F R A N K C . L A M B Florida canneries and found an average over-all retention of 97%.
Wagner, Ives, Strong, and Elvehjem (21) conducted similar.
studies at twelve Texas grapefruit juice canneries and found an average over-all retention of 96.5%. Ross (16) investigated the effect of time and temperature on vitamin C retention in canned citrus juices, and several other investigators conducted holding experiments for various times and temperatures (4, 10, 18, 21).
Other factors affecting the retention of ascorbic acid in citrus juices are discussed by Riester, Braun, and Pearce (12), and by Wiederhold, Atkins, and Moore (22).
It was the purpose of the present investigation to determine the retention of ascorbic acid during canning operations at three California and four Arizona grapefruit juice canneries during the 1944 canning season, and at five California orange juice canneries during the 1943 and 1944 canning seasons. These canneries represent the bulk of the citrus pack of California and Arizona.
Data are presented on the retention of ascorbic acid in 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 determina
tion of ascorbic acid.
M E T H O D S O F A N A L Y S I S
Ascorbic acid was determined by direct visual titration with 2,6-dichlorobenzenoneindophenol, with the following modifica
tion of the Bcssey and King (S) procedure:
A 25 ml. portion of juice was made up to 50 ml. with 3% rneta- phosphoric 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 con
taining 50 mg. of 2,6-dichlorobcnzenoneindophenol 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 & Co.) containing 45
1 T h is is th e n in e te e n th o f a s e rie s o f p a p e rs d e a lin g w ith th e g e n e ra l s u b j e c t . " N u t r i t i v e V a lu e o f C a n n e d F o o d s " .
The observed retention of ascorbic acid during canning operations varied from 91.6 to 107.5% at three California and four Arizona grapefruit juice canneries, and from 91.4 to 101.6% at five California orange juice canneries. The average retention was 98% for both products. During storage at 70° F. for 18 months grapefruit juice lost ascor
bic acid at a constant rate of about 1% a month. Orange juice appeared to lose ascorbic acid more rapidly during the first few months of storage and less rapidly during the fol
lowing months, hut the average monthly rate of loss at the end of 12 months was approximately 1%. Deviations from the average rate were small, and variations in canning procedure seemed to have little effect on this rale. Tests for iron, reductones, and dehydroascorbic acid in stored samples indicated that these substances were either absent or present in insufficient amounts to interfere with the fractometer values were corrected for citric acid according to the method of Stevens and Baier (20).
C A N N I N G P R O C E D U R E S
The grapefruit was mainly the Marsh seedless variety grown in the Coachella and Imperial Valleys of California, and in the Salt River Valley and Yuma areas of Arizona. A portion of the fruit canned in California was transported from Arizona growing areas. 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 corru
gated, 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 wrere 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 deaera
tor 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. In two of the grapefruit juice canneries the juice was heated to about 190° F. in a heat ex
changer 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 a tank of cold water or by means of cold water sprays. At one cannery they received additional processing after closing. In two of the canneries cold juice was filled into cans and sterilized by rotation under hot water sprays.
The grapefruit and orange juices were packed in either No. 2 or No. 303 cylinder cans, with the exception of one lot of grape
fruit and one of orange juice packed in No. 10, and one lot of orange juice packed in 6Z cans. All of the juice was unsweetened.
860
A u g u s t , 1 9 4 6 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 861 S A M P L I N G P R O C E D U R E
Samples of grapefruit juice or orange juice were taken at each of 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:
immediately after extraction, after screening, from the holding tank, from the filler, and immediately after processing and cool
ing. It was not possible, nor was it deemed necessary, to take samples at each sampling point at all canneries, but an endeavor was made to choose the most significant points.
Every effort was made to obtain juice representing the same lot of fruit at each sampling point. In instances when it was neces
sary to sample juice over a period of time, such as the time re
quired for a holding tank to fill with juice, one of the following procedures was used: (a) A number of small samples of juice were taken either at regular intervals or at varying intervals cor
responding to the varying rate of flow of juice. If the total sampling time was no more than a few minutes, the small samples were combined. If the sampling time was longer, each sub
sample was analyzed separately and the results averaged. (6) Juice was siphoned from the line of flow continuously during the sampling period. Because of its stability, juice held for no more than 10 to 15 minutes prior to analysis was not preserved with metaphosphoric acid during the holding period.
Samples of unscreened juice were taken whenever it was pos
sible to get representative samples at that stage. At canneries employing multiple extractors it was frequently difficult, if not impossible, to secure representative samples before screening, especially with the limited manpower available for this investiga
tion. When unscreened juice was collected, the coarse pulp and seeds were removed by passage of the juice through a small 18- mesh household sieve. The juice was stirred but not pressed through the sieve, in a manner approximating as closely as pos
sible commercial screening operation. In one of the grapefruit juice plants (cannery G, Table I) the method of screening dif
fered 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 where juice was not held for any appreciable length of time.
Samples representing juice at 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 at frequent intervals.
Juice which was given no further processing after closure was not sampled at the filler, 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 de
scribed by Stevens and Baier {30). In spite of these precautions it is not certain that the results obtained on undeaerated juice are entirely accurate. A slight apparent increase in Brix may be due in some instances to slightly low 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 this instrument be used in future studies of this nature.
R E T E N T I O N D U R I N G C A N N I N G
Data on the retention of ascorbic acid during commercial can
ning of California and Arizona grapefruit juice during the 1944 usually show a corresponding increase, which indicates either sampling error or an actual concentration of tire juice. It is known that concentration did occur in at least one instance, that of grapefruit juice D3, as a result of deaerating the preheated juice. The low 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 two instances, despite the fact that canning procedure varied ćonsiderabjy from one cannery to another. The data are insufficient to demonstrate
that slight differences in reten
tion between different canneries are due to variations in canning procedure.
. Under certain conditions cop
per accelerates the destruction of ascorbic acid. None of the plants surveyed was observed to contain excessive copper equip
ment, although all of the plants contained some copper fittings, such as valves, bolts, etc., to III demonstrate the stability o f g r a p e f r u i t j u i c e e x tracted by commercial pro
cedures, and of orange juice extracted in the laboratory with a household juice extractor.
In these tests the juice was
T a b l e II. A s c o r b ic A cid ° a n d Br i x* of Ca l if o r n ia Or a n g e Ju ic e a t Va r io u s St a g e s but not those of Floyd and Fraps (5).
Wagner et al. (S I ) noted that commercially strained juice tends to have a slightly higher ascorbic acid content than juice strained through coarse gauze. This difference was attributed to the higher pulp content of the commercially strained juice. It is ap
parent, therefore, that differences in screening methods might produce slight differences in the amount of ascorbic acid present in the juice. Preliminary experiments performed in the labora
tory showed that grapefruit juice strained through an 18-mcsh household sieve in the manner previously, described contained pulp within t he range found for commercially strained juice. The data of Moore el al. (11) do not reveal any significant difference between grapefruit juice extracted with a 24-mesh screen and that extracted commercially.
Data obtained at orange juice canneries D and E do not indi
cate any significant difference in ascorbic acid content of hand- extracted and commercially extracted juice. Data obtained at grapefruit cannery G indicate that there might be a difference in ascorbic acid content between the hand-screened and commer
cially screened juice, but the data are not sufficient to be con
clusive.
R E T E N T I O N D U R I N G S T O R A G E
In most instances studies on the retention of ascorbic acid dur
ing storage were confined to juice from a single source, or to short
periods of storage. A study was made of the retention of ascorbic acid in a number of samples from different sources after various periods of storage, for the pur
pling, but in a few instances only a single can was used. The results for grapefruit juice and orange juice are shown in Tables IV and V, respectively.
Retentions of ascorbic acid for a given storage period show a high degree of uniformity for all samples tested. The data for grapefruit juice show a slightly greater degree of uniformity than do those for orange juice. There is some indication that the rate of loss of ascorbic acid in orange is more rapid than in grapefruit juice during the initial period of storage, and less rapid during subsequent periods. This observation is in agreement with Ross (16), who states: “ The data indicate a somewhat greater reten
tion of vitamin C in canned grapefruit juice than in orange juice.
However, the time of half loss is reached at the same time for
fruit Juice during Storage at 70° F.
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 rate of loss at 70 ° F. is approximately 1% a month.
Various investigators noted that the rate of ascorbic acid de
struction during storage is influenced to a great extent by tem
perature (7, 16). Lack of data regarding storage temperatures (18) or fluctuating storage temperatures (10, 16, S I) render dif
ficult 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 stor
age in which temperature averages about 70° F. and does not fluctuate appreciably. A higher rate of loss can be expected if the storage temperature is appreciably higher.
T E S T S F O R I N T E R F E R I N G .S U B S T A N C E S
The reliability of titration for determining ascorbic acid content has been established by the Association of Official Agricultural
August, 1946 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 8 6 3 possibility that interfering substances form during prolonged storage of processed food has been pointed out by various investi
gators (£, 9, IS). Formation of these substances would give an erroneous picture of the retention of ascorbic acid during storage, and, since most of these substances behave toward the dye in a manner similar to that of ascorbic acid, the re
sult might present too favorable an impression _______
of the effect of storage on ascorbic acid.
Among the interfering substances most likely to be present and to react with the dye, in a
ble precautions are observed, particularly in re
gard to speed of titration. The amounts of
tinguished from ascorbic acid by the greater tendency of samples of grapefruit and orange juices which had been stored for 10 and 12 months, respectively, and also to a few samples of citrus juices stored for much longer periods at room temperature; the method failed to reveal the presence of reductones.
Dehydroascorbic acid was determined on the same samples according to the method of Bessey (2). After reduction with hydrogen sulfide, slightly more dye was reduced, equivalent to 0 to 1 mg. per 100 grams of ascorbic acid. Since hydrogen sulfide reduction is not entirely specific for dehydroascorbic acid (8), little significance can be attached to the apparent increase in ascorbic acid. Even under the assumption that all the increased dye reduction is due to dehydroascorbic acid, the quantity present would amount to no more than 1 to 3% of total ascorbic acid prosent. The Roe and Oesterling (16) method for total vitamin C (ascorbic acid plus dehydroascorbic acid) was performed on certain samples. The values obtained by this method were no higher than those obtained by dye titration.
It would appear that the samples tested at the maximum
stor-Co p p e r Co n t e n t o f
age times reported in these studies were practically free from all principal interfering substances found in food products. It should not be inferred that similar results wTould have been ob
tained had the samples been stored at higher temperatures.
A C K N O W L E D G M E N T
This investigation was part of the National Canners Associa- tion-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 selec
tion of samples, and to thank Anne Pressley, Sue Lee, and Donald G. White for their assistance in connection with a substantial portion of the analytical work.
L I T E R A T U R E C I T E D