's associates of Bakelite Corporation is also gratefully acknowledged. The experimental procedure was based on information received from R. M. Koppenhoefer of the Socony Vacuum Laboratories. W. S. Gump, of Givaudan-Delawanna, Inc.,
1441
helped the project greatly by supplying many of the compounds evaluated. LITERATURE CITED
Alyea, H. N., and Backstrom, H. L. J., J . Am. C h a . SOC.,51, 90 (1929). Barnett, E. de B., Cook, J. W., and Matthews, M. A . , J . Chem, Soc., 123, 1994 (1923). BGeseken, J., M e t a , C. F., and Pluim, J., Rec. trav. chim., 54,345 (1935). Euler, H.v., ;Idler, E., aud Caspersson, A. O., Chem. Zentr., 1943 11, 20. Fieser, L.F.,J . Am. Chem. Soc., 52, 5204 (1930). Marsh, P. B., and Butler, M.L., IND. ENG.CREM.,38,T O 1 (1946). Moureu, C., and Dufraisse, C., Chem. Revs., 3, 113-62 (1926). Richter, G. H., "Textbook of Organic Chemistry," 2nd ed., p. SOB, New York, John Wiley & Sons, 1943. R E C E I V EApril D 30, 1848.
Sulfite Disap earance in Dehydrated Vegetables during Storage R. R. LEGAULT, CARL E. HENDEL, WILLIAM F. TALBURT, AND LOIS B. R4SMUSSEN Western Regional Research Laboratory, Albany, Calif.
Sulfite disappearance in dehydrated sulfited carrot, white potato, and cabbage stored at temperatures ranging from 24' to 49' C. proceeds approximately as a first-order reaction. The apparent activation energies, calculated according to the Arrhenius equation, are high, ranging from 33 to 43 kg.-cal. The rate increases markedly as the moisture content is raised; for carrot and white potato at 38' C., the increases are about 3- and s-fold, respectively, over the moisture ranges of 5.4 to 8.0, and 5.3 to 9.2%. For sulfited vegetables stored i n air as compared to similar samples stored in nitrogen, the respective rates of sulfite disappearance are in the ratio of about 1 to 1 at 49" C., and 2 to 1 at 24" C. Little change in the sulfite disappearance rate in dehydrated carrot is caused by varying the blanching time from 2 to 8 minutes, by sulfite application during or after blanching, or by application of the sulfite from solution or from gas. On the basis of the generalizations presented herewith, it is feasible to estimate the life expectancy of the sulfite in other samples of dehydrated sulfited \ egetables.
I
T IS generally recognized t h a t the presence of sulfite decreases
t h e rate of discoloration of dehydrated fruits and vegetables, both during dehydration and during storage of the dehydrated product (2-4, 7 , ll).' It is known also that the sulfite disappears fairly rapidly on storage of t h e dehydrated fruit or vegetable a t temperatures above 35" C. and that the rate of disappearance increases as the temperature is raised. Since the rate of discoloration increases after t h e disappearance of the sulfite, knowledge of the rate of sulfite disappearance is of importance t o the dehydration industry. Stadtman and co-workers (9) have reported on the rate of sulfite disappearance in dehydrated apricots during storage, but little information is available for dehydrated vegetables. The principal purpose of this paper is t o report studies of the rate of sulfite disappearance in dehydrated sulfited carrot, white potato, and cBbbage during storage, as a function of the
moisture content, the temperature, and the atmosphere during storage. The results of studies of this rate as a function of the blanching time and the method of sulfite application for one lot of carrot also are reported. These results were obtained in connection with studies of the rate of browning of dehydrated vegetables during storage ( 5 ) . MATERIAL AND METHODS
The commodities studied were dehydrated carrot, white potato, and cabbage. Analytical data on the samples studied and description of the methods of preparation and storage were reported previously ( 5 ) or are included in Tables IV and V. The dehydrated vegetables were packed either in air or in nitrogen containing 1.5 * 0,5'% oxygen and were stored at temperatures ranging from 24" to 49" C. Samples were removed from storage periodically for evaluation. The sulfite content of these samples was determined by the method of Prater, Johnson, Pool, and Mackinney (8). I t is reported as parts of sulfur dioxide per million parts of vegetable on a moisture-free basis (M.F.B.); this is equal t o the parts of sulfur dioxide per million parts of moisture-free solids. Table I records the standard deviation of replicate sulfite determinations on one sample of each commodity after it had been stored at 49' C. until approximately half of the sulfite had been destroyed. I n obtaining these results eight determinations were made on each sample; each of these determinations was carried out on a different day so t h a t day-to-day variation in the personal factor might be taken into account. Replicate determinations on samples of t h e undeteriorated vegetables, reported by Prater et al., show approximately the same degree of reproducibilitj-. Somewhat greater deviations were observed among results for storage samples, presumably because of lack of uniformity among the samples. The moisture content of the dehydrated vegetables Kas determined by the vacuum-oven method of Makower, Chastain, and Nielsen (6). This method \\as used because it gives results
INDUSTRIAL AND ENGINEERING CHEMISTRY
1448
30
E 25
3
I
0 in
6 2 % HPO ( M F B I
0
0
-I
30
25
100
200
100
300
200
Vol. 41, No. 7
and 2). Deviations occur frequently in the direction of the linear (or zero-order) type of relation; such deviations appear to be the rule rather than the exception. Although further investigations of the kinetics of t h s process might be profitable, the deviations from the semilogarithmic relation do not appear t o be of sufficient magnitude t o preclude its use in the estimation of the rate of sulfite disappearance in other samples of these vegetables, as can be seen from data presented later in this paper. The semilogarithmic relation was observed also by Stadtman and eo-workers (9) for the disappearanee of sulfite in dehydrated apricots. The sulfite disappearance data were treated statistically, linear regression lines relating the logarithm of the sulfite content and the storage time being calculated. The slope of such a line, multiplied by 2.303, is the specific reaction rate, 12, in the equation - d (sulfite)/dt = k (sulfite), where the time, t, is expressed in days.
DAYS OF STORAGE
Figure 1.
Approximate First-Order Sature of Sulfite Disappearance
WHITE POTATO AIR PACK
Dehydrated carrot. l o t 1. stored a t 38' C.
I.
DEVIATION, U , O F RESULTS O F SULFITE REFEREWE8.IXPLEs O F DETERIOR %TED DEHYDRATED I'EGCTABLES~
TABLE 8T.4SDARD DETERVINATIONS ON
Commodity
a
SO2 Content, P.P.M. (lF.A l )
u, as %b of 302 Content
P.P.hI. (1I.F.B )
E I
u as
In
T
After destruction of a b o u t half of t h e sulfite.
20
-.
: i 25
which are both more accurate and mole reproducibie (6) than those of the common-hour vacuum-oven method. The latter 100 I 200 100 method was originally developed for dried fruit ( 1 ) and was arbiDAYS O F S T O R A G E trarily adopted for dehydrated vegetables a t the beginning of Figure 2. Approximate First-Order Nature of Sulfite the war. The procedure of LIalton cr et al. gives moisture content Disappearance a t 38' C. values for dehydrated white potato and carrot which are, reDeh,drated white potato, lot 2, at moisture OOntent of 8.0% (M.F.B.) and dehydrated cabbage at moisture content of 3.2% Epectively, about 1.5 and Z%(ofdryn-eightj higherthan the values (M.F.B.) given by the 6-hour method using the sample grinding and sizing procedure described in the Tentative Specifications ( 1 0 ) of the EFFECTOF TEIIPCRATURE. At constant moisture content, a U.S. Army Quartermaster Corps. According t o the latter procedure, the portion of the sample passing through a 20-mesh linear relation is observed when the logarithm of the specific eieve and retained on a 40-mesh sieve is used. The stated differreaction rate, k . is plotted against the reciprocal of the absolute ences, however, represent only rough averages because of lack of temperature, and hence the rate follows the Arrhenius equation precision of the 6-hour method. For dehydrated cabbage, (Figures 3 and 4). Some of the smoothed specific reaction rates are given in Table 11. The change in sulfite disappearance rate approximately the same values are given by the tn-o methods. The stated differences in the moisture content are significant per a 10' C. temperature rise, Ql0, is high (Table 11); the values in the correlation of the data on rate of disappearance of sulfite. obtained range from 5.3 t o 8.9 for a temperature range of 39" t o 49" C. The values are similar for dehydrated carrot and white For example, as will be shown later, dehydrated sulfited white potato stored in nitrogen a t 38' C. shons a difference of about potato but higher for cabbage. The results show that the twofold in the rate of sulfite disappearance b e h e e n samples whose moisture contents are, respectively, 8.0 and 6.5'% h1.F.B. (LIoisture content is also TABLE 11. SULFITE DISAPPEARAKCE IN NITROGEN-PACKED DEHYDRATED reported on a moisture-free basis: the percentage S7hGETABLES AS FuNcrroxs O F TEVPLRATURE AND MOISTURE CONTENT moisture content of a given sample is equal to Initial 100 times the weight loss in vacuum oven per Sulfite Apparent S c tivation HzO Content weight of the oven-dried sample.) R a t e a X 104 Energy, Qie (11F B ) , (If F B ), DETERMINATION OF SULFITE DISAPPEARANCE RATE
The storage data show t h a t sulfite disappearance in the dehydrated vegetables studied can be represented satisfactorily as a first-order reaction-the plot of the logarithm of the eulfite concentration against the storage time being approximately a straight line (Figures 1
% P P.M. 49' C. 38' C. 24' C. 8.0 2190 1100 150 9.3 6.2 1920 810 93 4.8 5.4 1740 580 58 2.5 Carrot, lot 2 6.0 660 810 110 6.5 Cabbage 3.2 930 470 42 1.6 Potato, lot 1 9.2 340 1100 170 14 95 6.5 330 670 7.6 31 340 290 5.3 Potato, lot 2 8.0 400 520 77 516 a Smoothed values from calculated lines (Figures 3, 4, etc.). b Temperature range, 39' t o 49O C. Commodity Carrot, lot 1
Kg.-Cal. 36 39 41 37 43 33 35 40 34
Values 6.2 7.2 8.0 6.4 8.9 5.3
5.9 7.5 5.7
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
July 1949
3.I
3.2
+
3.I
I
I
I
I
3.2
3.3
Figure 3. Effect of Temperature on Specific Reaction Rate of Sulfite Disappearance
I
f x IO'
3.3
x IO'
1449
Figure 4. Effect of Temperature on Specific Reaction Rate of Sulfite Disappearance Nitrogen-packed dehydrated white potato, lot 1
Nitrogen-packed dehydrated carrot, lot 1 t
I
Ql0 value is dependent, in part a t least, on the moisture content of the product, the Qlo values increashg with decreasing moisture content. In correspondence with the high &IO values, the apparent activation energies estimated for sulfite disappearance in dehydrated vegetables are high, ranging from 33 to 43 kg.-cal. (Table 11); the values decrease progressively with increasing moisture content. These values are higher than the value of approximately 26 kg.-cal. found by Stadtman et al. for sulfite disappearance in dehydrated apricots, although this difference may be due to the large difference in moisture content, The values and apparent activation energies for sulfite disappearance are quite similar to those previously reported (6) for the browning reaction in unsulfited dehydrated vegetables, for comparable samples from the same lot of raw material. This similarity suggests that a common rate-determining step controls the processes of browning and of sulfite disappearance, EFFECTOF Mo~sTuRE. The rate of sulfite disappearance increases markedly as the moisture content is raised, over the moisture range covered in these studies. Figure 5 shows plots of the logarithms of smoothed values of k from Figures 3 and 4 against the moisture content. These plots show that the rate approximately doubles with each moisture content increase of 1.5 to 2%. A similar relation was observed for the browning of unsulfited dehydrated vegetables (6). This is additional evidence of the existence of a common rate-determining step for the processes of browning and of sulfite disappearance. EFFECTOF OXYGEN.The effect of oxygen on the sulfite disappearance rate is largely dependent on the temperature. At 49' C. the oxygen effect is scarcely measurable, as is shown by the fact that the rates observed at this temperature for nitrogen-packed and air-packed samples are nearly identical
TABLE 111. SPECIFICREACTION RATESIN DEHYDRATED VEGETABLES PACKED IN NITROGEN AND IN AIR
Commodity White potato, l o t 2 Carrot, l o t 1
HzO (M.F.B.). % 8.0 8.0
8.0 0.2 6.2 6.2
Initial Sulfite Content
(M.F.B.), P.P.M. 400 400 400 1920 1920 1920
Storage
Tynz., 49 38 24 49 38 24
Smoothed d a t a from calculated lines (Figure 3, etc.).
R a t e a X lo4 Nt Air pack pack
Figure 5.
I
POTATO
WHITE
t
I
I
I
6.0
7.0
,
I
1
,
CARROT
I
8.0 9.0 6.0 PERCENT MOISTURE (M.F.B.)
70
8.1
Effect of Moisture Content on Specific Reaction Rate of Sulfite Disappearance
Nitrogen-packed dehydrated carrot, l o t 1, and white potato, lot 1, using smoothed values from calculated lines, Figures 3 and 4
(Table 111). However, as the storage temperature is lowered, the effect of the oxygen becomes progressively greater over the temperature range studied, the rates observed a t 24' C. for the nitrogen- and air-packed samples differing by about twofold. ( I n these experiments, no more than 25y0 of the oxygen initially present in the atmosphere was consumed during storage of the white potato samples and no more than 60% during storage of the garrot samples.) The fact that disappearance proceeds faster a t 24' C. in airpacked samples than in the nitrogen-packed samples indicates that there are a t least two processes by which sulfite is destroyed; oxygen of the container atmosphere plays a part in one of these but not in the other. The fact that sulfite disappearance does not proceed faster a t 49 O C. in the air-packed samples than in the nitrogen-packed samples indicates that the process that involves oxygen has a considerably lower temperature coefficient than the other.
520
530 120 14 810 900 93 130 4.8 8.5
77
5.6
ESTIMATION OF SULFITE DISAPPEARANCE RATE IN OTHER SAMPLES
The generalizations and data presented above can be used t o estimate the life of the sulfite in other samples of dehydrated sulfited vegetables a t various moisture levels and a t various
Vol. 41, No. P
INDUSTRIAL AND ENGINEERING CHEMISTRY
1450
excessive leaching losses of substances reactive toward sulfite under the conditions prevailing during storage. CONCLUSIONS
Sulfite disappearance in dehydrated sulfited cabbage, carrot, and white potato stored at temperatures ranging from 24" to 49' C., proceeds approximately as a first-order reaction. The specific reaction rate follows the Arrhenius equation over the temperature range studied. The apparent activation energies are high, 003 ranging from 33 to 500 43 kg.-cal., depending on the vegetable and the moisture content. The sulfite disappearance rates increase m a r k d l y with increasing moisture content over the range studied, increasing approximately twofold with each moisture con--_ I tent increase of 1.5 to 2% for dehydrated sulfited carrot and white potato. The effect of oxygen on the sulfite disappearance rate is
w
LL
-1
I00
LL 1
u
r
5O
20
L
IO
I
5
6
I
7
1 8
PERCENT MOISTURE ( M F B )
Figure 6. Effect of Moisture Content on Half Life of Sulfite in Nitrogen-Packed Dehydrated Carrot, 1,ot 1 Smoothed values from calculated lines. Figure 3
I
L
storage temperatures by means of plots such as Figures 6 and 7 . The degree of accuracy of half-life values predicted for other lots of dehydrated sulfited carrot is indicated in Table IV. The estimated and observed values for these five lots of carrot are in reasonably good agreement. Further, the differences between the observed and estimated half-life values of Table IV are for the most part consistmt with the representation of the sulfite disappearance as a first-order reaction, deviating in the direction of zero-order, For example, in TABLEIT.'. COMPARISOX OF SULFITEHALFLIFE ESTIVITIGD FROM lot 2, for which the largest percentage difference FIGURE 6 WlTH O B S ~ R V EHALF D LIFE occurs, the observed half life is 54 days, and (Dehydrated carrotU stored in nitrogen at 38" C.) the estimated half life is 82 days. In this Initial lot, the sulfite content was 660 p.p.m. (M.F.B.) Sugar. % Sulfite H20 Half Life, Days (aI.F.B.1, (M.F.B.). (M.F.B.). m-hereas the sulfite content was 1920 p.p.m. Lot Variety Reducing Total P.P.X % Estimated Observed (3I.F.B.) in the lot-1 carrot at about the same b 6.0 82 54 2 8.0 49.3 660 3 23.8 51.6 650 7.5 61 b 34 moisture content. (The sulfite disappearance 74 4 Red Core , . 51.2 2330 6.2 63 rates of lot 1 were used as the basis for these Chantenay 7.0 65 54 3 Imperntor 22.3 55.7 1700 estimations.) If the sulfite disappearance fol63 22.6 54.9 2330 6.9 59 5.4 120 84 2 3 . 4 5 7 . 3 1250 lowed a zero-order relation, the half life would 22.7 54.9 1050 5.3 128 112 6 ChRntrnay 31.8 01.5 900 6.4 68 49 be directly proportional to the initial sulfite 34.8 53.2 1400 6.4 A8 49 content. Hence a value of 82 X 660/1920, Half dice measuring 0.375 X 0.378 X 0.1875 inch before dehydration, except, lot 2, or 28 days, would be estimated as the sulfite which was full dice, 0.375-inch cube, before dehydration. b Commercial samples of unknown variety. half life if the process nere assumed to be zero-order. I n accord with this example, the data of Table I V show that the observed halfTABLI? I-. EFFECTO F PRoCESsING CONDITIONS O N Rarr, O l p SIJLAITE life values are for the most part intermediate DISAPPEARANCE between values estimated for first-order and for (Dehydrated Red Core Chantenay carrot stored in nitrogen a t 38' C.") Specific Reaction zero-order reactions. Initial RateC X 10' EFFECT OF PROCESSING CONDITIONS
The effect of varying certain of the processing conditions on the rate of sulfite disappearance is indicated in Table V. No significant effect was caused by varying the blanching time from 2 t o 8 minutes, by sulfite application during or after blanching, or by sulfite application by spray or as gas. However, a 90-minute soak after blanching reduced the rate t o about 6% of that for comparable samples which were not soaked. This radical reduction in rate is presumably the result of
Processingh
Total Sugar (M.F.B.),
%
52 .0 50.3
48.9 03.0 51.2
B2 B8J
B8 SO2 gas D B B4: 90-minute soak after blanch, followed b y sulfite
-
55.2 21.9
Sulfite Content
(R.Z.F.B.), P.P.M.
Ha0
(M.F.B.1, %
Obserled
Corrected to6 2
HzOP
6.4 6.1 6.3 6.2 6.2 6.0 6.3 5.7
5 Half dice measuring 0.375 x 0.375 X 0.1875 inch before dehydration. b B2, B4, B8 blanched in steam 2, 4, and 8 minutes, respectively: Dl3 blanch; AB = after blanch. 0 Reciprocal days. J From Figure 5 .
-
during
July 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
negligible at 49 C. but increases with decreasing temperature. At 24’ C. the rate of sulfite disappearance in air is approximately twice the rate for corresponding samples in nitrogen. Little change in the sulfite disappearance rate in dehydrated carrot is caused by varying the blanching time from 2 t o 8 minutes, by sulfite application during or after blanching, or by sulfite application by spray or as gas. However, a marked d e crease in the sulfite disappearance rate is caused by prolonged soaking in water before dehydration. On the basis of the generalizations presented, it is feasible to estimate the life expectancy of the sulfite in other samples of dehydrated sulfited vegetables. ACKNOWLEDGMENT
The authors wish to acknowledge the interest and helpful suggestions of J. R. Matchett, under whose guidance this work was performed. Appreciation is expressed also for the cooperation of C. G. Seegmiller, B. Makower, M. F. Pool, L. R. Leinbach, Louise A. Bryan, and D. C. Patterson.
1451
LITERATURE CITED
Assoc. Official Agr. Chem., “Official and Tentative Methods of Analysis,” 5th ed., p. 336 (1940). Burton, W.G., J.Soc. Chem. Xnd. (London),64,215-18(1945). Cruess, W. V., and Mackinney, G., Univ. Calif. Agr. E x p t . Sta. Bull., 680 (1943).
Gore, H. C., and Mangels, C. E., IND.ENG.CHEM.,13, 5235 (1921).
Legault, R. R.,Talburt, W. F., Mylne, A. M., and Bryan, L. A , Zbid., 39,1294-9 (1947). Makower, B., Chastain, S. M., and Nielaen, E., Zbid., 38, 725-31 (1946).
Mangels, C.E.,and Gore, H. C., Zbid., 13,525-6 (1921). Prater, A. N., Johnson, C. M., Pool, M. F., and Mackinney, G., IND. ENG.CHEM.,ANAL.ED., 16,153-7 (1944). Stadtman, E. R., Barker, H. A., Haas, V., and Mrak, E. M., IND. ENG.CHEM.,38, 541-3 (1946). U. S. Army Quartermaster Corps Tentative Specifications CQD No. 58C, 598,and 73D (1945). U. S. Dept. Agr., iMisc. Pub. 540 (1943). RECEIVED February 24, 1948.
Fermentation of Bassia Flowers B. A. MANDE, A. A. ANDREASEN, RI. SREENIVASAYA, AND PAUL I
