Nutritive Value of Canned Foods FACTORS AFFECTING ASCORBIC ACID CONTENT OF CANNED GRAPEFRUIT AND ORANGE JUICES FRAaK C. L-4MB National Canners Association, Sun Francisco, Calif
C
ITRUS juices have long been regarded as excellent sources of vitamin C (as-
I
The obserbed reLention of ascorbic acid during canning operations varied from 91.6 to 107.5% at three California and four 4rizona grapefruit juice canneries, and from 9i.k to 101.6% at fi\e California orange juice canneries. The aierage retention was 98y0 for both products. During storage at 70" F. for 18 months grapefruit juice lost ascorbic acid at a constant rate of about 1% a month. Orange juice appeared to lose ascorbic acid more rapidlr during the first few months of storage and less rapidly during the following months, but the aterage monthly rate of loss at the end of 12 months was approxiniatelj 1%. DeFiations from the aierage rate were small, and iariations in canning procedure seemed to hate little effect on this rate. Tests for iron, reductones, and dehrdroascorbic acid in stored samples indicated that these substances were either absent or present in insufficient amounta to interfere with the determination of ascorbic acid.
corbic acid) and have been shown to contribute significant amounts of the vitamin to the average American diet. From the standpoint of convenience and economy the canning of citrus juices has made available to the general public a n excellent source of this vitamin. The retention of ascorbic acid during canning operations and subsequent storage becomes of paramount importance in evaluating the nutritional value of canned citrus iuices. Noore, Wiederhold, Atkins, and hIacDowel1 ( I f ) htudied the retention of ascorbic acid in canned grapefruit juice at twelve Florida canneries and found a n average over-all retention of 97y0,. Wagner, Ives, Strong, and Elvehjein (21) conducted similar studies a t trvelve Texas grapefruit juice canneries and found an average over-all retention of 96.595. Ross (16) invcstigatecl tlic; effect of time and temperature on vitamin C retention in canned citrus juices, and several other investigators coiiductcd holding experiments for various times and temperatures ( 4 , 10, 13, 2 1 ) . Other factors affecting the retention of ascorbic acid in citrus juices are discussed by Riester, Braun, and Pearce ( I S ) , and by Wiederhold, At,kins, and Moore ( 2 2 ) . It was the purpose of the present investigation to determine the retention of ascorbic acid during canning operations a t t,hree California and four Arizona grapefruit juice canneries during the 1944 canning season, and at five California orange juice canneries during the 1943 and 1914 canning seasons. These canneries represent the bulk of the citrus pack of California and Arizona. Data are presented on the retention of ascorbic acid i:i citrus juices packed at each of the above canneries after storage for various periods of time at 70" F. Tests were made for substances in canned citrus juices which might interfere with the deterniimtion of ascorbic acid. METHODS OF ANALYSIS
Ascorbic acid was determined by direct visual titration with 2,6-dichlorobenzenoneindophenol,with the following modification of the Bessey and King ( 9 ) procedure:
A 25 nil. portion of juice was made up to 50 nil. with 3Lr, mctaphosphoric acid in a volumetric flask. The contents of the flask were mixed and then filtered. After the first few ml. of filtrate were discarded, a 4 ml. aliquot was titrated with a solution containing 50 mg. of 2,6-dichlorobenzenoneindophenol and 20 mg. of sodium bicarbonate per 100 ml. of solution. The end point was chosen as the first pink color stable for 10-30 seconds. The dye solutions were standardized against 4 ml. of a solution of pure ascorbic acid (Cebione of Merck & C0.j containing 43 1 This is the nineteenth of a series of papers dealing with t h e general cuhjeot. "Nutritive Value of Canned Foods".
860
50 mg. of ascorbic acid (weighed to the nearest 0.1 nip.) per 250 ml. of 1.5% metaphosphoric acid solution. The dye solutions were standardized every day and were discarded after the second day. Since the determinations were performed a t canneries located a t a considerable distance from the lahoratory, samples of dye and ascorbic acid xere weighed into small bottles a t the laboratory. The bottles were then t,ight,ly stoppered ana transported to the canneries where they were opened a8 needed, and the contents dissolved and made up t o volume. to
Brix was determined either by a, Brix hydrometer or a hand refractometer equipped with a sugar scale. The refractometer values were corrected for citric acid according to the method of Stevens and Baier (20) CANNIXG PROCEDURES
The grapefruit was mainly the Marsh seedless variety grown iii the Coachella and Imperial Valleys of California, and in the Salt River F'aliey and Yuma areas of Arizona. A portion of the lruit canned ii; California was transported from Arizona growing arcas. Oranges were the Valencia variety, all grown in the citrus areas of southern California. The fruit was washed and inspected, and the juice extracted either by burring or by passage of the cut halves through corrugated, stainless steel rollers. Burring was accomplished either manually by feeding the cut halves into reamers, or automatically, by means of Brown citrus extractors. Coarse pulp and seeds were removed by passage through stainless steel screens with openings varying from 0.015 to 0.050 inch in diameter. In no case was more than slight pressure applied in screening the juice. After screening, the juice ordinarily was run through a deaerator into a holding tank, where it might or might not be held under vacuum. All of the canneries employed either deaerators or vacuum holding tanks, or both. I n two of the grapefruit juice canneries the juice was heated to about 190" F. in a heat exchanger and then passed immediately through a deaerator. The juice was held in tanks for periods varying from a few minutes to several hours. In one cannery grapefruit juice remained warm (140 F. or more) during a holding period of several hours. In most of the canneries the juice was pasteurized prior to being filled into cans. The cans were cooled immediately either by passage through B tank of cold water or by means of cold viater sprays. L4t one cannery they received additional processing after closing. In tv,-o of the canneries cold juice was filled into cans and sterilized hy rotation under hot water sprays. The grapefruit and orange juices were packed in either S o . 2 or Xu, 303 cylinder cans, with the exception of one lot of grapefruit and one of orange juice packed in S o . 10, and one lot of orange juice packed in 6Z cans. All of the juice was unswcetcned.
August, 1946
INDUSTRIAL AND ENGINEERING CHEMISTRY SAMPLING PROCEDURE
Samples of grapefruit juice or orange juice were taken at each gf several points along the canning line in order to determine the effect of each significant operation on the ascorbic acid content. The points at which samples were taken included the following: tmmediately after extraction, after screening, from the' holding tank, from the filler, and immediately after processing and cooling. It was not possible, nor m s i t deemed necessary, t o take Jamples a t each sampling point a t all canneries, but an endeavor was made to choose the most significant points. Every effort \yas made t o obtain juice representing the same lot of fruit a t each sampling point. I n instances when it was necessary to sample juice over a period of time, such as the time required for a holding tank to fill with juice, one of the following procedures wm used: (a) A number of small samples of juice were taken either at regular intervals or at varying intervals corresponding to the varying rate of flow of juice. If the total sampling time was no more than a feF minutes, the small samples were combined. If the sampling time was longer, each subsample was analyzed separately and the results averaged. ( b ) Juice was siphoned from the line of flow continuously during the sampling period. Because of its stability, juice held for no mor? than 10 to 15 minutes prior to analysis was not preserved with metaphosphoric acid during the holding period. Samples of unscreened juice were taken xhenever it was posJible to get representative samples a t that stage. .4t canneries employing multiple extractors it was frcquently difficult, if not impossible, to secure representative samples before screening, especially with the limited manpower available for this investigation. When unscreened juice was collected, the coarse pulp and seeds were removed by passage of the juice through a small 18mesh household sieve. The juice was stirred but not pressed through the sieve, in a manner approximating as closely as possible commercial screening operation. In one of the grapefruit juice plants (cannery G, Table I) the method of screening differed from that used in the other plants in that the juice was passed over rapidly vibrating screens rather than forced through them. Samples of both screened and unscreened juice were taken a t this plant. Samples were taken from the holding tanks as the juice was being withdrann for canning. It was not deemed necessary to take samples a t this point at plants which allon-~donly a rela-
861
tioely small volume of juice to accumulate in the tanks, and where juice was not held for any appreciable length of time. Samples representing ,juice a t the filler were taken from sealed cans immediately after closure. Hot juice was cooled to room temperature as quickly as possible by immersing the cans in cold running water and rotating or shaking them a t frequent intervals. Juice which was given no further processing after closure was not sampled at the finer, but cans were selected after passing through the cooling equipment. Precautions were observed in the measurement of Brix in citrus juices by the hydrometer and refractometer methods as described by Stevens and Baier (20). I n spit,e of these prccautions it is not certain that the results obtained on undeaerated juice are entirely accurate. A slight apparent increme in Brix may be due in some instances to slightly lo^ results obtained on the fresh samples. The refractometer is regarded as a much more reliable instrument than the hydrometer for determining uniformity of sampling and changes in concentration; it is suggested that thip instrument be used in future studies of this nature. RETENTION DURIIVG CANNING
Data on the retention of ascorbic acid during comxricrcial cauning of California and Arizona grapefruit juice during the 1944 season are shoTvn in Table I ; similar data for California orange juice canncd during the 1943 and 1944 seasons appear in Table 11. Over-all retention of grapefruit juice varied from 91.6 to 107.5%, and of orange juice, from 94.4 t o 101.6%. For both juice3 the over-all retention for all canneries was 98%. These values are in good agreement with those obts,ined by Moore el al. (11) on Florida grapefruit juice and by Wagner et a!.(21) on Texas grapefruit juice. I n several instances retentions apparently in excess of loo'% were obtained. I n fiuch cases, however, the values for Brix usually show a corresponding increase, which indicates either sampling error or a n actual concentration o i the juice. It ie known that concentration did occur in a t least one instance, that of grapefruit juice D3, as a result of deaerating the preheated juice. The l o a retention obtained in grapefruit juice E2 is due to the long holding period in this particular experiment. All retentions are remarkably uniform except in these trvo instances, despite the fact that canning procedure varied considerably from one cannery to another. The data are insufficient to demonstrate that slight dfferences in rctention between ,different canneries are due to variations in canning TABLEI. ASCORBIC JUICE procedure. ACID C'OSTESTO ASD BRIX*OF CALIFORNIA A S D .iRIZON.4 GRAPEFR~IT AT 17.\R10L-S STAGES O F C a N S I S c : Under certain conditions copper accelerates the destruction Coirinierciall>From Over-all Hand Screened Holding Tank Screened From Filler of ascorbic acid. S o n e of the Retention a n ; AEcorbic Ascorbic .Iscorhir hscorbic of dscorbir plants surveyed was observed to nery arid "Brix acid 'Brix acid "Brix acid 'Brix Acid, % contain excessive copper equipA1 .. .. 47.3 11.3 48.5 11.6 103.0 48.7 11.8 2 .. .. 44.6 11.2 . 14.i 11.4 14 8 11.5 100.4 ment, although all of the plants 3 .. 46.9 11.7 .. 48.0 11.9 4i 2 12.1 100.6 contained some copper fittings, B1 41.5 10.3 41.9 10.9 39.4 11.0 10.0 11.3 96.1 such as valves, bolts, etc., to 2 39:9 10:3 , . 39.6 10 3 38.9 10.8 38 6 .. 96.7 49.4 11.6 , . 48 3 12.2 47.0 12 2 4i.8 ,. 96.8 3 which the juice was exposed. c1 4 4 . 5 11.1 .. 41.3 11.1 .. 44 0 10.9 98.9 The obsen-ation was made dur2 44.0 10.9 , . ,. 44.5 11.0 . . 44.1 11.0 100.2 ing the course of this investigaD1 .. .. 48.8 11.4 45.4 11 7 .. 45.0 11.3 98.3 .. .. 39.4 10.5 40.3 10.7 40 0 10.7 101.5 2 tion that, in fresh citrus juice, 3 .. .. 41.6 10.7 45.2 11.5 44.7 11.5 107.5d ascorbic acid exhibits remarkable El .. 43.6 12.4 42.5 12.2 42.1 12.1 96.6 stability undcr conditions which .. 43.1 11.8 40 3 12.0 39 5 11.9 91.6 2 promote its rapid oxidation in F1 .. 40.3 11.2 ,. '39 4 11.8 07 8 2 ., 41.0 11.8 .. 39 I 12.2 9.5.4 other products. D a t a in Table 3 .. .. 42.1 11.6 40.6 12.1 96.4 I11 demonstrate the stability GI 40.7 10.9 40.4 11.1 41.6 11.8 102.2 11.5 43.8 11.5 ., 43.7 12.0 34.8 2 46.1 of g r a p e f r u i t j u i c e e x 3 41.4 11.2 40.2 11 2 , 40.2 11.4 97.1 tracted by commercial proAverage 3 8 . 0 cedures, and of orange juice 2 I n milligrams per 100 ml. Brix u-as determined h r a 115-dronierer in all plant* except C and D u h e r e hand refractometers were used. extracted in the laboratory with Canneries I, B , and C were located in California and canneries D , 'E. F, and G, i n Arizona. d Juice oondentrated by flash boiling nithout return of rondensate. a household juice extractor. Over-all rptention excluded from average. In these tesls the juice was
862
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 38, No. 8
A study was the retention of ascorbic uritl i n a number of samples from ilifi'ereiit sources after various pvriods of storage, for the purCanneryb .Acid. (7 pose of determining the extent .4 1 99 1 t o nhich variations in the raR 2 100.2 42.6 42 8 42.7 12.1 pioduct or in canning procedure B1 38.4 11 0 11.6 101 6 39.8 39.0 11.5 2 a ~ e c tthe retention of ascorbic 12.1 41.9 12.4 99 5 42.5 41.7 12.5 3 12.8 99 5 42 9 42.1 42.3 12.6 12.7 acaid in grapefruit and orange ClC 44.8 45 4 44.3 12.1 98 9 times. 2 .. ii:3 11 3 96 1 53 6 11,: 54.5 52.4 3 .. 10 7 98 5 11.0 4.5 6 lo., 45.9 45.2 From eight to twelve addiDla 52.0 11.5 51.0 11.0 ,. rional cans were obtained from b n5.0 12 5 1: 5410 12:s 98 2" 2a 4S:a 13,'7 45:5 i4:o .. .. rach retention experiment shown b 43:5 13 2 ,. 43:O 13:3 Y8.Yd in Tables I and 11, and the cans 97.9 3 38:8 l2:O 38:5 12.0 , . 38.0 l2:O 38.8 12.2 were shipped to the SanFrancisco 40.5 14.6 95.8 El 40.5 14 5 14.6 40.0 38.8 14.3 2 42.8 42 8 14.4 94.4 14.5 14 4 41 0 40.4 14.5 laboratory where they were Average 98 3 placed in a storage room maina In millisrnnis per 100 nil. b Canneries, A , B, and C were surveyed during the 1943 season and canneries ll and E, during the 194-1heaaon. tained at 70" F. Cans were A hand refractometer was used t o measure Brix in this plant. I n all others a hydrometer was used. Opened after various times for ded Since it proved impossible in these two experiments t o get comparable samples of juice from t h a t ohtained a f t e r screening and t h a t obtained from the holding tank, t h e assumption was made t h a t there waP n o loss hetnepn termination of ascorbic acid conthese sampling points. These values were excluded from t h e average per cent retention. tent. I n most cases two cane were coniposited for a given sampling, but in a few instances only saturated with air during extraction and was held for the ,ipecia slrlgi(. can w a ~used. The results for grapefruit juice and fied length of time without, deaeration. The results of these orange juice are shown in Tables I V and V, respectively. Retentions of ascorbic acid for a given storage period show a studies confirm the findings of several investigators (8, 18, 19) but not those of Floyd and Fraps ( 5 ) . high degree of uniformity for all samples tested. The data for grapefruit juice show a slightly greater degree of uniformity than Wagner et al. (21) noted that commercially strained juice tend* do those for orange juice. There is some indication that the rate to have a slightly higher ascorbic acid content than juice strained of loss of ascorbic acid in orange is more rapid than in grapefruit through coarse gauze. This difference was attributed to the juice during the initial period of storage, and less rapid during higher pulp content of the commercially strained juice. It is a,pparent, therefore, that differences in screening methods might subsequent periods. This, observation is in agreement with Ross produce sliglit, differences in the amount of ascorbic acid present (16), who states: "The data indicate a somewhat greater retention of vitamin C in canned grapefruit juice than in orange juice. in the juice. Preliminary experiments performed in the laboraHowever, the time of half loss is reached at the saint: time for tory showed that grapefruit juice strained through an 18-mesh both, Le., the 2211d month of storage." household sieve in the manner previously described contained pulp n-ithin the range found for commercially strained juice. The data of AIoore et al. (11) do not reveal any significant difference 100 between grapefruit juice extracted with a 24-mesh screen and 20 2 that extracted commercially. U Y 2 " 90 Data obtained a t orange juice canneries D and E do not indiU cate any significant difference in ascorbic acid content of handH 80 extracted and commercially extracted juice. Data obtained at grapefruit cannery G indicate that there might be a difference in 2 ascorbic acid content between the hand-screened and commerY 70 0 2 4 6 8 IO 12 14 16 I0 cially screened juice, but the data are not sufficient to be connltisiw MONTHS OF STORAGE -- - . -. Figure 1. R e t e n t i o n of Ascorbic Acid i n C a n n e d G r a p e f r u i t Juice d u r i n g Storage at 70' F. RETENTION DURING STORAGE TARrx
Ilt,riotls of storage.
TI.
. h ' o R R I P ACIDc' .4SD B R I X b O F CALIFORNIA ORAXGE JVIPE .AT. \'.\RIOlr* C.4XSISG Canned .Juice C'oiunierciall> Fro~n IniniediateljHalid-Svreenui ScrPened Holding T a n k Froili Filler ufter Cooling -___-_ ._ iiscorbic Ascorbic .lacorhi? A9corbir Ascorbic arid 'Brix acid 'Brix :wid 'Brix acid 'Brix acid ' 'Brix 44.1 -14 1 43.7 12.2
ST.\(
It
"f
I)
, .
, .
'' A
In most instances studies on the retention of ascorbic acid during storage were confined to juice from a single source, or to short
T A B L E 111. STABILITY O F ASCORBICACID IS FRESHLY EXTR.4CTED GRAPEFRUIT JUICE AND ORANGE JUICE Ascorbic Acid in Ascorbic Acid in Raw, Screened Same Juice, Tested Juice Tested Period after Holding Immediately, of a t Room Temp.. l'lace of Ascorhio Acid, Holding, Ascorbic Acid, Experimentation Mg./lOO G. Hours 1\Ig./lOO G. Grapefruit Juice Cannery A 47.3 2 47.2 Cannery B 41.5 2 41.5 Cannery D 39.4 21/1 39.6 Cannery E 46.0 51/s 45.9 Cannery F 40.3 3'/C 40.6 Orange Juice Laboratory 39.8
A I 6 . . I
Laboratory Laboratory
75.2 56.4
6
I:\:.-74,"- .9-
56.0
Figure 1 shows the average rate of loss of ascorbic acid for all the samples of grapefruit juice for the first 18 months of storage. The rate of loss bears a nearly linear relation to time; the average ' a month. rate of loss a t 70' F. is approximately 1% Various investigators noted that the rate of ascorbic acid destruction during storage is influenced to a great extent by temperature ( 7 , 16). Lack of data regarding storage temperaturee (IS) or fluctuating storage temperatures (10, 16, 91) render difficult any comparison of results obtained by other investigators with those obtained by the author. It is believed that a loss of about 1% a month may represent the rate prevailing during storage in which temperature averages about 70" F. and does not fluctuate appreciably, B higher rate of loss can he expectt.d if the storage temperature is appreciably higher. TESTS FOR LYTERFERING SUBSTANCES
The reliability of titration for determining ascorbic acid content has been established by the Association of Official Agricultural
INDUSTRIAL AND ENGINEERING CHEMISTRY
August, 1946
863
geiieral interest, because copper is known to influence the rate of destruction of ascorbic hscorhic Acid, IIg. per 100 111, __ Retention, 7; acid. The results are shown . ~.-. Lieforr 1 3 6 I1 18 in Table VI. The ascorbic c:,,,0 u 5 1 3 6 II 18 Codr Locali~\ ning mo. mo. mo. m o . mu. mo. 'no. mo. mo. mo. rno. 1110 acid equivalent of iron, UJ9 9 . 6 9 6 . 9 93 0 88 9 .AI California 47 3 4 8 . 7 4 8 . 4 48 5 4 7 . 2 4 5 . 3 43 3 suming all the iron to be 98.2 9 6 . 4 92.9 8 7 . 9 2 California 4 4 . 6 44 8 4 4 . 6 4 4 . 0 4 3 . 2 4 1 . 6 39 4 98.5 97.0 92.8 87.7 titrated by the dye, shows 46 9 4 7 . 2 4 6 . 5 46 5 4 5 . 8 4 3 . 8 4 1 . 4 3 Califorriie t3; California 4 1 5 40 0 39 2 39 2 3 6 . 8 3 5 . 9 , 9 8 . 0 92 0 8 9 . 8 that there is not sufficient 39.0 98.2 94.6 s 9 . 4 California 39 9 3 8 . 6 38 2 3 8 ' 2 3 7 . 9 3 6 . 5 8 4 . 5 iron present to affect, results 79 5 9 1 . 6 8 8 . 4 9 6 . 1 '97.7 California 44 3 4 4 0 4 2 8 -43 0 4 2 . 3 40 3 38 9 3 5 . 0 ( I to any appreciable extent. In 9 7 , 5 96 1 9 2 . 1 88.7 80 0 -13 0 4 3 . 0 42 4 4 0 . 6 3 9 . 1 35.3 2 Califoriii:s 4.1 0 4 4 , I 111 Arizona -I> 8 4 5 . 0 A.j.6 .44.9 13 i 4 1 . 7 40 1 1 36 4 9 9 . 8 9 7 . 1 9 2 . 7 8 S . 9 80 9 only one case was the amoiiiit ! 0 0 . 0 9 i . 5 93 8 90.0 40 1 4 0 . 0 30 0 37 5 3 6 . 0 2 Arizona 3 9 . 4 40.! ~i iron equivalent to iiiore q9 6 96 9 9 2 . 6 5 8 . 4 44 5 4 4 d 4 3 . 3 4 1 4 :39..5 3 :irizona 41 . 6 4 4 , than 0.5 mg. per 100 granis of I:I Ar/zona 43 6 4 2 . 1 4 1 3 -11 i 4 0 . 6 3 9 . 0 3 7 . 3 .3,3 8 9 9 . 0 96 4 92 Cj 8 8 . 6 80 3 2 .Arizona 43 1 3 9 . 5 39 F 39 d 3 8 . 5 36 9 3 , j . i 32 5 100.0 9 7 . 5 9 3 . i ,S9.!1 8 2 . 3 ascorbic acid. Reductones may be tlisringuished from Rscorbic :wid hy the grcater tendcncy of the latter to combiric with t'ormalclehycle at a pH of aboiit .Iveroni; 9 9 . 2 O i 0 93 0 89 1 S I .li 2.0 (9). Robinson and Stotz ( 1 4 ) develclped a simplified method based on this principle. was amlied - . . t o a number of the i i c o r t i i c .\rid, Zig. PPI' 100 111. __ Rrrentioii, c"c 5amples of grapefruit and orange juices which had IIriore 0 5,s 1 2 5 6 5 12 ( ' d e w.nning mo. nit, I mo. mo. mo. heen stored for 10 and 12 months, respectively, \ l 44 1 43.2 41 5 40 3 95.0 92.2 and also to a few samples of citrus juices stored for 2 42 A 42., 40 ;s 39 2 94.8 91.8 much longer periods a t room temperature; the B l 38.4 89.0 37.8 :34 7 96.9 89.0 2 41.9 41.7 38.7 37.1 92.8 89.7 method failed to reveal the presence of reductones. 3 42.3 42 1 39.4 88 0 93.6 90.3 Dehydroascorbic acid was determined on the C 1 44.8 44.3 41.6 10 6 . 93.9 91.6 aanie samples according to the method of Bessey 47 8 .. 94.5 91.2 2 54.5 52.4 49.5 3 45.9 45.2 12 4 *l.0 , . 93 8 90.7 .. 12). After reduction with hydrogen sulfide, slightly D 1 52.0 54.0 3499 . A8 4 7 . 16 3 91 9 87 2 more dye was reduced, equivalent to 0 to 1 mg. per .. 92.6 87.4 2 45.5 43.0 3 38.8 38.0 35,3 33.3 , . 92.9 87.6 100 grams of ascorbic acid. Since hydrogen sulfide E l 40.5 38.8 30 1 33.9 93.0 87 4 reduction is not entirely specific for dehydroascorbic 2 42.8 40 4 37 3 34.7 , . 92.3 85 9 acid (8), little significance can be attached to the Average 9 4 . 4 91 5 87 1 apparent increase in ascorbic acid. Even under the assumption that all the increased dye reduction is due to dehydroascorbic acid, the quantity present Chemists for fresh arid for recently canned citrus juice ( I ) . The would amount to no more than 1 to 3% of total ascorbic acid possibility that interfering substances form during prolonged prasent. The Roe and Oesterling (16) method for total vitamin C (ascorbic acid plus dehydroascorbic acid) was performed on storage of processed food has been pointed out by various investigators (8, 9, 16). Formation of these substances would give an certain samples. The values obtained by this method were no erroneous picture of the retention of ascorbic acid during storage, higher than those obtained by dye titration. and, since most of these substances behave toward the dye in a I t would appear that the samples t e s t d at the maximum stormanner similar t o that of ascorbic acid, the result might present too favorable an impression of the effect of storage on ascorbic acid. TARLEVI. IROS AND COPPERCOSTENTOF C A N N E DGRAPEFRUITAND Among the interfering substances most likely ORANGE JUICES to be present and to react with the dye, in a .Ascorbic Ascorbic Acid Acid manner similar to that of ascorbic acid, are ferEquivalent Equivalent r o w iron, stannous tin, and reductones. If deIron, of Fe, Copper, Iron of Fe, Copper, Code p,p,x hrg./ioom P.p.x code p . p . x \ I g . / i n o 1x1. P.P.M. hydroascorbic acid were present it R-ould cause low results since this substance does not reCanned Grapefruit Juice duce the indophenol dye, although it possesses vitamin C activity almost equal to ascorbic acid. The experience of this laboratory has been c1 1.6 0 .3 0.4 GI 2.1 0.3 0.6 that stannous tin does not interfere if reasona2 1.7 0.3 0.3 2 1.9 0.3 0.4 ble precautions are observed, particularly in re3 1.6 0.3 0.4 gard to speed of titration. The amounts of D1 1.7 0.3 0,4 2.0 0.3 0.4 2 iron present in samples of grapefruit juice stored ... 3 2.3 0.4 for 18 months and orange juice stored for 12 Canned Orange Juice months were determined by the orthophenanthroD 1 1.6 0 3 0.6 X 1 1.3 0.2 0.6 line method ( 1 7 ) . Two additional lots of orange 2 1.5 0.2 0.9 2 1.3 0.2 0.6 3 1.4 0.2 0.6 juice stored about two years (X1 and .X2) were 1.5 0 . 2 E l 0.7 also tested. Copper was determined on the juice 2 0.7 0.1 0.8 by the carbamate method ( 6 ) as a matter of PEKIOD.IT 70" F. OS ASCORBICACID COXTENT OF TABLEI\-, EFFECTOF STORAGE GKAPEFRL-IT JCICE
~~
~~
['-kXSED
-
principal interfering substances found in food products. I t should llot be inferred that similar results nould have been ohtained had the qamples been stored at higher temptlraturei. ACKNOWLEDGMENT
This investigation was part of t,he Sational Caiirrers Association-Can Manufacturer Institute nutrition program. The author wishes to acknowledge the helpful assistance and advice of E. J. Draper, of the Treesweet Products Company, in the selection of samples, and to thank Anne pressley,Sue Lre, and Donald G. White for their assistance in connection with a substantial portion of t,hr analytical work. LITERATURE CITED (1) (2) (3) 14)
Besaw, 0. .I.,J . Assoc. Ofin'al Agr. Chem., 27, 537-40 (1944). Bessey, 0. A., J . Biol. Chem., 126, 771-84 (1938). Bessey, 0. A . , and King, C. G., Ibid., 103, 687-98 (1933). Fellers, C. R., and Isham, P. D., J . Home Econ., 24, 827-32 (1982). ---, ~
( 5 ) Floyd, W.W., and Fraps, C. S.,Food Research, 7, 382-7 (1942). (6) Greenleaf, C. A., J . Assoc. Oficial A g r . Chem., 25, 385-92 (1942). ( 7 ) Guerrant, N. B., Vavich, M ,G., and Dutrhrr. R. A., ISD. ENQ.
CHEM., 37, 1240-3 (1945).
(1941).
(9)
Jlapson. L. \v., J . .%e. Chem. Itid., 62, 223-32 (l!J4.3;. lloore, E, L , , lvider,lold, aIld iitki,ls, C. D,, s o . 5, 55-7 (1945).
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