CORRESPONDENCE Vitamins in Canned Foods SIR: In ISDUSTRIAL AXD ENGINEERIKQ CHEMISTRY for July, 1934, page 758, appea:rs an article by E. F. Kohman and others on “Calcium and Vitamin D in Foods.” Its conclusions are based upon two confused variables: (1) the effect of canning upon the nutritive value of foodstuffs and (2) the quality of the foodstuffs fed. Instead of conducting an experiment in which a representative portion of a given foodstuff was fed and another portion canned and then fed, these authors fed raw products from one market, New York City, and fed canned products from the n-orld a t large. No just conclusions can be drawn from such experiments except that they may represent what the average housewife can purchase in New York City. I have considerable faith in these experiments, because I am acquainted with Dr. Kohman and believe he would attempt to select truly representative vegetables from the market. However, I do not believe such reports as this should be published because they may mislead the consumer who may believe the conclusions are valid. There are many opportunities for wrong conclusions from such experiments. For example, during the past year we assayed old and young carrots for vitamin A. The young ones contained only about, half as much vitamin A as the old ones. Suppose t,he man who sold carrots to the New York trade had desired to show t’he superiority of his raw product to canned carrots. The method is obvious. Feed rats a border line allowance of raw, old carrots and compare this with canned young carrots as a source of vitamin A. One could then conclude tha,t raw carrots are superior to canned ones, whereas the canning has nothing to do with the result. In regard to Table I1 of this report, the difference in the original foodstuffs seems obvious. One can only infer that some relation may exist between such a component as cellulose and such an inorganic constituent as calcium. One may conclude either that more cellulose was fed with the raw vegetables or that the more mature vegetables that reach the market have a cellulose content that is less utilized than that which may be canned. The data in Table ’GI, which indicate no differences with and without cod liver oil, are inconclusive because of a lack of a negative control rhich seems clearly needed in this instance. The authors contrast these results with those that occur n-ith and without added oil in the Steenbock diet. They cite data in Holmes’s paper as evidence that his canned food diets had a phosphorus content (0.28 per cent) comparable to the Steenbock diet. They compare their diet with diets n.hich Holmes prepared. Holmes shows, however, that three out of four diets from other laboratories analyzed by him showed phosphorus contents of less than 0.16 per cent. Holmes’s study of the Steenbock diet was actually made because of observations that it 73-as frequently impossible to produce rickets m-ith the diet. In fact the Steenbock diet which Kohman lists in Table V contained only 0.22 per cent phosphorus. Is one justified in assuming that a diet containing 0.28 per cent phosphorus will behave the same as a Steenbock diet that is actually rickets-producing? Steenbock specifies the use of animals low in reserve of the antirachitic factor. Were the animals used by Kohman, which were older than are commonly used on such experiments and thus had an opportunity to build up a reserve, sufficiently free from the vitamin t o reveal a lack over the experimental period? Clearly there is need for proof that the animals used m-ould have developed poor bones if they had received the Steenbock diet a t the same phosphorus level as the canned food to furnish positive
proof that the canned food supplied vitamin D comparable to the level of cod liver oil. This proof could have been obtained, if it act,ually exists, by running a negative control group. In Table V the authors list a Steenbock diet mentioned as used in comparison with canned goods; in commenting on Table VI, they imply that the diet was used as control but there are no data on it in Table VI. I object to the implication in the statement that “the addition of calcium to these foods raised the percentage of bone ash as high as did the addition of milk” without proof that the studies represented by Tables I1 and VI were carried out in a comparable manner. No details are given as to the experiments which produced Table 11. Were the animals used in the two experiments comparable as to age and state of calcium and phosphorus nutrition a t the start? It has been shown that considerable differences in the ash content of bones of rats of the same colony, a t the age they are taken for calcium and phosphorus studies, occur as a result of changes in t’hestock diet and other factors. Killing representative animals a t t’he start is a desirable check when experiments, carried out a t different times and under different conditions, are compared. The fact that the groups under comparison had equally good bones a t the end is inconclusive unless Tve are sure that there was equality a t the start. Such assurance would also be helpful in judging the comparison of the data in Tables VI and VIII. C. M. MCCAY AGRIC~LTUR.AL EXPERIMENT STATION ITAACI. N. Y. November 7 , 1934
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SIR: In commenting on the letter of Dr. McCay, I am expressing my personal viewpoint alone and not that of all or any of the other authors of the paper in question. I have no reason to believe, however, that they would have a materially different vievpoint. Are not the two variables mentioned by McCay in the first paragraph beside the point of the article as expressed in its first paragraph? I would regard as foolish anyone who has available fresh fruits and vegetables from his own orchard and garden who would use canned foods. I see no practical reason for making a comparison between the two. I would regard as equally foolish anyone mho would purchase raw products from the city markets to can for nutritional advantages-that is, products that have been shipped from afar or held in cold storage for appreciable periods. If we want peas for dinner tonight, we can either buy a can of peas or purchase raw peas from a city market and have them cooked. If we are interested in the nutritive value of the peas, a comparison b e h e e n these two would be all that lvould be of practical value. Dr. McCay misstates the conditions when he says the comparison was between canned and raw foods for it was actually between canned, home-cooked, and raw foods, the last two representing the same foods. In McCay’s own words, we have covered “what the average housewife could purchase in New York City.” INDUSTRIAL AND ESGINEERING CHEMISTRY readers are capable of judging how well New York conditions represent conditions in other cities. McCay has cited nothing in evidence to show the conclusions are not valid. The statement in McCay’s third paragraph that there are many opportunities for misrepresentation in such experiments is certainly true. It will simply be up to each reader to decide whether we have misrepresented. There seems to be little point. to Dr. McCay’s remarks about Table 11. If one could always present full and complete explana-
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