The VITAMIN C CONTENT of FRUITS and VEGETABLES R, C. BURRELL AND VIRGINIA R. EBRIGHT The Ohio State University, CoIumbus, Ohio rnTRODUCTION
I
N THE rather voluminous literature of this subject
which has grown up in recent years, many factors, both external and internal, have been reported as affecting the Vitamin C (ascorbic acid) content of fruits and vegetables. Much of this work needs further confirmation. However, it is apparent that length of time and conditions of storage, methods of cooking and processing, variety, stage of development, climatic couditions, soils, and fertilizers must be regarded as of significance. These factors affecting the quantity and stability of this vitamin, help explain why reliable investigators, using essentially the same method of determination, have recorded widely different quantities of ascorbic acid in the same kind of fruit or vegetable; For example, Floyd and Fraps (11) report two to six times as much ascorbic acid in cabbage as do Gould and Tressler (13). The results of Tripp, Satterlield, and Holmes (20), Maclinu (16), and Currence (3) with tomatoes might be cited as additional evidence. These investigators report quite different values even for the same variety. Smith and Fellers (4) find marked varietal differencesin the Vitamin C content of apples. That soils can affect Vitamin C content is substantiated by the work of Tressler, Mack, and King (17) who found that spinach grown on upland soil averaged lifty per cent. higher in Vitamin C,than when grown on muck soil. Few data are available concerning the d e c t of stage of development. For ten varieties of peas, average quantities of Vitamin C per gram fresh weight were 0.336, 0.272, and 0.205 milligram for immature, mature, and over-mature samples, respectively (15). The literature of cooking and processing has been reviewed by Fixsen (10) and by Fellers (5). Recent investigations indicate that the most rapid loss of Vitamin C usually occurs during the first two minutes of cooking (6). Discarding the cooking water leads to further loss (7, 8) which may be of considerable magnitude. (See Table 2.) Storage conditions appear to be very important in determining the rapidity of Vitamin C loss. Spinach stored a t lo to 3°C. loses its Vitamin C content quite slowly; but a t room temperature there is a fifty per cent. loss in three days and nearly a one hundred per cent. lossin seven days (17). Fitzgerald and Fellers (9) recently report that fresh suinach on the Boston market varied from 0.15 milli-
gram of ascorbic acid per gram in July to a maximum of 0.68 milligram per gram in November. EXPERIMENTAL
It was thought that i t would be interesting to compare the Vitamin C contents of several garden fresh vegetables with similar vegetables obtained from the open market. Later i t was decided to include samples of certain other fruits and vegetables where comparisons between fresh and market samples could not be made, in order to obtain a rather inclusive list of ascorbic acid contents of fruits and vegetables in which the values were all determined by the same method and by the same investigator. The results of all these determinations are expressed in Table 1. Each value represents the average of a t least two duplicate determinations on each of two separate samples. In the course of the investigation some data were also accumulated on the effect of cooking on Vitamin C content. Girls from the School of Home Economics were told to cook known quantities of certain vegetables so as to obtain palatable preparations. The vitamin coutent of the fresh vegetable was determined immediately before cookmg; and this was followed by a determination of the vitamin content of the cooked material, including the cooking water. The results of these experiments are given in Table 2. For determining the ascorbfcacid content, a modified Tilmans' method (19) was employed. This was essentially the same procedure that has been used successfully by Tressler (18) and his associates a t the New York Agricultural Experiment Station. Results of such determinations have been found to check very satisfactorily with Vitamin C potency as determined by biological assay (17). METHOD OF DETERMINATION
Two 20-gram samples of the plant material were ground in mortars with acid-washed sand and 30-cc. portions of one normal sulfuric acid which also contained two per cent. metaphosphoric acid (12). The latter forms catalytically inactive complexes with copper and iron ions, inactivates ascorbic acid oxidase, and functions as a general protein precipitant to yield a clear solution suitable for titration with the 2,6-dichlorophenol indophenol solution. The presence of strong acid also tends to inhibit rapid oxidative destruction of the vitamin; as well as to retard the reducing action of certain phenols, tannins, and glutathione which sometimes accomuanv the vitamin and which under favor-
TABLE 1 (Codinucd)
Milligrams of ascorbic W i d PI,
Molniol
Asparagus Avocado Banana Beans. snap Beans. s n a p Beans, snap Broccoli Broccoli Brursel's sprouts Brurrel's Sprouts Cabbage Cauliflower Celery (blanched) Chinese Cabbage chive3 Cherry cress cress Cucumbrr currant Dandelion Dandelion Egg Plant Endive (blanched) Endive (green) Garlie Gooreberry Grapefruit Grape Horseradish Kale Kale Kumquat Leek (blanched) Lettuce Lettuce Lettuce Lettuce Lemon Lima BEao Lime Melon Melon. Musk Mustard Greens Nartvrtium Seeds New Zedand Spinach
Okra onion
orange orange
Parsley parsnip paw-Paw Peach Pear Pca Pea Pepper (hot) pepper (green) pepper (ripe) potato Radirh Rhubarb Sage Saldf~ Say Bean (green) Soy Bean (arcen) Spioach Spinach Squash Strawberry sweet corn sweet c o r n sweet potato swi.s Chard lleaves)
Vorir19 Jonathan wolfe River Mary washingtan Unknown Unknown Unknown Tendergreen Unknown Yellow w a r ltalian sprouting Italian sprouting Unknown Unknown Average for t M y varieties Tenderrwee* Primosoow Salt Lake Unknown Unknown Early Richmond water-ere= watercress Chinese Red Lake 'Greens'' (Spring) "Greens" (Summer) Black King Bavarian Bavarian Unknown poorman Unknown Thompson Seedleso Unknown Seofeh Smtch
Unknowm Unknown California Hothouse Mignonette Tennis Ball '.Sunkist'' Hopi Unknown Honeydew Polish No. 1 Unknown Unknown Unknown Long Green Brown "Florida" Navel Paramount Hallow Crown Wild Elberta Kieffer California Telephone Little Marvel Hungarian w a r Windsor A Sunmybrook Early Ohio White lcide mare Unknown Sandwich Island Jown Baorei Unknown Unknown White Bush Clermont Golden Bantam Stowell'e Evergreen Jersey Fordhwk
sovrra
Market F r e ~ b l ypicked Garden fresh Market Market Market Garden fresh Market Market Garden fresh Market Market (Autumn) Market (Winter)
.
Garden fresh Garden f r u h Garden freah Garden fresh Market Garden fresh Freshly picked Freshly picked Market Garden fresh Freshly picked Freshly picked Freshly picked Garden fresh Garden f r u b Garden fresh Market Prerhly picked Market Market Garden freEh Market (Autumn) Market (Winter) Market Market Market
0. s. u.
Gardcn fresh Garden fresh Market Garden fresh Market Market Garden fresh Market Preddy picked Gardcn fresh Garden fresh Mature Market Market Garden fresh Garden fresh Frerhly picked Market Frerhly picked Market Garden fresh Market Garden fresh Garden fresh Market Market Garden f r u h Garden fresh Market Freshly shellrd Freshly shelled Market Garden fresh Market Freshly pieked Market Market Market Garden fresh
E
swiss c h a r d (stems) Tangerine Tomato (green) Tomato (ripe) Tomato (ripe) Tomato (ripel Tomato (ripe) Tomato (ripe) Tvrnip Turnip Greens Zuerhini
Voricl)l
Saurcr
Fardhook Garden fresh Market Unknown Stokerdalc Garden fresh Garden fresh Stokesdale Master Marglobe Garden fresh Garden fresh Small German sugar Market Yellow Plvm Unknown Hothouse Garden fresh Shagoin Shogoin Garden fresh Market Unknown
gram
f i m h wcighl 0.075 0.484 0.180 0.360.57 0.558 0.72 0.262 0.200 0.240 1.214 0 237
able conditions would react with the dichlorophenol indophenol solution. After centrifuging, the residue was washed thoroughly with 30 and 20 cc. of the acid, centrifuging after each addition. The combined extracts were made up to exactly 100 cc. with distilled water and 10or 20-cc. aliquots (which may be diluted to 50 cc. with eight per cent. acetic acid) were titrated with 2,6-dichlorophenol indophenol solution which had been previously standardized against pure ascorbic acid. I n instances where, due to the presence of anthocyanins, the dilution did not dispel a red or pink color which might be confused with the endpoint, aliquots were shaken with small quantities of Lloyd's reagent which was then removed by centrifuging (2). This removes a small quantity of the ascorbic acid as well, but was the best simple method of treatment that could be found for such so1;tions. In actual determinations, 0.1 gramof the 2,6-dichloronhenol indo~henol was weidied out, dissolved in of hot water,-filtered into a 200-cc. small volumetric flask, cooled to room temperature, and made up to volume with distilled water. I n the following discussion this is termed the dye solution. Fifty milligrams of pure-ascorbic acid were then' weighed out and made up to 200 cc. with the above-mentioned sulfuricmetaphosphoric acid solution. Ten-cc. portions of this Vitamin C solution were titrated with the dye solu-
per gram fresh zucigkl.
V~gelnbla Asparnzus Bean* Snap Beans, Lima Brocmli Cabbaee
rncookrd 0.83 0.455 0.297 1.625 1.116
Per can:. 1 0 s of Vi1omin C Cookin%wolrr Cooking ruolcr disconird not dirrorded 26.5 15.0 26.7 12.5 42.2 17.5 61.7 45.3 70.0 55.5
.-..Pear swiss Chard (leaves) Swiss Chard
0.214 0.355
43.1 67.8
21.6 47.3
0.075
58.2
44.8
tion until a faint pink color was observed which persisted for fifteen seconds. From the titration value,
the number of milligrams of vitamin corresponding to a given volume of the dye can be readily determined. Then from the number of cc. of the dye solution which are required for the titration of an aliquot of the unknown solution, the Vitamin C content of the latter may be found The sulfuric-metaphosphork acid solution must be freshly prepared each day. This is also true for the vitamin solution. The dye solution will keep several days but must be restandardized each day. After the solution has been kept for some time, the endpoint assumes a brownish tinge and becomes much less sharp. On standing, the metaphosphoric acid is probably changed to odophosphoric which does not form catalytically inactive complexes with copper or oxidases that otherwise bring about a rapid destruction of the vitamin. For materials suspected of containing appreciable quantities of reversibly oxidized ascorbic acid (which is physiologically available and hence must be determined to obtain the total Vitamin C content), aliquots of the extract should be diluted and treated by bubbling in hydrogen sulfide for ten minutes, followed by carbon dioxide for thirty minutes, or until a test for hydrogen
sulfide is negative (14). This treatment reduces the reversibly oxidized vitamin (dehydro ascorbic acid) to ascorbic acid which will then react with the dye solution. In most instances, the reduction treatment was found unnecessary. No appreciable destruction of the dye by the snlfuric acid used in extraction was observed ( I ) and the blanks were always very small. SUMMARY
The Vitamin C contents of a large number of fruits and vegetables, all determined by the same method, are recorded. Garden fresh specimens of fruits and vegetables contain considerably larger quantities of ascorbic acid than those obtained from the open market. The results here found, like some previous work reviewed in the introduction, indicate that natural variations are mnsiderable; and contribute data which, with those of other investigators, may ultimately permit quantitative expressions of variability, and causes of variation. From the results set forth in Table 2, i t is apparent that a very considerable part of the loss of Vitamin C content that occurs on cooking is due to discarding the cooking water.
LITERATURE CITED
BESSEY, "Vitamin C," I. Am. Med. Assoc.,
111, 1290-8
(1938). BURRELLm MILLER, "The vitamin C content of spring greens," Science. 90, 164-5 (1939). C ~ R R E N"VitaminC ~E, in tomatoes." Market Growers J., 64, 103 (February, 1939).,, FELLERS AND SMITH, Vitamin C content of twenty-one Massachusetts grown varieties of apples," Pmc. Am. Soc.
,lilU1,.
FENTON, TRESSLER, C-,
ANDKING, "Losses of vitamin C during the boiling and steaming of cmats," Food Research, 3, 403-8 (1938). FITZGEWD AND FELLERS, ''carotene and ascorbic acid content of fresh market and commercially frozen fruits and vegetables," ibid.. 3,109-20 (1938). F ~ ~ E"The N .vitamin C content of human foods as affected by processes of cooking and canning," Nvtrition Abrtracts nnd Revs., 8, 281-307 (1938).
(11)
FLOYD AND FRAPS, "Vitamin C content of some Texas
(12)
FUJITA AND IWATAKE, "The determination of vitamin C
fruits and vegetables," Food Research. 4,87-91 (1939).
with 2,6-dichlorophenol indophenol." Biochem. Z., 277, 293-5 .. - (193.5) ~-~--,. (13) GOULDAND TRESSLER, "Vitamin C content of vegetables. 4 (1936). V. Cabbaee." Food Research.. 1. 4 2 7 3~~ , (14) ~ T E S ZDEARBORN, , Am MA'&, "Vitamin C in vegetables. IV. Ascorbic acid oxid&." I. Bid. Chem... 116.. 717-25 (1936). MACKAND TRESSLER, "Vitamin C content of vegetables. 11. Peas." Food Research, 1, 231-5 (1936). MACLINN, FELLERS, AND BUCK,"Tomato variety and strain differences in ascorbic acid content," Proc. Am. Soc. Hort. Sci.. 34,543-52 (1937). :. TRESSLER, MACK,AND KING,"Vitamin C content of vegetables. I. Soinach." Food Resear&.. 1. 1-7 (1936). . . TRUSSLER. Priwte Communmr~~n. 4pril21. 1938. TlL~rnNs,HIKSCH.AYD \'AL'III.I., "The reducing vallre oi olnnr rrssurs and its indicartun of vitamin C." Z. Cnlrr-
"~.
~.
.
.
TRIPP,SATTE~IELD; AND H O L M E ~"Varietal differences in the vitamin C content of tomatoes," 3. Homc Econ., 29, 258-62 (1937).
