INDUSTRIAL A N D ENGINEERIiVG CHEMISTR Y
Mav. 1923
527
Oxygen and Perforations in Canned Fruits' By Edward F. Kohman RESEARCH LABORATORY, NATIONAL CANNERS ASSOCIhTION, WASHINGTON, D .
T WAS RECENTLY2pointed out that it is important to exclude oxygen from the can to protect vitamin C in canned
I
foods. This has long been considered an important precaution to minimize the tendency of certain fruits to perforate because of the well-known corrosive action of oxygen on tin plate. I n fact, the longer exhausts and higher closing temperatures that are in vogue a t present are the result of attempts to eliminate oxygen as far as possible. There are no data available, however, which indicate the relative effect of varying amounts of oxygen in the can. It has been suggested that oxygen may have a catalytic effect, and for this reason small amounts might be relatively more harmful than larger amounts. This question is of practical importance because if its effect follows the law of mass action, then the benefits derived from excluding it as far as possible would be commensurate with the pains taken. If, on the other hand, small amounts act catalytically, the problem of its exclusion would be a less promising one. It is common belief that any oxygen left in the can a t the time of closure disappears to a considerable extent during processing and that the last traces disappear within a few days thereafter. This belief has led some to infer that the possibility n being an important factor in causing perforations i slight, although it is admitted that before the oxygen disappears it may start some activity which continues after the last trace is gone. The disappearance of oxygen soon after processing has been generally considered to be due to its combining with some constituent of the food. I n order to obtain more definite knowledge bearing o questions, apples were canned under three sets of conditions so as to bring about a variation in the oxygen content. They ]Presented before the Division of Agricultural and Food Chemistry at the 65th Meeting of the American Chemical Society, New Haven, Conn., April 2 to 7, 1923. 2 Kohman, THIS JOURNAL, 15 (1923),273. TABLEI-GAS
No.
1 2 3 4
5 6
Days Canned
Gas in Total can Total can Total can Total can Total can Total can Headspace Coqtents Total can Headspace Contents Total can
..a ..a
.. , bb ,
3 6
7 8
9
10
11 12
14
3
j (
i
IN
c.
were packed in No. 2 enameled cans, all of which were made from the same base plate. I n Experiment 1 the apples were put into the cans, which were placed under a bell jar and subjected three times to a vacuum of approximately 27 in.; each time the vacuum was released with nitrogen. The cans were then filled with boiling water, exhausted in boiling water for 2 min., closed, processed in boiling water 6 min., and cooled. I n Experiment 2 the apples were also evacuated three times, but in this case t h e vacuum was released with oxygen, and thereafter the qpns were filled with water through which oxygen had bubbled for 1.hr., and which was then heated to 60" C. The apples in this qperiment were also givw an exhaust of 2 min., but they were processed 8 min., to make u p for the lower temperature of the filling water. Under these conditions the gas in the cans a t the time of closure was about 80 per cent oxygen, as against 14 per cent whea, apples are normally canned (Table I). In Experhent 3 the procedure was identical Experiment 2 except that the exhaust was omitted apd that the process was 10 min. to make u p for the lack of exhaust. The cans in these three experiments, about 30 in each, were held% an incubator at approximately 35" C. The first examination was made 6 wks. after they were canned. There ng the cans in Experiment 1, whereas among tho xgeriment 2, 35.7 per cent were eriment 3, 57.6 per cent were perwks., 50.0 per cent of the cans of ed, and 69.7 per cent of the cans in Experiment 3, while there was still no perforation from Experiment 1. Since,ppples,have a p H of about 3.4,this marked effect of oxygen is not in agreement with the views recently expressed by W i l ~ o n . ~ a THISJOURNAL, 16 (19231, 127.
CAWEDAPPLES
n-2/02
5.2 4.9 5.7 6.5
5 8 7 0 8.3 10.2
82 0 76.8
0 7 6.5
0 5 5 1
5.5 38.3
10.0
77.4
7.2
5 6
8.9 15.0
83.2 78.6
0.7 3.4
14.1
79.1
4 1
7.5 7.6
87.4 77.8
0.8 6 0
12.1 7.6 80.4 Normal Apples-Plain Cans ( N o . 2 ) 5.9 89.1 5 0 3.7 86.0 10.3 86.9 8.8 4.3 6.7 0 0 93.3 9.1 1.3 89.6 8.6 1.0 90.4 5.9 0.8 93.3 13.3 1.1 85 6 11.5 1.1 1 1 1.2 0.0 98.8 15.2 1.0 83.8 12 8 0.9 86 3 6.8 0.0 93.2 25.1 1.5 73 4 18.5 1.0 80 5
6.8
0 8 7 8 8 6 1.1 3.0 4 1
43.8 6.8
0 6 2.9
0.6 1.0
9.7 23.6
3.5
1.6
33.3
0.4 2.7
6.4 26.2
0.7 4.3
0.0 0.3 0 3 1.1 0.3
5.0
0.4
37.5
0 1 5.4
7.3 29.5
0.9 5 9
0 0 0.4 0.4 0 0 0.4
6 8
0.4
29.6
9.3 5.2
9.7 13.0 12 6 8.9 6.4
5.6
6.8
12.5 10.3
5 0 14.7
9.8 7.6
7.8
Total can
10.6
Headspace Content$ Total can Headspace Contents Total can Headspace Contents Totalcan
15.1 23.5
20.2 0.0 71.8
89.3 110.0
75.3
82.2 0.0 81.3 101.0 0.0 47.5
Headspace Contents l3 TotaL can 81.5 a Immediately after closing without processing b Immediately after processing and cooling.
-
3.1
5.5
40.6
47.4 12.8 31.2
44.0
32.6 10.0 27.5
36.8 12.4 17.2
528
In work of this kind there are always a number of uncontrollable variables, and it is questionable how far conclusions should be drawn. However, the results were so striking that they suggested further studies. Apples were therefore canned with their normal gas content in plain and enameled cans, and the gas in the cans was analyzed from time to time. The results of the analyses are given in Table I. Determinations were made between the intervals given, but are omitted to conserve space. These figures indicate that the disappearance of oxygen in a can is due, in the case of apples, largely to its combination with the tin plate rather than with the food product. This agrees with the fact that oxygen does not disappear rapidly in enameled cans, as well as with the fact that some oxygen still remains within the apples in plain cans even after 2 wks., although the oxygen was all gone in the head-space after about 3 days. If this view is correct, it offers a plausible explanation for the fact that enameled cans tend to perforate far more than plain cans. It indicates that the length of time that the oxygen remains in enameled cans is proportional to the completeness with which the tin plate is protected by the enamel. The most efficiently enameled cans would therefore not only contain oxygen for a greater length of time, but would have it in greater concentration. Moreover, all the oxygen would be available for the small exposed areas of the tin plate. If we assume that the process of enameling does not bring about a change in tin plate which increases its tendency to perforate, and that the enamel is inert in this respect, then the various facts about perforation can best be explained by assuming that it is largely influenced by some substwce whose quantity is limited and a t times is present only in negligible amounts. We know of no other substance that fits into this condition quite as well as oxygen, although we do not wish
Briquetting. By ALBERTL. STILLMAN. 466 pp. trations.
Vol. 15, No. 5
INDUSTRIAL A N D ENGINEERING CHEMISTRY
159 illusThe Chemical Publishing Co., Easton, Pa. Price,
$3.00. This book is very welcome to any one interested in briquetting, as it gives an excellent picture of American practice and experience. It is well written, well printed, well illustrated, and well indexed. It tells about briquetting fuels, ores, by-products, and metal scrap. The several types of briquetting presses are tersely presented. The story of briquetting steel swarf, turnings, and cast-iron borings is interestingly told, and will be new to many, as will the similar briquetting of light brass and bronze. The chapter on binders is sufficiently comprehensive to show the great variety of materials proposed for use, and the limitations of each. There is a short but interesting chapter on briquetting wood waste. The author is cautiously optimistic in his treatment of peat briquetting, the chapter giving an excellent picture of the development of peat, fuel utilization in America. The treatment of the subject of briquetting of lignite or “Braunkohle” would be improved by bringing out more sharply the distinction between American lignite and German “Braunkohle.” The assumption that our lignite is the equkalent of German “Braunkohle,” and therefore to be treated by the same process has led to much waste of money. The chapter is, however, a valuable resume of the efforts that have been made to improve lignite as a fuel. A readable chapter on the principles of briquetting binders helps to dispel any thought that sticking coal particles together with pitch is a simple art. A history of fuel briquetting in the United States and Canada is given to show the difficulties to be avoided in future construction. The many projects are briefly mentioned, and the causes of failure or suc-
to imply that oxygen is always necessary for perforations t o occur. We have no more evidence for this assumption than for a contrary one, yet it offers a suitable working hypothesis to follow out the ideas suggested herein. I n considering these data, it should be kept in mind that apples are a porous product and by virtue of this condition more gas is occluded than in many other fruits. This may have some bearing on the fact that apples perforate even in plain cans. Approximately one-fourth of the volume of the apples used in these experiments was gas. For this reason no allowance was made for headspace, but instead the cans were filled to overflowing. During processing and cooling part of the gas escaped from the apples to form a headspace. This difference in physical condition of the various fruits is a factor in determining the amount of oxygen that is carried into the can. Finally, the possibility should be kept in mind that some fruits may contain substances which augment certain reactions, but which are not found in other fruits. We need not limit such possibilities to thermolabile substances like t h e enzymes, since Hopkins‘ has found in yeast and animal tissues a thermostable substance, glutathione, which acts as a n oxidation-reduction system.
COKCLUSION Although oxygen in canned apples disappears within a few days after canning in plain cans, in enameled cans it disappears only slowly. This indicates that its disappearance is due to its action on the tin plate rather than a combination with the apples, and is offered as a tentative explanation for the fact that enameled cans perforate more rapidly than plain cans. Oxygen obeys the law of mass action in causing perforations rather than acting as a catalytic agent. 4
J. Biol. Chem., 64 (1922), ,527.
cess indicated. The metallurgist will be interested in the chapters on flue dust and ore briquetting. At the end of each chapter is a comprehensive bibliography of the subject, and there is a better-than-usual index a t the end of the book. The book is an excellent addition t o descriptive technical literature, and should be read by everyone interested in any way in briquetting. 0 . P. HOOD
Division of Biological Chemistry The division of biological chemistry devoted the entire program on Thursday to the symposium on nutrition. The room was packed to capacity the entire day and those in attendance seemed to agree that it was the most interesting and beneficial symposium that they ever attended. Two ideas stood out very prominently in the discussions. The first was that faulty nutrition during the past few years is very largely responsible for the rapid increase of all kinds of nervous disorders, the rapid increase in the decay of the teeth, and the rapid increase in the various reproductive disorders among the American people. The other point brought out in the discussions was that most of the manufacturers of foods, such as the bakeries, the canneries, cereal-food producers, milk condensers, etc., are making every effort now t o put into the dietary of the American people those substances which are known to be essential to health.
J. S. HUGHES,Chairman
