Commerciallv Dehvdrated Vegetables J
J
Oxidative Enzymes, Vitamin Content, and Other Factors M. F. MALLETTE AND C. R. DAWSON Columbia University, New York,
N. Y.
W. L. NELSON AND W. A. GORTNER Cornell University, Ithaca, N. Y. Commercially dehydrated cabbage, Irish potatoes, and sweet potatoes were stored for one year under controlled conditions of temperature, moisture, and atmosphere. The fresh, blanched, and dehydrated samples were assayed for vitamin, oxidative enzyme, available iron, total copper, and moisture content. Similar analyses on the dehydrated samples were made several times during the storage period. The dehydrated cabbage and potato deteriorated rapidly as evidenced by loss of ascorbic acid, discoloration, and development of off-odor when stored above 70-80' F. and a t moisture levels above 7% in the case of the white Rotato. A t lower storage temperatures the products were more stable. No correlation between this
deterioration and the oxidative enzyme content or iron and copper content of the dehydrated vegetables was found. All the vitamins assayed except ascorbic acid were fairl? stable during storage. The use of sulfite in the blancb reduced the ascorbic acid losses in dehydrated cabbage during storage. However, thiamine was destroyed by the sulfite. There was no evidence of any significant amounl of oxidative enzyme regeneration during the storage period. The data do not support the view that the storage deterioration of commercially dehydrated cabbage and potatoes may be due to the action of oxidative enzymes whose presence might arise from inadequate blanching or regeneration during storage.
D
fresh product we8 found t o be highly unsatisfactory for protecting against vitamin losses during transportation from the manufacturing plant to the laboratory a t Cornel1 University, where the vitamin assays were made. As a result, extracts of all fresh and blanched materials were prepared for vitamin analyses a t tbe plant.
URING the past three or four years large quantities of dehydrated vegetables have been produced for the armed forces and for Lend-Lease distribution. In many cases these products deteriorated rapidly under the prevailing transport and storage conditions. There has beeh a marked tendency to attribute the deterioration to enzymatic activity remaining in'the product after processing or t o regeneration of the activity during the period of storage (2, 4, 6). This view was reflected in t h e fact that the army specifications for dehydrated vegetables called for a negative test for certain oxidative enzymes-Le., peroxidase and catalase. However, little or no data are available which show a correlation between the deterioration of a dehydrated vegetable and the presence of a specific enzyme system. Because of the suspected oxidative nature of the changes observed in dehydrated vegetables, it was decided to investigate several oxidative enzyme systems rather than just peroxidase and catalase. Deterioration in dehydrated vegetables is evidenced in several1 ways-e.g., a change in color, odor, taste, and vitamin content. Of these factors, vitamin content was chosen as a measure of deterioration because of its importance and capability of accurate measurement. I n general, only the vitamins present in nutritionally important quantities in the raw vegetable were investigated. The specific objectives of this joint investigation were, therefore, to aetermine if a correlation existed between enzyme content and nutritional deterioration, discoloration, and off-odor development observed during storage, and t o investigate the possibility of enzyme regeneration during the storage period. Samples were collected during actual commercial production at various dehydrating plants. The fresh and blanched Laterial was collected in friction-top lacquered cans, and quick-frozen by means of dry ice. The dehydrated product was collected in the containers used in commercial production. Cabbage was packed under nitrogen gas. Duplicate samples of each collection were packed in dry ice a t the plant and immediately shipped t o Columbia University for enzyme studies. Quick freezing of the
VITAMIN DETERMINATIONS
REDUCEDASCORBIC ACID. Suspensions of the fresh and blanched vegetables were prepared at the plant by blending with 6% metaphosphoric acid solution in a Waring Blendor These suspensions could be transported t o the laboratory for analysis as the ascorbic acid content was found to be stable for several days. Suitable aliquots of this mixture were diluted witb water t o make a 3% metaphosphoric acid concentration and fil. tered. In the case of the dehydrated product, it was first ground through a 20-mesh screen in a micro Wiley mill, extracted witb 3% metaphosphoric acid, and filtered. The reduced ascorbic acid concentration of the filtered extracts was measured by e modified xylene method (17, 22). RIBOFLAVIN, NIACIN, AND THIAMINE.Suspensions Of the fresh and blanched vegetables were prepared a t the processing plant by blending with 0.5 N hydrochloric acid in a Waring Blendor. The suspensions were transported to the laborator? and, the following day, were autoclaved for 15 minutes a t 15 pounds pressure. The cooled mixtures were adjusted t o pH 4.04.5 with sodium hydroxide; 4 ml. of a suspension containing 160 mg. each of takadiastase and papain were added, and the mixture was incubated for 12 hours a t 37" C. The mixtures were filtered and made to volume, and aliquots taken for vitamin analyses. In the case of riboflavin and niacin the extracts were adjusted t o a pH of 6.6-6.8. Riboflavin was determined by the microbiological method of Snell and Strong (20). Niacin was determined by the method of Snell and Wright @ I ) , as modified by Krehl et al. (IS). Thi437
438
INDUSTRIAL AND ENGINEERING CHEMISTRY
Domestic Sone None Shredded
AIixeil None Kone Shredded
White Potato Ilatahdin Cellar Contour steam Diced
30 see.
Hot SO? dip"
Swam 3 inin
?tea,m 3 min.
Steam 5 niin.
Cabinet
Zuii~iel
Tunnel 6c
Tunncl 6.5
170 130
210 150
240 165
Cabbage I t.\
Btorage Peeling Form of
'
clif
Blanching Tvpe Time Drying Type Time, Iir, Temp., 1' Initia! Finishins Final mokiun:,
%
Cabbsix 2
5b
.
...
.
,
.
Puerto Riran Sheds Camtic Diced
3.15
7.19d S .57 Air .iir t o boiling temperature. b Conditioned in fiber d r u m for ahoul 1 week, then redriod t o tinal oioist u r e in cabinet dryer. Plus 24-48 hours in bin a t 105" li'. i n t h e case of t h e p o t a t o samplo Kith 7.197? moisture. d 13.02% moisture after B-hour tunnel drsing.
Pack
'I 08
,
Swcet r'otato
CO?
coz
a 0.5% s o d i u m sulfite solution heated
amine ivas dotermined as the hydroc~hlorideby the tliiochronii, method ( I ] ) . CAROTENLThe determination as carried out cisxitially as outlined by Moore (16). However, it \vas round necessary to rehydratc the ground sweet potatoes with natcr before extracting with alcohol j the ratio of water t o ground dehydratcd material was 4 t o 1. Extracting the original material with 03$o alcohol gave only about half the carotene value obtained when tho material v a s first rchydrated with water. E\I%Y.ME A S S A Y
PIIEPAKATIOS OB' E ~ T ~ I A W S . Cabbage samples Ivere handground in a mortar with n t e r , pH 7.0 citrate-phosphate buffer (McIlvaine), and Berkshire sand. The mixture was then centrifuged, and the extract decanted and used immediately for enzyme assay. Khitc potat'o and sweet potato extra& ~ v c r c prepa,red in Rlcllvaine buffer (pH 7.0) with a Waring Blendor since tlic dehydrated pot,atocs were extremely difficult to grind by hand. Thcy n'cre centrifuged and used immeciiat cly Cor onzyme, assay. Ho\mver, it \vas juclgcd iii;idvisabIe t o grind c a l ~ bagc w i t h the Blendor because t h c violmt intcrmisiiip o i air it]activated most of the ascorbic acid oxidase. T o est,imiitr the rcproducibility of thc extraction pro , in additiou to the qiimtic cxtrnct KRS dialyzcd atid tative activity \~alucs,an aliquot o the undialyzable solids ~ c r dctcrmincrl e by ctvnpor:it iiin t o dryness at 80" C. Q,CAL~'L'ATIVF, Twrs. Test,- ~ c r made e For pcrusitl lase, catecholase, cresolaw, and laccase activity prio complete enzyme assay, which inoliided also nscorbic acid osid and lipoxidase. These qualitative tests in most ciiscb w r c c:tpable of detccting smaller amounts of crixyme activit,y t1i:in could be assayrtl quant,itatively. 9m:Lll specimeiis oC tlic f blanched, or rehydrated vcgetable were p1:tced in systems c o l i sist.ing of about 10 ml. of Tratcr, 1 ml. of McTlvainc pH 7.0 buffer, and 1mi. of a 1%solution of the prtrticular substrate i t i qucstion. For peroxidase the substrates were benzidine, guaiacol, :md cat(,chol in the preeence of about 0.01 A- hydrogcn pcrosidc. For catecholase, eresolase, a,nd lnccasc the substrates 'rvcre catechol, p-cresol, and hydroquinone, respectivcly. Thc detection of cat,a.lase was based on the evolution of bubbles of oxygen from tho surface of the sample suspended in about 0.01 N hydrogcii pcroxide. With the exception of catalase, the presence of enzyme was detccted by the development of colored reaction products at room temperature. Because of the susceptibility of the suhstrates t o slow aerobic oxidation, colors appearing on the vegetable sample after standing for an hour u'ere not considered positive tests. QUANTITATIVE TESTS.Peroxidase activity was estimated by a rnodificat,ion, of the method of Balls and Hale ( 3 ) . A reaction
Voi. 38. No. 4
volume of 55 ml. \\-as employed a t 25 C. with atmosph excluded by means of a continuous stream of nitrogen through the system, as used by Balls and Hale, but without t'he minei'al oil r c layer. Aliquots for titration ol hydrogen peroxide ~ ~ riithdrawn at varying intervals by a pipet which WSLSfillcd by prcssm' of nitrogen on the surface of the roaction mixture. Catalase was assayed manometrically by f o l l o ~ i ~ tho i g rate of evolution of oxygen from hydrogen peroside at 2.5' C.and pFI 7.0, in a volume of 8.0 rml. The less sensitive titrimetric method of von Euler and Josephson ( 8 )~ 3 employed s in a supplerncntary manner where rclatively large amounts of the enzyme ~vere found. Ascorbic acid oxidase :tctivit'y LP'U irriated by tile triarlometric method described by Lovett-J son antf Sclson (24) ; the usc of gelatin was found to be unni:ccss:try with t.he c:rude cst'racts. Laccase \vas det'criniried by the manometric mcthod of Gregg and Miller (A), arid the cresolnsc activiity of tyrosinase w;is assayed by the maiiomctric mctllod of Gregg a,nd Selson ( 1 0 ) . The catecholase activity of tyrosina3c wa.s cstimatcti according t o the manometric method of rZdams a ~ r dYelson ( I ) . Although there are fundamental objcctions to t,he I:tt.tcr ( 1 5 ) :M applied to purified tyrosinase, it is particularly suited to crudrl L. 'Ytr2Lcts containing small amourit8sof eimyinc. Jiposidaee assays xrere madc by Sumncr's colorimetric method (Cs), employing linoleic acid as substrate. Serious difiiculty LIXB encountorcd in the turbidity of the fincil solutions, prtrtic~ilnrly vith est'racts from dehydrated potatocis. This lrd t o t h o rlcvclopment of a manometric method based on tlir oxygen absorbed during the enzymatic oxidation of linolcic acid. D c t a i l ~ of this manometric method n-ill be published 1. All enzyme assays were corrected for nonenzymatic catalysis by comparison with "boiled" controls. 111 no casr: n-as there significant ~inncnnymntica r t i o i i i t 1 ~~)iitroI~. 1 1 i c 3
(-oLoi?
Appearance Sormal Slight darkening Definite darkenin:! Dark I-ery dark or black
OUoR
Symliol
-/ I i- + +-+it + i- +
I'redoininimt Sormal Haylike or swcctibh 'roasted tonstecl Slightly JSurned
3.mbol
+0
t$
,-T++
'Lhc osidativc erizyme contonts in tlic tables for the various vcgetable samples arc espressed in units ~ i cnzyrnc ' activity. ' h e activity units a r c iu each case proportional to the rate of the n-ith spvific substrates. In the uiiit is h a r d 011 the first-ordcr rate -caialyzed reaction bctn.ccti pyrogallol and hydrogen Fur all of t h e manometric methods employed, the uuit o f d i v i t y corresponds to t list amount of enzymes causing a rate of reaction of 10 cu. mm. of osygcii per minute. Bec:ause of the diffclent cnsymt~-~ubstr:ii (' systems and reactions involved, the use 01 10 rii. mm. of osygr:ii pcr mi a n equivalent amount of enzy ticularly emphasized that t h c metric: liposidasc, zinc1 the various .c: cross comparisons, tivitics diffcr by l a r g Eactors in re1 therofore, geircrdly c:innot be made. ,411 onzyme activitics in tlie tables are csprerscd as uiiits pcr 100 gi':iins of s:implc~calc~ul:itrcito a dry basis. IRON,
comm, AND
MOISI'URE
Chemically available iron 1% as determincd by the dipyiidyl method of Hill (22) as modified by Elvehjem et al. (i), Shiickelton and McCance (19), and Thierault and Fellcrs (y). l n coniicction with the analytical mcthod? for iron, one of the greatest
INDUSTRIAL A N D ENGINEERING CHEMISTRY
April, 1946
sources of error was found to be in opening the cans. Most conventional can openers caused a flaking off of small particles of metal from the can which contaminated the contents. No single opener was found t o be entirely satisfactory. The most successful for cans containing solid material is an opener that cuts a circular line along the side instead of from the top. I n this manner the particles sheared from the can tend t o fall outside instead of into the contents. This point should always be given consideration when mineral analyses are t o be run on material stored in sealed cans. The colorimetric diethyl dithiocarbamate method of Parks et al. (28)was used t o estimate copper, after incorporating a number of modifications suggested by Ellis (6),including a dry ash at temperatures not exceeding 400' C. in the presence of magnesium oitrate. Because of the minute amounts of copper present and the experimental error involved in the t o t 4 copper measurement, it did not seem advisable t o attempt t o differentiate total copper from so-called available copper. Moisture was determined by the vacuum oven method of the Association of Official Agricultural Chemists, at a temperature of 70" C. and a time of 6 hours. CABBAGE
processing data obtained during the dehydration of the various vegetables are given in Table I. Table I1 is a key t o the color and odor record. The two series of cabbage samples were processed at different times; after collection both were stored at Cornel1 University in No. 1 cans under an atmosphere of carbon dioxide at various temperatures. These two cabbage series differed not only in the mcthods of blaiiching and dehydrating but also in the final moisture level of the dried product (Table I). The significance of the difference in variety cannot be evaluated from the data at hand. fudging from the time of blanch and the moisture level of the dried product, cabbage series 2 might be expected t o show the 'llit*
439
longer storage life if the deterioration during storage were largely due t o enzymatic processes. It must be kept in mind that, at the time these studies were initiated, such enzymatic processes were thought t o play a prominent part in the storage deterioration of dehydrated vegetables. However, cabbage 1 proved t o have a longer storage life than cabbage 2. This conclusion is based on a comparison of the rates of deterioration of the two series as shown by the ascorbic acid data and color and odor record of Table 111. The enzyme data in Table I11 reveal that significant amounts of peroxidase, catalase, and tyrosinase (catecholase and cresolase) were initially present in both series; but after blmching, dehydration, and storage, only peroxidase remained in both series in measurably significant quantity. Values of less than 10 units of activity per 100 grams of dry matter are not experimentally significant in the cases of catalase, ascorbic acid oxidase, catecholase, cresolase, and laccase, all of which were measured manometrically. 'These data, coupled with the fact that the amounts of peroxidase present in the stored samples of both series were approximately equal, makes it clear that the noticeable type of storage deterioration in cabbage series 2 is not due primarily t o oxidative enzymatic action. If one assumes that peroxidase action is the fundamental cause of deterioration, then the storage life of both cabbage series should have been about the same. As a result of studies in numerous laboratories on the effect of gases in storage containers, an important role in the deterioration of dehydrated vegetables during storage has been ascribed to oxygen. For this reason it seemed possible that catalytic oxidations induced by metallic ions might be important, consequently chemically available iron and total copper contents were investigated. However, the available iron data were approximately the same in both cabbage series (Table 111) and thus the longer storage life of cabbage 1 cannot be explained in terms of the iron content. Cabbage series 1, having the longcr storage life, contained considerably more copper than did cabbage 2.
TABLE 111. ANALYTICALDATAON FRESH AND COMIUERCIALLY DEHYDRATED CABBAGE Available Iron, Uescriptioo of
Sample
Fravh Blanched Dehydrated Dehydratedd Stored 70-80' F. 6 weeks 15 weeks 23 weeks 27 weeks $tored 95-105" F 6 weeks 15 weeks 23 weeks
hIg./100 G. Dry
Matter
Ribo-' tlavin
Thiamine
92.41 94.29 3.42 4.08
io: 6
0.50 0.32 0.41 0.40
Sulfite-Blanched Cabbage, Series l b 3.09 6.6 250 0.33 2.43 345 50 0.05 3130 250 6:O 13 0.12 3.23 307 4.1 LO
4.34 4.20 4.68 5.26
7.3 8.0 7.8
4.94 4.80 5,58
7.7 8.0 7.8
XI&ture, % '
7.1 7.6
..
0.41
0.40
.. I
.
0.39 0.41
..
Niaoin
bic acid
Peroxidase
Catalese
,
0.W
0.07 0.04
.. ..
0.04 0.03
..
2.92 2.71
.. ..
2.79 2.66
..
acid oxidase 43 0
0 0
275 291 282 255
0.05 0.02 0.02 0.02
0 6 0
0 0 0 2
238 122 40
0.02 0.02 0.02
0
0 0 0
0 0 2
Cata- ' Cresocholase lase 190
70 5 13
0
0 2 0 5
0 0
100
0 0
0
20 4 7
0 0
0 0 0
0 6
0 0
4-
0
0 0
0 2 0
0 2
5
0
Steam-Blanched Cabbage, Series 28 0.74 4.43 477 6.4 18,000 0.63 4.20 380 0.02 50 0.55 3.86 266 0.02 0
0
+ ++ ++ ++ ++++
++$ ++ ++ +++
$reah 92.30 13.0 0.61 0 80 50 40 0 0 Blanched 93.00 0.48 5.8 0 40 50 30 0 5.2 0.45 Dehydrated 3.15 20 0 9 20 Stored 40-50' E. 9 weeks 3.83 8.3 0.44 0.70 3.53 228 '0.02 0 0 2 0 2 0 3.60 0.3 17 weeks .. 0 0 0 0 0 4.14 21 weeks 8.8 .. 0 0 0 0 0 t 3.35 9.7 28 weeks ,. ... 10.2 3.69 46 weeks .. 0 2 2 0 3Stored 70-80' E. 3.48 10.7 0.41 9 weeks 0.66 3.73 235 0.02 0 0 7 0 0 t+ 3.94 7.8 17 weeks .. .. 223 0.03 0 0 2 2 0 4.53 7.2 21 weeks ,. .. 228 0.03 0 0 0 0 0 28 wee& , 3.88 7.0 .. .. .. 182 .. ... ... .. 4.10 46 week .. 8.0 205 0:Ol 0 0 2 0 0 stored 95-105' E. 9 weeks 3.79 11.6 0.46 0.69 8.67 131 0.02 0 0 0 0 0 4.53 17 weeks 8.3 50 0.01 0 0 0 2 0 t+++ * Lipoxidase also determined on all sam lea values on the fresh material were 80 low a8 to be oonsidered insignificant. Size of unit varies from ensyme cu enzyme, cross comparisons are not valid! 6 Total coppar was also determined. values for all samplea were of the order of 1 mg./100 grama dry matter. 0 Sample was quiok-frozen at plant 'and had an ascorbic acid value of only 59 m ./lo0 grama dry rnatt;er when analyzed 18 hours later. f Sample taken from stora e at plant, and studies continued on this sample. (*able I footnoteb.) Total copper values €or a%aampl6a were of the order of 0.3 mg./100 grama dry matt&.
..
I
..
..
..
'
.. .. .. ..
.. ..
...
..
..
++ ++
+++ +++ ++++ ++++
+ ++ +
++ ++
+++
+++
'
INDUSTRIAL A N D ENGINEERING CHEMISTRY
440
TABLEIT'. Orscriutioti of .. 8a;irplr
.%Y.\LY'II(7.41~
SIoisture.
%
D.iT.4
ON E'RESH d S D ~ O X M E I Z C I A L L Y DEHYDRATED IRISH PoTa4ToES
Mg./l00 G. Dry Matter --__ Availahle A s c o r b i c ironR acid Peroxidase
V O ~ . 38, WC.
(STEA\I-BLA~-CIIEU)
Enzymes, Unitu/100 Grams of Dry M a t t e r b Ascorbic-. Catalase
iriri
_"__
oxidase
Cat@-
cholase
Cresolase Laccase 850 47 2 0 2 2
Physical
Lipoxidase 6300 0
2
1:.
...
Thus as with iron, the deterioration during storage probably ('311not be ascribed to the action of copper. Although there was a slight decrease in the riboflavin content ,)i cabbagc during the processing, there was no further loss in the iried product during storage up t o about 4 months, even at 95L 0 5 O F. In the steam-blanched cabbage 2 there was likewise no iignificant loss of thiamine during storage, Hoxvever, the use if sulfite during the blanching of cabbage in series -1 almost comJletelg destroyed thiamine. Although there appears t o be a 'c>ndencytoiyard loss of niacin in dehydrated cabbage during +torage, the data offer no evidence that this trend is associ3ttd Srith storage temperature. Of most interest are the ascorbic acid data, which were U S C a~ i itn index of the rate of deterioration. As a matter of fact, tiir Ascorbic acid content rsas the only nutritive, enzymatic, or metal.ic fact,or measured xhich correlated with storage dcterioration i s qualitatively indicated by the record of abnormal color and )dor development. The effect of temperature on storage dcrerioration is clearly shown by the vitamin C data for both cab5age series; the higher the storage temperature, the more rapid r,he loss of ascorbic acid. However, in the sulfite-blanchpd cahSage the loss in ascorbic acid and the development of abnormal ,:olor and odor n'ere less pronounced during storage at 95-105' F. :han in cabbage 2, receiving a more drastic blanch. In series 2 itlmost 50% of the ascorbic acid content of the cabbage was lost ,iuring t,he blanch and dehydration process, but on storage a t low :emperature (40-50 F.) the vitamin C conbent' remained cond a n t for nearly a year. WHITE POTATO
Table I17 contains data on the storage of commercially dchy'irated Irish potatoes. They had been in cool storage for about 5 rnont,hs prior to dehydration. They were steam-blanched for 5 minutes and dehydrat,ed to tTvo different moisture levels, sbout 7 and 13y0. One lot of potatoes, which IWS not stored, was dehydrated to 20.7%. The fresh vegetable contained experimentally significant amounts of all enzymes, with the possible exception of ascorbic acid oxidase. After the 5-minute st'eam blanch, none of the enzymes (not even peroxidase) could be detected by qualitative tests. Of the quantitative onzyme data in Table IP,only those
. .Characteristics ~
~
Color 0
il
0 0
0
3
(1 V
0
Odor 0 II
0 0
1
2 1
3
Q
I
0
I
0
0
n
i
0
3
0
7
0
(I
B , stored 40-50" F.
13.1 2.8 19 6 weeks 0.000 0 3 12 7 3.9 19 12 weeks .. . . 14.1 3.1 14 0 :ob0 30 weeks 1 I B, stored 70-80" F. 2.6 13.3 13 6 weeks 0.000 0 0 12.5 2.7 8 12 weeks t4.n 3.1 5 0:ooo 30 weeks 0 2 B. stored 95-10.j0 F 13.i 2.Y A apeks 5 0.000 n (I 13.1 4.4 7 12 weeks 14 :3 3 0 7 0:oon 30 n-eeks 4 '6 ( 2 , stored 40-50c F. 7 . 3 2 . 7 13 6 weeks Ll.000 0 6.2 3.2 12 12 weeks ... 6.6 2.7 13 30 weeks 0:000 3 i:. stored 70--80° F. 7 1 2.6 12 0.000 6 weeks 0 6.2 3.4 14 12 xeeks ... 6.7 0:000 2.8 11 0 30 weeks stored Y6-l0dc F 7 .0 2.6 11 0 ,000 6 weeks 0 6.2 0.8 13 ... 12 aeeks 2.6 1.5 0.000 7 0 30 weeks 0 Total copper values f o r all samples were of t h e order of 0.9 mg./100 grams d r y m u t t e r I Size of unit varies from e m > iiie t o enzyme: cross comparisons are riot valid,
...
...
0
n
... 0
I
..
0 0
..
0
a 0
...
...
0
0
0
0
..
0 1
...
0
4
...
0
...
f
"t7-
io
+++
0
++++
.,.
0
0 0
++
+++
il
0
0
'd
0
0
11
11
0
+
I
...
0
,$
I1 I
..
,..
1
0
0
1
3
f
I
0
0
[I
t++
i
..
4
...
..
values recorded for the fresh vegehble are cxperimttl~t~iliy aignificant. The available iron and tot'al copper data are of no aid in fixirlg the cause of the deterioration noted during the storage periods. However, the total copper content of the potato samples aas about the same as in the samplcs of cabbage 1, and the available iron content of the potato was much less. About 507, of the ascorbic acid was lost during the blanch, a d 50% of the remainder was lost during t'he dehydration procwh. In low-moisture series C the remaining ascorbic acid was considerably more stable during storage than in mdium-moisture sc1ric.s B. Thus, when stored at 95-105" F., t'he 7y0moisturc sampitl became inedible in about 7 months, whereas the 13% moisture sample stored a t the same temperature was undesirable as a food in a little over 1month. The effect of storage temperature 011 tht, retention of ascorbic acid and the development of off-color and odor is particularly noticeable in medium-moisture serios 8. I: seems likely that' t,he low and practically constant values for ascorbic acid recorded for series B during the 30-wcek storage period a t 95-105" F. may be largely due to the development of pigment,shaving a dichlurobenzenone-indophenoltiter. SWEET POTATO
Sone of the dehydrated saeet potato samples tested (Table V) showed an experimentally significant quantity of enzymes, and no positive qualitative test was obtained in any case. The fresh and blanched vegetables were not available for assay, and the dehydrated samples were not placed under controlled storage until several months after they had been processed. Here, a8 in the case of the white potato, no definite conclusions can be drawn from the available iron and total copper (.ontent data. Except for a slight difference in moisture level, the data in Table 5' reveal no significant difference between the two series even though series J was processed about 3 months before series A. The effect of storage temperature on deterioration is again evident from the ascorbic acid data; storage a t 95-105" F. for about 4 months caused a 60% loss in ascorbic acid in both the A and J series, The same general effect of storage temperature is noted also in the carotene content, except that the carotene losses are much smaller than the ascorbic acid losses.
April, 1946
INDUSTRIAL AND ENGINEERING CHEMISTRY
441
series 2 having the more drastio blanch had the shorter storage life. It must be kept in mind, Vitamins Mg./lOO , Enzymes). Units/100 Grams Dry Matter however, that the increased >tois- M ~ . / I ~ o G.~ r 3 ~: a t t e r Ascor- Cate. ture, G. Dry Caro- Ascorbic Peroxi- Cata- bio acid cho- Creso- LacDescription of storage life of cabbage 1 waB Sample yo Matter tene acid dase lase oxidase lase lase case undoubtedly due in part t o the 3 0 1 1 3 J" 5.96 2.2 15.3 29.7 0.000 0.000 1 1 0 3 3 28.3 3.4 14.8 Ad 5.57 presence of sulfite in the J, stored 40-50' F. blanching solution. 2.8 15.7 29.2 5.73 4 weeks Additional evidence that 18 weeks 5.57 2.1 14.3 28.3 o:OOo i 0 0 i i J, stored 70-80' F. drastic conditions of blanching 5.74 4.7 16.0 25.6 ... 4 weeks 2.7 12.4 21.4 18 weeks 5.74 may do more harm than good J, stored 95-105' F. has been obtained inthe Colum5.67 3 . 0 14.6 25.0 4 weeks 18 weeks 5.70 2.0 11.6 11.8 0:OOO 1 4 6 0 1 bia University l a bo r a t o r i e s A, stored 40-50' F. in connection with work on the 5.96 2.8 15.7 30.3 ... 4 weeks 6.63 2.1 14.3 28.3 ... 18 weeks discoloration of dehydrated A. stored 70-80' F. potatoes under contract with 5 66 2 5 14.5 26.5 4 weeks I 0 3 5.83 2 1 12 3 0 000 1 4 20.8 18 weeks the Office of the Quartermaster A, stored 95-105" F. 5 76 4 2 14.1 22 2 4 weeks General. It seems probable 0 0 3 1 0 5 64 2 2 11.1 12.2 0.000 18 weeks that during the blanch and a Total copper values for all samples were of the order of 0.6 mg./100 grams dry matter. possibly also during the drying b Size of unit varies from enzyme to enzyme: cross comparisons are not valid. Lipoxidase values were so low as to be considered insignificant. process certain hydrolytic reSample was dehydrated jn January, received for storage studies in June. actions are initiated, particud Sample was dehydrated in April, received for storage studies in'June. larly when the blanch and dehydration are relatively drastic. Reactive chemical groupings thus liberated during processing may then bring about nutrient If any discoloration of the sweet potato occurred during the losses and color and odor changes during storage which are charstorage period of 18 weeks, i t was largely m'asked by the deep acteristic of deterioration. It seems clear that such chemical orange color natural t o the potato. However, after 4-week storreactions during the storage period are not dependent on enzyme age a t 95-105" F. a marked haylike odor had developed activity, a t least of the oxidative type; the data in the tables which became more pronounced after 18 weeks. show that the rate of deterioration is markedly dependent on ENZYME REGENERATION storage temperature and moisture level. N o experimentally significant evidence was obtained showing ACKNOWLEDGMENT enzyme regeneration during the storage period of any of the deThis study was supported by grants from the Nutrition Foundahydrated vegetables. Values of le& than 10 units of activity per tion, Inc. Acknowledgment is made t o the American Can 100 grams of dry matter are not experimentally significant in the Company, Continental Can Company, F. B. Huxley and Son, cases of those oxidases measured manometrically. As a further Beech-Nut Packing Company, American Foods, Inc., and Drycheck on the possibility of enzyme regeneration, all cabbage Pack Corporation for their cooperation in this investigation. samples after original analysis were placed in storage at two temperatures (room and about -20" F.) and reanalyzed at a later LITERATURE CITED date.' These reanalyses were made after storage periods ranging Adams, M. H., and Nelson, J. M., J . Am. Chem. SOC.,60, 2472 from a few weeks t o several months, but in no case was any sig(1938). nificant evidence of enzyme regeneration obtained. Balls, A. K.,Proc. Inst. Food Tech., 1943,165-9. The data strongly suggest that, under existing commercial Balls, A. K.,and Hale, W. S., J . Assoc. Oficial Agr. Chem., 16, methods of blanching and dehydration, the problem of cabbage 445 (1933). Cruess, W. V., IND. ENQ.CHEM.,35,53 (1943). and potato deterioration during storage, as evidenced by loss in Davis, M. B.,Eidt, C. C., McArthur, M., and Strachan, C. C., ascorbic acid and the development of off-color and off-odor, is not Proc. Inst. Food Tech., 1943,90-8. fundamentally an enzyme problem. That is, the rate of deterioEllis, G.H.,personal communication. ration during storage was found t o bear no relation to the oxidative Elvehjem, C. A., Hart, E. B., and Sherman, W. C., J . Biol. Chem., 103,61 (1933). enzyme content of the dehydrated vegetables. Only in the case Euler, H. von, and Josephson, K., Ann., 452,158 (1927). of the two cabbage series was a significant amount of an oxidative Gregg, D.C.,and Miller, W. H., J . Am. Chem. SOC.,62, 1374 enzyme (peroxidase) found after the blanch. Dehydrated vege(1940). tables containing no detectable amount of oxidative enzyme were Gregg, D. C., and Nelsdn, J. M., Ibid., 62,2500 (1940). Hennessy, D.J., IND.ENG.CHEM.,ANAL.ED., 13,216(1941). found to be as likely t o spoil as those containing small amounts Hill, R.,Proc. Roy. SOC.(London), B107,205 (1930). of peroxidase. No evidence of enzyme regeneration during the Krehl, W. A.,Strong, F. M., and Elvehjem, C . A., IND.ENQ. storage period could be obtained. Furthermore the storage deCHEM., ANAL.ED., 15,471 (1943). terioration does not appear t o be a problem of metal catalysis. Lovett-Janison, P. L., and Nelson, J. M., J . Am. Chem. SOC.,62, 1409 (1940). The discoloration problem of dehydrated potatoes was particuMiller, W.H.,Mallette, M. F., Roth, L. J., and Dawson, C. R., larly important because of the vast quantities processed for the Ibid., 66,614 (1944). armed forces. Moore, L. A,, IND.ENG.CHEM.,ANAL.ED., 12,726 (1940). There is no question but that some type of a blanch is required Nelson, W. L., and Somers, G . F., IND.ENO.CHEM., ANAL.ED., 17,764 (1945). prior t o the dehydration of vegetables containing peroxidase and Parks, R. Q., Hood, S. L., Hurwitz, C., and Ellis, G . H., IND. phenolases; it is well known that these enzymes may cause rapid ENQ.CHEM.,ANAL.ED., 15,527 (1943). discoloration when the vegetable tissue is cut and exposed t o air. Shackelton, L., and McCance, R. A., Biochem. J., 30,582(1936). The discoloration problem during peeling and dicing is serious Snell, E. E., and Strong, F. M., Univ. Te2a8 Pub., 4137, 11 (1941). with certain vegetables. However, it seems possible that the Snell, E. E., and Wright, L. D., Ibid., 4137,22 (1941). drastic blanching conditions frequently specified t o remove the Stotz, E., J . Lab. Clin. Med., 26,1542 (1941). last trace of peroxidase activity may do more harm than good. Sumner, R. J., IND. ENG.CHEM.,ANAL.ED., 15,14 (1943). Some support for this statement is found in the fact ths;t cabbage Thierault, F.R.,and Fellers. C. R.,Food Rasearch, 7,603 (1942). TABLE
v.
ANALYTICAL DAT-4 ON COMMERCIALLYD~HYDRATED SWEET POTATO (STEAM-BLANCHED)
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.
.
.
I
