The thiamine or vitamin B, concentration in milk does not appear to be affected by the diet of the cow---probably because the vitamin is synthesized in sufficient amounts in the paunch of the cow to supply much of that required for the production of milk. The thiamine content of milk is relatively high early in lactation. Dr. Kon and his coworkers at Reading, for example, found that colostrum contained 0.60 to 1.00 mg. of thiamine per liter; that early milk contained about 0.6 mg., and that milk produced in mid- and late-lactation contained 0.3 to 0.4 mg. per liter. Kon has since given the average thiamine content of milk as 0.36 to 0.45 mg. per liter.
P. B. Pearson and A. L. Darnell of the Texas Agricultural Experiment Station found 0.56 to 0.58 mg. of thiamine per liter in milk produced during the first 9 days of lactation, and 0.38 mg. after the same cows had been in milk for 30 days. They arrive at an average of 0.38 mg. per liter for milks from 25 cows sampled separately after the first 30 days of lactation. Figures outside of these ranges have been obtained by various methods; it seems that an average of 0.4 mg. per liter is probably a fair estimate.
Thiamine is less stable toward heat than riboflavin and some of the other B vitamins, but the amount lost in the pasteurization of milk varies with the method used. Thus, Holmes and co-workers found 9.1 percent and Kon estimates that on an average about 10 percent of the thiamine in milk is destroyed when in pasteurization the milk is held for about 30 minutes at about 145 F.; Holmes found a negligible destruction (2.8 percent) when milk was pasteurized by heating at 161' to 181 ' F. for 22 seconds.
Nicotinic acid has been found to be synthesized in the paunch of the cow. Various research workers have reported values for the average nicotinic acid content of whole milk which range from 0.6 to 1.1 mg. per liter. Most of the values were obtained microbiologically; quite variable results have been reported by chemical methods sometimes several times those given above.
A. E. Schaefer, J. M. McKibbin, and Dr. Elvehjem obtained much higher results for the niacin potency of milk, using niacin-deficient dogs. They concluded that a synthesis of niacin must take place either in the alimentary tract or the body tissues of dogs, and that "the effect of the milk must be related to specific precursors of nicotinic acid or to the protein content of the milk."
Subsequent papers have appeared that throw light on this problem, but a full understanding of the significance of these results apparently awaits further work.
Work has been done on the pantothenic acid, pyridoxin, biotin, inositol, choline, and folic acid content of milk. It is interesting to note their presence in this food.
Vitamins A and D occur in the fat of milk and, therefore, the value of skim milk and skim-milk products as sources of these nutrients would be negligible, but neither these vitamins nor riboflavin are destroyed in pasteurization, spray drying, roller drying, or in the making of condensed or evaporated milks. The effect of these processes upon the nutritive value of the protein in milk is generally negligible. Only with thiamine (vitamin B1) and ascorbic acid are the losses considerable; and, as we have noted, the losses can be largely reduced in some instances by proper methods of processing. There is no evidence that the utilization of the calcium in milk is affected by any of the methods of processing we have mentioned.
C. A. Cary joined the Bureau of Dairy Industry as a chemist in 1917, and engaged in research problems in biochemistry and nutrition. Since 1940 he has been head of the Division of Nutrition and Physiology in the Bureau.
A. M. Hartman, a chemist in the Bureau of Dairy Industry since 1924, is engaged in research problems in biochemistry and nutrition.
by C. A. CARY and A. M. HARTMAN
REMARKABLE progress has been made in identifying the nutrients in our foods and feeds, but results of work in various laboratories indicate that there are still other unidentified constituents in some foods and feeds that may play an important role in nutrition.
Altogether, the findings with the rat, mouse, dog, monkey, and the human constitute a body of evidence that should be regarded realistically in considering the question of whether we are well fed.
Here we shall present evidence obtained in the Bureau of Dairy Industry laboratory at Beltsville that we believe demonstrates that :
Milk and certain other foods and feeds contain an unidentified nutrient ;
White flour, enriched white flour, whole-wheat flour, yeast, and certain other foods and feeds do not contain this nutrient;
When the young are deprived of this factor and then are fed a diet containing all known nutrients in adequate amounts or a diet containing these nutrients along with white flour, enriched white flour, whole-wheat flour, or yeast, their growth and development is by no means normal and under certain circumstances is impossible, unless they are supplied in some way with this unidentified factor.
The nonfat solids of milk are a good source of protein, calcium, and riboflavin, and contain other salts and known water-soluble vitamins Of value in nutrition. These nutrients supplement the foods used as our principal sources of energy, such as bread, butter, oleomargarine, sugar, cereals, and so on. We believe, however, that these foods can be supplemented with all of these nutrients or with all known nutrients and not produce the effect on growth, for example that is produced by supplementation with milk itself or with dried skim milk. What we have said here about flours appears to be true of the grains in general; they are deficient in this unidentified nutrient. With livestock, this unidentified nutrient is supplied by roughages and leafy feeds.
In one experiment, we fed rats as much as they would eat of certain, rations, as follows:
Group 1. A basal ration containing adequate amounts of all known nutrients;
Groups 2, 3, and 4. The same basal ration, containing 45.5 percent of white flour, enriched white flour, or whole-wheat flour, respectively, in place of carbohydrate;
Groups 5 and 6. The same enriched white flour and whole-wheat flour rations as fed to groups 3 and 4, except that the ration contained 10 percent of dried skim milk.
All of these rations contained amounts of all known nutrients that should be adequate for optimum growth. Nevertheless, the average growths of the rats in groups 1, 2, 3, and 4 were all about the same, and were not much more than half that of their sex-litter mates in groups 5 and 6, which received the dried skim milk. There is no question about the statistical significance of these results; we shall consider their interpretation and significance relative to the nutritive value of milk.