INDUSTRIAL A N D ENGINEERING CHEMISTRY
1112
Storage of Defrosted Products
In order to test the keeping quality of the defrosted products, samples [which had been stored a t 7" F. (-13.9' C.) for 300 days] were defrosted and placed in a chill room having temperatures of from 35.6" to 46.4" E'. (2" to 8" (3.). A summary of the results obtained is given in Table I 20
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Vol. 23, No. 10
changed. The juices in the friction-top cans did not ferment, and only a small amount of mold was observed. ilfter standing a t room temperature, however, the products packed in this way were not equal in flavor to those packed in glass. A later set of samples packed in 7-ounce cans with tight closure have been in cold storage for 120 days and so far are highly satisfactory. It is of course recognized that, although no special attempt was made to put up these products under aseptic conditions, it may be impossible to produce material with as satisfactory keeping quality under factory conditions. Conclusions
-40
-
-50
I
I
I
I
I
5
10
15
20
I 25
I
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30
35
40
45
1
50
Minutes Figure 5-Comparison of Cooling R a t e s of Sirup a n d Pineapple Slices a t Center of Jar A-Sirup at center B-Section of fruit a t center C-CaCln bath
After 75 days of this cool storage, the samples showed no marked signs of deterioration, the appearance and flavor of most of them being good. Four jars had developed some surface mold about 1.0 cm. in diameter, but still retained a fair flavor. Sedimentation seemed somewhat heavy, but shaking the packages dispersed the sediment satisfactorily. The juices in crown-cap bottles kept as well as that in jars, and several bottles were removed from the chill room after 36 days and kept at room temperature, 50" to 77" F. (10" to 25" C.) for 35 days, Slight amounts of mold but no signs of fermentation were visible. There was no pressure on any of the bottles, and analysis showed that the total solids and acid had not
Experiments do not show that replacing the air in the head space above the juices or washing out dissolved air with carbon dioxide has any marked effect on the flavor of the juices. Too much carbon dioxide in the juice gives it an off-flavor. With frozen fruits, a slight improvement was noted when carbon dioxide was used; this was marked when friction-top cans were used. Vacuum-packed fruits are better than the ordinary pack. Freezing can readily he carried out in crown-capped glass bottles, 4- or 8-ounce, before or after capping, and in 8-ounce glasses or 12-ounce glass jars, with or without vacuum. Open freezing and freezing in friction-top cans is not recommended unless special precautions are taken for storage out of contact with air. Literature Cited (1) Birdseye, C., IKD. ENc. CHEM.,21, 414, 5 i 3 (1929). (2) Diehl, H. C., U. S. Dept. Agr., Tech. Bull. 148 (1930). (3) Diehl, H. C., Magness, J. R . , Gross, C. R . , and Bonney, V. B . , Canning Age, 11, 217 (1930); Calif. Fruif N c s , 82, 4 (Nov. 1, 1930). (4) Gore, H. C., "Apple Sirup and Concentrated Cider: New Products for Utilizing Surplus and Cull Apples,'' U. S. Dept. Agr. Yearbook and Yearbook Separate 639 (1914). (5) Joslyn, M. A , , and Marsh, G L . , INO.ENG.CHEM.,22, 1192 (1930). (6) McConkie, J. E . , Calif. Fruif N e w s , 81, 5 (Feb. 22, 1930). ( i ) Nelson, P. R . , and Lang, C. W . , Food Znd., 2, 184 (1930). (8) Reynolds, E.S., Fruif Products J . and Am. Vinegar Znd., 10, 143 (1931). (9) Woodroof, J. G., Georgia Expt. Sta., Bull. 163 (1930). (10) Woodroof, J. G I and Bailey, J . E , Z $ i d . , 164 (1930).
Ethylene Treatment of Tomatoes' E. F. Kohman RESEAXCH LABORATORIES, NATIONAL CANNRRSASSOCIATION, WASHINGTON, D. C.
HE ethylene treatment of tomatoes, as well as other fruits, has been given a great deal of attention in scientific and popular literature. Little (2), after calling attention to the use of ethylene with oranges and lemons, says,,"Tomatoes, celery, bananas, and other fruits lend themselves to similar treatment to advantage, and we may even look forward to a time when melons will look even more like melons and taste less like squash." It has been reported by Harvey (I), and colored illustrations are given in substantiation of this, that ethylene tends to ripen the stem end of tomatoes first. Nature tends to ripen the blossom end first. It would be extremely valuable to have tomatoes ripen uniformly on both ends for canning purposes. It seemed logical that if ethylene ripens the stem end first, tomatoes picked when they are not fully ripened and then treated with ethylene gas should result in uniformly ripened tomatoes. Furthermore, if tomatoes could be picked before they are fully ripened, they would stand handling somewhat
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Received May 16, 1931.
better, thus resulting in less broken and bruised tomatoes which are foci for bacterial, yeast, and mold infections. It should be clearly understood that by no known method of ripening, except on the vine, can a tomato be produced equal in quality to a tomato fully ripened on the vine. The advantage for canners in any artificial ripening system would be in avoiding certain damages in handling fully ripened fruit. It may be added, this is equally true of any method of distribution. The quoted statement by Little may therefore give an erroneous impression. A study was made of the effect of ethylcne gas on tomatoes during the tomato season in a canning factory. The temperature ranged from 75" to 80" F. (23.9"to 26.7" C,). To treat the tomatoes with ethylene, a battery of six ash cans, of about 5 cubic feet (0.14 cubic meter) in capacity, were used. These were air-tight except for the cover for which an airtight seal was secured with modeling clay. Through a tube soldered into the cover and carrying a rubber tube with pinchcock, a definite volume of ethylene could easily be introduced.
October, 1931
INDUSTRIAL, A N D ENGINEERING CHEMISTRY
It was always measured exactly in a graduated cylinder of an Orsat gas apparatus. A half vegetable basket of tomatoes was treated in a can a t one time and this was set on a stand to be about in the center of the can. Thus there was free circulation of air in the can. I n every experiment there stood adjacent to each ash can another half basket of tomatoes similar to those being treated with ethylene inside the can. Each morning and evening the ash cans were opened, and, after removing the basket of tomatoes, tipped to empty them of carbon dioxide and to aerate them completely, The tomatoes were again introduced into the can, the cover sealed with the modeling clay, and ethylene again introduced. Although one part in 1000, 2000, and 5000 were used, there was no evidence that the concentration alterbd the nature of the effect. The tomatoes were held in the ethylene-treated atmosphere for a period of 5 days, and when decay was not prevalent, they were subsequently held in the air a few days for further observation. Tomatoes of varying description were used for experimentation. Tomatoes of all stages of ripeness, except those that had developed a full red color as they came into the factory, were sorted for the amount of green surface and subjected to ethylene treatment. Included was a lot having sunburned stem ends. Although several competent judges of tomatoes observed them from day to day, no difference could be noted either in degree of ripeness or development of rot in the treated and untreated tomatoes in any of the lots picked from those coming regularly to the factory. Tomatoes with appreciable green on them ripened equally as well without the ethylene treatment as with it. Sunburned tomatoes showed no improvement in either case. Tomatoes of the Marglobe variety in four stages of ripeness, as judged by the eyes, were then picked in the field. The four stages of maturity aimed a t were as follows: (1) Tomatoes which still had a small area of green. Naturally this was on the stem end. Some of the tomatoes coming to canning factories may be of this stage of ripeness. (2) Tomatoes of which about half the area had become red, the red, of course, being on the blossom end. Such tomatoes are greener than are delivered to canning factories. (3) Tomatoes that were judged to be about to develop red, but on which there was as yet no visible red color. Such tomatoes can be recognized by a yellowish color, verging on red, a t the blossom end. (4) Tomatoes that showed no evidence that they were ready t o develop red color if left on the vines but that were judged to be near that stage.
Ethylene treatment was without effect on tomatfoes in the first and second groups. Those outside the ethylene-treated chambers ripened as rapidly and as fully as the ethylenetreated tomatoes. The history of the third group is interesting and, con-
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firmed by the fourth group, is illuminating as to the effect of ethylene. The tomatoes of groups 3 and 4 that were ethylenetreated began to turn red, all fairly uniformly, and to a noticeable extent in 24 hours. However, all began to redden on the blossom end as tomatoes naturally do, and there was no evidence of reddening on the stem end until the rest of the surface had changed to red. Some of the tomatoes of group 3 outside the ethylenetreated chambers also began to redden visibly after 24 hours, whereas others showed no evidence of it after 5 days. None of the tomatoes of group 4 outside the ethylene-treated chambers showed any evidence of reddening after several days when the ethylene-treated tomatoes of the same group had all become red. Propylene was also used for a few experiments a t the end of the season with an outcome, in general, similar to that obtained with ethylene. However, the experiments do not warrant a comparison of the two gases beyond this. The data obtained suggest the following interpretation. Ii tomatoes are picked when they are ready to develop red color if left on the vines, then ethylene has no appreciable effect on the rate of development of red color on subsequent holding under the conditions studied. If tomatoes are picked so immature that they would not have begun to turn red on the vines for some time, then treatment with ethylene will develop the red color that the tomatoes of their own accord would not have developed. The experiments did not confirm those of Harvey, inasmuch as the red color always devebped first on the blossom end. Tomatoes picked so g e e n that ethylene treatment is necessary to develop red cofor are not suitable for commercial canning. This is true even of tomatoes picked when the first evidence of red color is noticeable. In the author’s experiments, the development of red color on the latter type of tomatoes is not hastened by ethylene. The yield of tomatoes so picked would be materially lower than fully vine-ripened tomatoes. Summary
Ethylene and propylene were found to be without effect on the rate of development of red color on tomatoes unless they were picked a t such an immature stage that they would not have developed red color for some time if left on the vine. Such tomatoes would not be suitable for canning because of low yield and poor quality. The report of Harvey that ethylene treatment brings about ripening on the stem end first could not be confirmed. Literature Cited (1) Harvey, Univ. Minnesota Agr. Expt. Station, Bull. 247 (1928) (2) Little, Science, Nov. 23, 1928.
United States Consumes Half World’s Tin Output Tin is the only metal of which the United States annually consumes more than $20,000,000 worth and yet remains a negligible producer, according t o the United States Bureau of Mines. In fact, the value of the tin annually imported for consumption ranges from $60,000,000 to over $100,000,000 and accounts for almost half of the world production. Annual domestic production is valued a t less than $50,000 and amounts to less than onetwentieth of 1 per cent of the world’s total output. The principal tin-consuming industries are food packing, automobile manufacture, and building. The packing of food is relatively stable from year to year and may be counted upon t o absorb a fairly constant quantity of tin plate and solder, but the automobile industry is subject to wide variation in the number of units produced.
If the recovery of secondary tin-that is, the production of tin from sources other than ore-were included with primary production, the United States would rank third among the tinproducing countries of the world. Tin-bearing alloys, tin-plate clippings, and melting-pot drosses are the most important materials from which tin is reclaimed. Most of the tin recovered from alloys does not pass through a refined-tin stage but is made into alloys which are brought to the required specifications by the addition of virgin metals. Most of the tin plate entering the reclaiming processes consists of trimmings incidental to the fabrication of tin-plate products. In the past some used tin cans have entered the detinning plants but, a t present prices for reclaimed metal, the recovery of t i l l from this source is unprofitable in the United States.
