August, 1934
I N D U S T R I A L AIVD E N G I I V E E R I K G C H E M I S T R Y
857
through water to remove the r6c values and absorption co”” hydrochloric acid and water efficients obtainable from vapor, and the r e m a i n i n g 2 carbon dioxide was absorbed 2’’ the equation of Bennetch in potassium hydroxide. ga5 and Simmons ( I ) , are listed This provided a quick method in Table I. The coeffifor determining the ethylene S4O dichloride concent,ration in 3 cients have been p l o t t e d against mole flow ratio in the air, as it is easily calcuj Z1C5 lated directly from the carbon 1 5 6 7 8 io Figure 1. dioxide formed. I ~ L LFLOW F A T I O .r Rectification of the exIn Order to determine the FIGURE 1. -4BSORPTION COEFFICIENTS FOR ETHI-LESE DItractor containing various accuracy of this method, a CHLORIDE amounts of ethylene dichlomeasured quantity of air was bubbled through the dichloride produced d i s t i l l a t e s ride in the bubble tower for one hour. The arnount vaporized .with a maxinlum concentration of 0.02 per cent kerosene >.,-.as determined by replacement method and the composition of the air mixture J.,-:Lscalculated from these determinations. The in the Orsnt analyses run on this mixture during the hour remained ACKNOWLEDGMENT substantially constant and checked the determination by the method just described to two decimals in percentage composiThis investigatioll JTas carried out under the Henry Marition. son Byllesby Memorial Research Fellowship in Engineering. The air supplied through the wet test meter had an averLITERSTCRE C I T E D age humidity of 26 per cent a t 20” C. and corrections were lllade for this ia deternlining the dry roluntes used in the (1) Bennetch and Simmons, ISD. EXG.C H E x . , 24, 301 (1932). Long’ Ibid” 22’ 718 (1930). calculations. Each run was in operation for 30 minutes before (2) XIas 16, 1934. any data \.,-ere taken. These data, together with calculated RECEIYED ;=c
0
3.
4
Iodine Reducing Value of Orange Juice Effect of Sodium Benzoate and Heat 11.A. JOSLY?;
AKD
G. L. MARSH,Fruit Products Laboratory, University of California, Berkeley, Calif.
vitamin is novel and, if true,[of great concern to the industry. biological assay, that sodium benzoate and various other The results of the above investigators, howeVer, are contrary substances which had a preservative action against gross to those obtained by Morgan et al. (4) which indicated that fermentation of lemon juice exerted a destructive effect on sodium benzoate in concentration of 0.10 per cent was without vitamin C, two additional papers in which practically the effect on the vitamin C potency of sweetened orange juice. same conclusion is reached have appeared Bennett and Certain results obtained in the course of this study of the Tarbert ( I ) claim as a result of very limited investigations changes occurring during the deterioration of orange juice seem that the use of any preservative which is efficient in prevent- to indicate that the destruction of reducing value and vitamin ing fermentation is followed by a decrease and eventually a C content observed in preserved juices is due tooxidation rather of the indophenol reducing power of lemon than to some little-understood effect of the preservative. Prodisappearance __ longed storage studies made to juice. They conclude th’at in determine the factors involved in untreated juice t h e r e d u c i n g Data reported here show that the iodine rethe darkening of bottled orange factor is protected from atmosducing power of orange juices does not diminish juice indicated that the iodine repheric oxidation by the action a great deal in storage in the absence or presence ducing power of the juice was of a n enzyme which, if inhibited of preservatives andlor heat treatment, provided more rapidly lost under certain or destroyed by t h e usual storage conditions than under oxidation is retarded or prevented f r o m occurring means, results in rapid loss of others. Some of the early data reducing power. Cultrera (2) by such procedures as vacuum-sealing or canning. obtained on the rate of loss of presents data based on 2,6-diI n samples exposed to air the reducing factor is iodine reducing power of the juice chlorophenol-indophenol t i t r a rapidly oxidized. The amount of loss of reducing has some bearing on this particution and on biological assay invalue occurring is conditioned by the amount of lar problem, and i t is therefore dicating that lemon juice prepresented a t this time. Although available oxygen. served with 350 p. p. m. of sulfur the iodine reducing value may dioxide rapidly loses i t s a n t i The writers believe that a n enzyme protecting not be as specific a measure of scorbutic power, thus confirmthe reducing factor f r o m atmospheric oxidation ascorbic acid content of orange ing in part the findings of Bendoes not exist in fresh orange juice but that such juice as 2,6-dichlorophenol-indonett and Tarbert. Although it a protective agency m a y be elaborated in fermented phenol titration, it has recently was early shown that vitamin juice by the causative organisms. been shown that it is fairly reliC is readily destroyed by oxiable in indicatingrelative changes dation, especially a t high temI t is concluded that the loss in reducing value of i n a s c o r b i c a c i d c o n t e n t of peratures and high p H values, orange juice is due to oxidation and that preservathe idea that commonly used orange juice exposed to air (3) tives of the benzoate type or heat treatment in the food preservatives, such a s as in the present investigation. absence of air have no destructizqe action on fhP If this is true, the results resodium benzoate and s u l f i t e s , reducing power. ported here indicate that destrucactually destroy a n t i s c o r b u t i c
S
INCE the report of Williams and Corran ( 5 ) , based on
INDUSTRIAL AND ENGINEERING CHEMISTRY
858
TABLE I. EFFECT OF HEATAND BENZOATE ON THE DECREASE IN IODINE TITRATION OF ORANGEJUICE
Vol. 26, No. 8 WITH
STORAGE
(In cubic centimeters) TREATMENT 0 . 2 % sodium benzoate added Pasteurized at 79.4' C. for 20 min. Pasteurized as above, opened 0 . 2 % sodium benzoate added Deaerated, pasteurized at 7914' C. for 20 min. Deaerated, vacuum-sealed, pasteurized at 79.4' C. for 20 min. 0 . 2 % sodium benzoate added, pasteurized at 79.4' C. for 20 min. Pasteurized as above, opened, 0 . 2 % sodium benzoate added Deaerated, pasteurized at 79.4' C. for 20 min Deaerated, closed under vacuum, pasteurized at 79 4' C. for 20 min.
0 23.0 22.5 22.0 22.5 23.0 20.0 20.0 19.5
7 20.0 18.5 15.0 15,s 22.0 15.0 15.0 16.0
21.0
20.0
- D A Y S STORED AT ROOM TEMPERATCRE 14 28 42 63 178 316 12.0 13.5 13.5 8.5 15.0 14.0 15.0 11.0 10.0 8.5 9.5 8.5 13.0 14.0 14.5 11.0 8.0 9.5 12.0 5.5 8.0 2 50 . 05 177 . 5 1615 20.0 20.0 19.5 12.0 11.0 11.0 10.0 8.0 9.0 11.5 11.5 11.0 9.0 7.5 7.0 14.5 8.0 11.0 9.5 7.0 6.5 19.5
18.5
18.5
20.0
18.5
16.5
7
410 7.0 6.0 4.0 14:5 6.0 415 14.5
TABLE 11. EFFECTOF EXCESSIVE AMOUNTS OF SODIUM BENZOATE AND OF TEMPERATURE OF HEATING ON THE DECREASE I N IODINE TITRATION (In cubic centimeters) SAMPLE L
M N
TREATMENT 2 . 0 % sodium benzoate added Pasteurized at 79.4' C. for 25 min. Pasteurized at 100' C . for 25 min.
0 28.7 27.8 26.5
tion of ascorbic acid in preserved juices is due chiefly to oxidation. I n studying the effect of pasteurization and sodium benzoate upon the color changes occurring in orange juice stored in glass containers, the iodine reducing value was determined on the various samples at periodic intervals throughout the duration of the test. These values, recorded in Table I, represent the amount of 0.01 I\-iodine required to oxidize the reducing materials present in 50 cc. of orange juice. The orange juice was extracted from fruit of the T'alencia variety obtained from the Citrus Experiment Station a t Riverside, Calif. Two lots of fruit a t different stages of maturity, of the following analysis, were used: FIRST
LOT
Total titratable acidity ae % citric Balling degree 20° C . Ratio, Ballingjacid Original iodine value, cc. 0 . 0 1 N 12/50 cc. juice
0.852 12.50 14.7:l 23.0
SECOND LOT 0,656 12.70 19.4:l 21.0
Samples A to E in Table I were prepared from the first lot, and samples G to J from the second. Samples A, B, and C consisted of 200-cc. portions of strained juice placed in 225-cc. crown-capped glass bottles. Sample D consisted of 100-cc. portions in 225-cc. bottles. Sample E consisted of 100-cc. portions of juice packed in 120-cc. wide-mouth jars and sealed with an Anchor closure under a pressure of 15.2 cm. of mercury in a machine designed for this purpose. The size and style of bottles and the quantities of juice in samples G to I were similar to those of A, B, and C, while J corresponded to E in these respects. One bottle of juice was sampled a t each time of analysis. In order to confirm and extend the results obtained in the first test, a second series of samples was prepared one year later. In this test 100-cc. portions of Valencia juice were packed in 195-cc. crown-capped bottles and treated as shown in Table 11. A large amount of sodium benzoate, ten times that added in the previous test and about twenty times that ordinarily used for preservative purposes, was added t o lot L in order to accentuate its effect. In a series of tests conducted to determine the effect of various metallic ions on the flavor and color of orange juice, it was observed that certain cations had a marked effect on color. Some tended to increase the rate of browning and others exerted an inhibitory effect toward color change. Chief among those increasing the rate of browning was Fe-+, while S n + - protected orange juice from color change for longer periods of time. The decrease in iodine reducing values of juices containing 200 p. p. m. of Fe++ added as ferrous sulfate and 200 p. p. m. of Sn++ added as stannous chloride, in comparison with an untreated sample, is shown in
7 22.2 16.5 21.6
D a ~ sS T O R ~AT D R O O MTEMPERATCRE 14 21 28 42 15.9 12.9 11.0 7.8 13.6 8.5 8.0 6.3 8.5 13.8 6.1 4.2
81 5.6 3.3 2.5
274 5.2 3.2 2.5
Table 111. The samples consisted of 130-cc. portions of filtered Valencia orange juice containing 0.2 per cent sodium benzoate, stored in cotton-stoppered 4-liter bottles a t room temperature. The initial iodine titration on all three lots was 19.4; and the addition of Fe+- caused a definite initial decrease, whereas the presence of Sn++ resulted in an increase due to its iodine reducing effect. A 50-cc. portion was withdrawn periodically for titration. The iodine reducing values of a set of experimentally canned T'alencia orange juice samples after storage a t room temperature and a t 0" C. are shown in Table IV. The jul'ce, after deaeration, was flash-pasteurized by passing it through an aluminum coil surrounded by hot water a few'degrees higher than the temperature to which it was desired to bring the juice. The time of exposure to the various temperatures was less than one minute; the cans were completely filled with the hot juice, sealed, and cooled in running water. Since it mas noted that the rate of decrease in iodine reducing value, when all other conditions were constant, was limited by the availability and rate of solution of oxygen, a detailed study was made of the kinetics of the oxidation of juice as determined by iodine titration. Fifty-cc. portions of centrifugalized, freshly extracted Valencia orange juice were shaken in tightly stoppered 250-cc. Erlenmeyer?flasks in a head space of air and of oxygen in a thermostat a t 25' C. The iodine titrations were made periodically. Care was taken to maintain constant conditions of shaking and exposure. The juice for these tests was stored in partly filled 120-cc. containers closed under a pressure of 16.2 to 26.3 cm. of mercury for a few days a t room temperature and afterwards a t 0' C. Since only 70 cc. of benzoated juice were in each container, some oxidation took place. Thus, the iodine titration de'creased from 32.9 to 31.2 in 5 days and remained constant on 4 succeeding days, after which it was used in these tests. Storage a t 0' C. for 157 days resulted in a further slight decrease to 29.0. The results obtained are shown in Figure 1, based on titrations in duplicate or triplicate. A comparison of the decrease in iodine reducing value of freshly extracted navel orange juice, of the same juice after addition of 0.2 per cent sodium benzoate, and after heating a t 100" C. for 3 minutes was made in the same manner by shaking 50-cc. portions of the juice with oxygen for 6 hours. KOmarked difference between the rates of oxidation of these lots of juice was obtained; the values agreed within the experimenal error. Some difficulty was experienced in titrating the oxidized, strained navel juice in the presence of added acid since the end point was green rather than the blue of the starch-iodine. Further tests with samples of benzoates or pasteurized orange juice stored in completely filled bottles did not give
August, 1934
INDUSTRIAL AND ENGINEERING CHEMISTRY
any appreciable decrease in iodine titration after a slight initial decrease, probably because of the oxygen dissolved in the juice.
DISCUSSIOI~ OF RESULTS The role oxygen plays in decreasing the reducing value of orange juice in glass is strikingly brought out by a comparison of the vacuum-sealed samples of Table I which decreased in reducing value only 35 per cent after 410 days of storage, while all other samples except A decreased in reducing value by approximately 65 per cent after 63 days of storage. The variations in the titrations noted for A are, as explained below, ascribable to the presence of mold in certain samples. Slight changes in iodine value occurred in all pasteurized samples during the heating process, except in those which were vacuum-sealed. The greatest reduction in iodine value thereafter occurred during the first 14 days of storage. The limit to which the loss in iodine reducing value occurred was determined by the apparent removal of oxygen from the head space of the bottle. All the samples sealed a t atmospheric pressure a t the time of preparation were under from 2.5 to 7.5 cm. of vacuuni when tested on the sixty-third day of storage. Further evidence that loss in iodine reducing value is an oxidative process was also furnished a t this sampling period. It was noticed that certain samples of A and C were lighter in color than obher members of the same series. Examination showed that these samples had considerable mold growth on the inside cork surface of the crown seal. When the iodine values of the light colored samples were compared with those of the dark colored samples they were found to be considerably higher-e. g., 16.5 for the former and 9.5 for the latter. The mold in this case had apparently competed with the reducing factor for the oxygen in the head space, and this accounted for the observed slower rate of oxidation. The rate and amount of loss in reducing value was also controlled by the amount of oxygen present-that is, by the size of the head space. Samples A, B, and C, as already stated, contained 200 cc. of juice, allowing 25 cc. head space, while sample D, on the other hand, contained only 100 cc. of juice, allowing 125 cc. head space. Sample D, which was deaerated by subjecting the juice to a vacuum of 73.7 em. for 10 minutes prior+to treatment, in order to remove entrapped and dissolve$ oxygen gained during the extraction operation, darkened a t a faster rate and to a slightly greater extent than A, B, or C. This evidence indicates that decrease in iodine number is caused not so much by heating or sodium benzoate as by the oxygen in the head space of the container. Increasing the head space increases the rate of diminution of iodine reducing substances as shown in Table 11. Large amounts of sodium benzoate had no more pronounced effect on loss of reducing valui of the juice than did pasteurization. TABLE 111. EFFECT O F IROX AND TINCATIOSS
ON
DECREASE IN .
TABLE Iv.
CHASGES I S
If anything, the rate of decrease in iodine number was less in the presence of sodium benzoate. Increasing the partial pressure of oxygen by substituting oxygen for air and maintaining the juice saturated with oxygen by shaking, increased the rate of loss of iodine reducing value as shown in Figure 1. The iodine values of canned orange juices, as shown in Table IV, remain practically constant even after storage for one year. The presence of dissolved tin in the juice and the fact that the tin plate maintains a reducing atmosphere in the can probably. account for this. Increase in iodine number
FIGURE1. RATEOF DECREASE IN IODINE REDUCING VALUE ORANGEJUICESHAKEN WITH AMPLE SUPPLYOF AIR OR OXYGEN
OF
due to the presence of dissolved stannous salts is responsible for the relatively high iodine reducing number of canned juice packed in plain tin cans. Increase in temperature of processing had little effect on the change of iodine reducing value. Exposure of a large surface to air resulted in a more rapid rate of decrease in reducing value. Thus, in the data reported in Table I11 the presence of a good supply of air resulted in a more rapid rate of decrease in iodine reducing value, even in the presence of tin, than was found in Tables I and I1 for closed containers. The previous investigators apparently did not control the oxidation of their samples during their tests. They do not indicate whether or not the juices were freed of oxygen and stored out of contact with air. The fact that their preserved juices actually decreased in reducing value indicates that oxidation probably took place. Their use of fermented or fermented and moldy samples as controls may be criticized on the basis that the elaboration of r'educing principles by these organisms, the presence of carbon dioxide in the juice, or removal of dissolved oxygen from the juice by these organisms causes the conditions of oxidation in the control to [ODTNE
REDUCIXG vlLUE
OF ORANGE
JUICE IN
OPET CONT.4ISERS
( I n cubic centimeters)
TREATMENT Clarified 0 . 2 % sodium benzoate added Clarified' 0 . 2 % sodium benzoate plus 200 p. p. m. F e added Clarified: 0 . 2 % sodium benzoate plus 200 p. p. m. S o * + added + +
859
0 19.4
17.0
29.0
D.
