the value of cocoa and chocolate as sources of protein in the diet. the united

THE VALUE OF COCOA AND CHOCOLATE AS SOURCES OF PROTEIN IN THE DIET.

BY H. H. MITCHELL, JESSIE R. BEADLE& AND M. HELEN KEITH.

(From the Division of Animal Nutrition, Department of Animal Husbandry, University of Illinois, Urbana.)

(Received for publication, October 11, 1926.)

The United States for many years has been the largest im- porter of cacao and cacao products, and since the war an enor- mous increase in such imports has occurred. Thus, for the period 1910 to 1914, the average yearly importation of cacao products was about 145 million pounds. In 1920, the importation was 345 million pounds, increasing in 1923 to 417 million pounds, at which level it has been approximately maintained to the present time.

Cocoa and chocolate are manufactured from the bean of the cacao tree, Theobroma cacao. The fruit of this tree when ripe consists of pods 7 to 10 inches long containing from 20 to 50 cocoa beans. At harvesting, the pods are opened and the pulp and seeds removed. The latter are then generally subjected to a fermentation process (1) involving the action of yeast as well as of bacteria in order to facilitate the removal of the pulp from the beans and to develop their characteristic color and aroma. Subsequent to this fermenting or “sweating,” the beans are prepared for market by washing, drying, and occasionally by polishing. Probably the most important individual process in the manufacture of chocolate and cocoa relates to the roasting of the bean. The roasting is very carefully con- trolled, the temperatures employed ranging from IOO-135°C. During this process the aroma of the bean is further developed and the husk is rendered readily removable from the remainder of the seed. After roasting the beans are cracked and the broken husk separated from the nibs by winnowing. During the process the germ is also removed by sieving. The nibs are ground to a fine powder, and, if they are to be used in the manufacture of chocolate, they are pressed into cakes after admixture with sugar and proper flavoring materials. If they are to be used in the manufactureof cocoa they are submitted to pressure in hydraulic presses which remove from 60 to 70 per cent of the cocoa butter. The original nibs contain from 45 to 50 per cent fat, while the cocoa powder contains from 25 to 35 per cent.

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Protein Value of Cocoa and Chocolate

The average composition of cocoa as it is found on the Ameri- can and English market is given in Table I. The nitrogenous compounds in cocoa have been investigated by Stutzer (2), who found in a sample of cocoa untreated by chemicals that theobromine accounted for 16.6 per cent of the total nitrogen, ammonia for 1.4, extractives for 6.3, and proteins for 75.9 per cent. The protein content of the cocoa was further subdivided on the basis of its solubility by animal enzymes. On this basis 44.6 per cent of the total nitrogen of the cocoa was present in the form of digestible protein and 31.3 per cent in the form of indigestible protein.

TABLE I.

Reported Average Analyses of Cocoa in America and England.

English ana1yses.t

Moisture ............................. 6.23 3.cs.o Protein .............................. 18.34 19.0-20.0 (N X 6.3) Fat. ................................. 26.69 26.0-31.0 Ash .................................. 5.49 3.9-8.8 Starch ............................... 11.14 2.7-7.3 Fiber ................................ 4.48 6.8-7.2 Theobromine ......................... 1.15 1.7-2.0 Caffeine .............................. 0.16 Other N-free substances .............. 26.32 29.cGg.o

* Reported by Winton, A. L., Bailey, E. M., and Silverman, M., in Corm. Agric. Exp. Sta. 27th Ann. Rep., 1903, 125.

t Reported by an anonymous writer in Lancet, 1905, i, 47.

The solubility and digestibility of the nitrogenous compounds in cocoa are important considerations in any determination of the value of cocoa and chocolate as sources of protein in nutrition. In 1900 Forster (3) reported the results of chemical and physiological investigations of the nitrogen compounds of Dutch cocoa. Of the total nitrogen in this cocoa 44.5 per cent iwas soluble in water, 15.6 per cent was insoluble in water but was rendered soluble by art,ificial enzyme digestion, while 39.9 per cent was insoluble in water and indigestible by enzyme action. 5 years later an anonymous contributor in the Lancet (4) reported similar tests on English cocoas, the results of which indicated


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Mitchell, Beadles, and Keith 17

that 33 per cent of the nitrogen of untreated cocoa was soluble in water and that 68 per cent was digested by pepsin and pancreatic juices.

The results of such tests as these indicate that a considerable fraction of the nitrogen of chocolate and cocoa exists in the non- protein form, mainly as theobromine, and that of the protein in these products a large share cannot be brought into solution by animal enzymes. The indigestibility of much of the nitrogen of cocoa is further confirmed by animal experimentation. Schles- inger (5) cites digestion experiments by Weigmann upon himself showing that only 42 per cent of the nitrogen of cocoa is absorbed. In 1895 Cohn (6) also determined the digestibility of cocoa nitrogen by in vitro experiments as well as by digestion experiments on human subjects. He found that gastric and pancreatic digestion in vitro dissolved about 53 per cent of the nitrogen of cocoa powder. When cocoa was included in the mixed diet of human subjects, it was estimated that 53 per cent of its nitrogen remained undigested. Similar experimental results pointing to a low digestibility of cocoa nitrogen have been reported by Pin- cussohn (7) and by Neumann (8). In contrast to most of the published experimental data of this nature, Forster (3) cites human digestion experiments by Bruns which have been inter- preted to mean that about 80 per cent of the nitrogen of cocoa is digested when consumed with milk.

In so far as the authors are aware, no experiments have been reported in the literature relating to the biological value of the nitrogen of chocolate and cocoa; i.e., the maximum utilization of the absorbed nitrogen in metabolism. Furthermore many of the results reported on the digestibility of the nitrogen of these foods in vivo are in all probability only approximately correct, since they have been arrived at indirectly from results obtained with a mixture of nitrogen-containing foods.

The experimental data to be reported in this paper were obtained from a series of thirty rats fed rations in which ether- extracted cocoa powder supplied practically all of the nitrogen, or in which a definite mixture of skim milk powder and ether- extracted cocoa powder provided practically all of the nitrogen. The investigations consisted of nitrogen balance studies so de- signed as to obtain information on the biological value of the ab-


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18 Protein Value of Cocoa and Chocolate

sorbed nitrogen as well as on the digestibility of the nitrogen as consumed.

Experimental Results.

The methods used in the metabolism experiments relative to the preparation of rations, the feeding of the rats, and the collection of the excreta have already been described in earlier reports (9) of similar experiments from this laboratory. In the initial and final standardizing periods, in which the relation of metabolic fecal nitrogen to the food consumed and of the endogenous nitrogen to the body weight were determined, the rations contained a small amount of dried ether-extracted whole egg to furnish from 0.70 to 0.75 per cent of nitrogen. In the test periods the nitrogen-containing constituents consisted of dried ether- extracted cocoa powder or of dried skim milk or of a mixture of the two in such a proportion that each food contributed 50 per cent of the nitrogen. In these test rations enough of the nitrogen-containing materials was included to furnish from 1.30 to 1.35 per cent of nitrogen (approximately 8 per cent of crude protein). The other constituents of the ration consisted of 4 per cent of the Osborne and Mendel salt mixture (lo), 10 per cent of centrifuged butter fat, 4 per cent of Cellu Flour,l from 10 to 30 per cent of sucrose, and enough starch to make up 100 per cent.2 The ingredients were mixed with water and cooked in a double boiler. After being dried and ground finely, the rations were analyzed for nitrogen.

Besides its allotment of the experimental rations each rat received daily 25 mg. of yeast vitamin (Harris) as a source of vitamin B and 1 to 2 drops of cod liver oil. The amount of vitamin B concentrate fed contained from 2 to 3 mg. of nitrogen, which has been neglected in the calculation of the coefficients of digestibility and of the biological value of the dietary nitrogen.

The cocoa used in these experiments was a common brand (Hershey’s), which was found by analysis to consist of the follow- ing constituents: moisture 3.63, ether extract 24.63, ash 4.91,

1 A product obtained from the Chicago Dietetic Supply House containing by actual analysis, 37.8 per cent crude fiber and only 0.015 per cent of nitrogen.

2 In the later experiments 1 per cent of NaCl was included in therations.


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Mitchell, Beadles, and Keith

nitrogen 3.83, crude fiber 6.84 per cent, and gross energy 5.57 calories per gm. A theobromine determination by the Decker- Kunze method gave an exceptionally high value of 2.83 per cent. This cocoa powder was continuously extracted with ether for 48 hours or longer before being used in the experimental rations, in order to remove at least the larger part of the contained fat.3 It has always been considered a wise plan in performing these metabolism studies to insure that the rations to be compared are approximately equal in calorific value.

The complete data of the nitrogen balance experiments with the resulting biological values are given in Table II.

The biological values calculated for these different rations presumably represent the percentage of the absorbed nitrogen used by growing rats for both maintenance and growth. Their calculation involves the assumption that the excretion of fecal nitrogen per gm. of food consumed on the low nitrogen ration in the first and final periods measures the excretion of body nitrogen in the feces in the intervening periods. Any change in the excretion of the fecal nitrogen per gm. of low nitrogen ration from the first to the final period is assumed to occur in a linear fashion with respect to time. The second assumption involved in these calculations is that the excretion of nitrogen in the’urine per 100 gm. of body weight in the first and final periods of low nitrogen feeding is a measure of the excretion of body nitrogen in the urine in the intsrvening periods, any change in these values from the first to the final period being also assumed to be linear.

The reasoning upon which the calculation of the biological value is based may be illustrated by a concrete case; namely, that of Rat 334 in Period II. In 7 days comprising this collection period, this rat consumed an average of 5.6 gm. of food daily containing 73 mg. of nitrogen exclusive of that consumed in the vitamin B concentrate. The fecal nitrogen for the period averaged 56 mg. per day, of which it is estimated that 11 mg. were contributed by the body. Therefore, 45 mg. may be considered as representing indigestible food nitrogen. On this assumption, the absorbed nitrogen amounted to 73 - 45 = 28 mg. per day. The average daily excretion of urinary nitrogen was 34 mg. Since the endogenous metabolism of the rat was estimated to have resulted in the excretion of 13 mg. of nitrogen in the urine, the difference between this figure and the total urinary nitrogen, namely 21 mg., may be considered as resulting from the exogenous metabolism of the cocoa nitrogen. Since 28 mg. of the cocoa nitrogen were absorbed and 21 mg. were excreted in the urine, approximately 7 mg. may be considered as having been retained in the body for maintenance and growth. This amounts to 26 per cent of the

3 Examination of the ether extract showed it to be practically free of nitrogen.


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TABLE II.

Nitrogen Metabolism Data and Biological Values.

Rat No. 1 $$i;;. / 2s;. 1 i;;;& 1 inzkke. j “$;’ 1 -$ftTy (“t$f;’

Period I. Egg ration, containing 0.74 per cent N.

331 332 333 334 335

gm. gm. gm. nzg. mg. wl. per cent 61 67 8.0 14 17 59 65 8.0 14 17 59 65 8.0 15 16 59 63 8.0 15 18 58 62 8.0 15 17

Period II. Cocoa ration, containing 1.29 per cent N.

331 332 333 334 335

52 48 5. 4 69 54 32 22 51 47 5.2 67 53 29 34 51 49 5.1 66 49 30 33 53 49 5.6 73 56 34 26 50 48 5.7 74 54 33 35

Period III. Egg ration, containing 0.74 per cent N.

331 332 333 334 335

55 56 5.7 12 11 54 52 4.9 10 15 57 58 5.8 13 11 55 56 5.8 12 13 56 56 5.6 11 14


341 342 343 344 345

63 67 8.0 15 22 60 63 7.9 15 20 61 63 8.0 15 62 64 8.0 14 20 65 67 8.0 16

L 19

20 -

Period II. Cocoa ration, containing 1.29 per cent N.

rm gm. gm. ml. ml. WT. per cent 341 56 50 5.8 75 58 33 41 342 52 48 6.8 88 59 28 66 343 54 48 5.7 74 40 31 65 344 53 44 5.6 72 60 28 47 345 55 50 5.9 76 63 30 38


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TABLE II-Continued.

Rat No. 1 2%;. 1 2;;;. ( $z& / in&. / “$ / Ur$Fy I”;$$$


341 342 342 344 345

56 63 6.8 13 17 54 57 7.0 12 14 55 56 5.7 14 14 54 55 5.3 13 16 57 61 6.1 16 12


361 362 363 364 365

70 85 8.0 22 18 70 72 7.8 18 16 89 94 8.0 20 20 68 77 6.4 22 15 81 87 8.0 20 20

Period II. Milk ration, containing 1.35 per cent N.

361 92 100 8.0 108 30 38 82 362 79 89 6.8 92 24 34 80 363 98 106 8.0 108 29 36 84 364 86 95 7.0 95 24 29 87 365 90 100 8.0 108 30 34 87

Period III. Cocoa-milk ration, containing 1.35 per cent N.

361 362 363 364 365

98 97 8.0 108 52 43 86 85 7.3 100 61 41

106 108 8.0 108 57 42 93 95 7.9 107 62 38 99 98 7.9 107 61 41

Period IV. Cocoa ration, containing 1.31 per cent N.

68 55 68 68 68

gm. gm. gm. ml. ml. fw. per cent 361 91 80 5.4 71 57 31 44 362 72 68 4.6 60 46 32 17 363 101 94 6.2 81 70 34 27 364 88 78 4.3 56 48 28 24 365 93 82 4.8 63 66 30


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TABLE II-continued.

Rat NO. 1 ~~~~. 1 ~~~~. 1 ~~~~~~ 1 inure. 1 “~” ( unlay IB~~~~’

Period V. Egg ration, containing 0.72 per cent N.

361 86 I 81 1 3.6 1 362 Died at end of Period IV*

I; ‘ii 1 ‘E / 3;: / ;; ;;


391 119 115 6.5 17 24 392 123 114 5.6 14 30 393 115 112 6.4 16 24

394 117 112 5.9 14 26 395 115 108 5.6 15 26

Period II. Cocoa-milk ration, containing 1.28 per cent N.

391 114 119 8.0 103 53 36 77 392 112 115 8.0 103 54 36 78 393 110 113 8.0 103 51 38 73 394 110 111 8.0 103 55 36 74 395 107 110 8.0 103 51 38 75


391 125 125 5.4 11 18 392 120 112 6.4 11 16 393 118 119 6.1 12 16 394 116 120 6.7 12 15 395 115 113 4.7 10 15

* In estimating the body N in the feces and urine of this rat in Periods II to IV, inclusive, it was assumed that the variations in the metabolic N in the feces per gm. of food consumed, and in the endogenous N in the urine per 100 gm. of body weight, were the same as the average variations for the other four rats in the group.


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TABLE II-continued.

Period I. Egg ration, con&ning 0.67 per cent N.

gm. gm. gm. ml. mg. m7. per cent 401 78 84 7.9 14 13 402 77 79 6.8 16 13 403 77 79 7.5 16 13 404 75 79 7.5 17 12 405 71 75 7.2 15 12


401 402 403 404 405

84 89 7.5 96 50 27 82 87 8.0 103 58 30 81 85 7.9 102 54 29 79 80 6.8 87 50 25 78 77 7.9 102 57 30


75 71 75 75 70

401 94 92 3.9 7.7 11 402 91 91 3.1 6.4 11 403 90 89 3.8 7.1 12 404 85 83 3.2 7.8 11 405 85 84 4.2 9.0 11


411 65 67 5.4 13 11 412 61 63 5.9 15 10 413 73 78 8.0 17 12 414 61 62 5.7 12 10 415 65 69 7.3 6.0 11


411 65 70 5.4 70 37 23 76 412 64 67 5.1 66 40 22 71 413 75 83 7.3 93 55 29 67 414 62 67 5.3 68 41 22 69 415 68 73 6.1 79 46 24 66


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TABLE II-conduded.

R&No. j ;:;gy. ( $;$ 1 iEg. / in&& ( “p’ j yyy p:;$p


gm. om. gm. mo. ml. ml. per cent 411 69 66 2.7 6.1 12 412 64 64 2.9 6.7 12 413 81 81 4.5 9.2 11 414 66 65 3.1 8.4 8.6 415 74 72 3.3 6.3 9.8

absorbed nitrogen and represents the biological value of the cocoa nitrogen in this particular experiment.

Table III contains a summary of the coefficients of digestibility, corrected for the metabolic nitrogen in the feces, and of the biological values of the nitrogen of cocoa in fifteen individual experiments. Considerable variation will be seen to exist within

TABLE III. Digestibility and Biological Value of Nitrogen oj Cocoa.

Rat No.

331 332 333 334 335

341 342 343 344 345

361 362 363 364 365

Average. . . . . . . . . . .

-

.-

--

-

Digestibility. Biologid value.

38 22 35 34 41 33 38 26 41 35

37 41 46 66 63 65 33 47 35 38

42 40 30 38 12

44 17 27 24

38 37 -


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these two groups of figures, which is probably the result of two conditions. The cocoa rations were not particularly palatable to the experimental rats, and as a result the intake of food was too small to maintain constant weight, even though the energy intake appeared to be sufficient. In most cases, the rats lost

TABLE IV.

Digestibility and Biological Value of Nitrogen of a Mixture of Milk and Cocoa Containing Equal Parts of the Nitrc

Rat No. Digestibility. Biological value.

361 74 68 362 55 55 363 65 68 364 66 68 365 61 68

391 67 77 392 63 78 393 68 73 394 63 74 395 69 75

401 63 75 402 61 71 403 63 75 494 61 75 405 60 70

411 65 76 412 58 71 413 58 67 414 59 69 415 52 66

I I Average.............. 63

I 70

!n of Each.

weight continuously and appeared to be in a miserable condition at the end of the period. Concordant results cannot be expected with animals in a condition of marked malnutrition. In the second place, it is to be expected that the variation among individual determinations of digestibility and biological value will tend to increase as these values decrease. Given deviations


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in the amount of nitrogen apparently digested, or in the amount of nitrogen apparently retained in the body from the food in individual experiments, due either to faulty technique, inaccurate assumptions, or inherent biological variation, will have Dhe greater effect on the coefficients of digestibility and the biological values the smaller the amounts of absorbed nitrogen and retained nitrogen. The average coefficient of digestion of cocoa nitrogen in these fifteen tests is 38, while the average biological value of the digestible nitrogen is 37. These figures may perhaps be considered as fairly representative of cocoa when fed at a level of approximately 8 per cent of crude protein.

The protein value of a mixture of milk and cocoa containing the same amount of nitrogen from each was next investigated in metabolism experiments upon twenty rats. The results of this experiment relative to the coefficients of digestibility and the biological values are summarized in Table IV. This mixed ration was much more palatable to the rats than the ration of cocoa alone and was consumed in much larger amounts. Kever- theless it was evidently deficient in some essential constituent, since the amount of food consumed should have produced much larger gains in weight than were actually recorded. The results of the experiment are much less variable than those obtained with the cocoa alone and the averages may be considered as more sig- nificant. The average digestibility of this mixture of milk and cocoa nitrogen was 63 per cent and the average biological value, 70 per cent.

In one experiment on five rats the biological value of milk nitrogen alone was found to be 84. This value is practically identical with those previously reported (11). Assuming an average biological value for milk nitrogen and a digestibility of 100 per cent, it is possible to compute the digestibility and the biological value of a mixture of equal parts of milk and cocoa nitrogen, such as was fed in the second series of experiments, on the assumption than neither food influenced the utilization of the other. Taking the digestibility of cocoa nitrogen as 38 (see Table III), a mixture of equal parts of milk and cocoa nitrogen

would be expected to have a digestibility of 100 + 38 = 69 2

This value is not far from that actually obtained for such a mix-


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ture, namely 63 (see Table IV), and the approximation would be still closer if a digestibility of less than 100 is assumed for milk nitrogen. Assuming a digestibility of 95 would lower the estimated value to 66. These calculations, therefore, do not afford any basis for assuming any marked associative digestibility between these two foods.

TABLE V.

Daily Excretion of Creatine + Creatinine Nitrogen by Rats in Egg Ration Periods.

Initial period. I Final period.

Rat No. “i=?: weight.

- Per kilo >f body weight. i

ml.

21 21 21 21 22

-

-4bverdayge we:ght.

gm.

56 53 57 55 55

-

Total 1 er day. ,

As per cent of mine N.

Total KS day

As per cent of rim N.

331 332 333 334 335

gm. w.

63 1.31 61 1.30 61 1.28 62 1.28 59 1.28

7.6 7.5 7.9 7.2 7.5

mo. 1.36 1.32 1.30 1.30 1.34

-

‘er kilo )f body might. 1

_

mg.

24 25 23 24 24

12.5 8.9

12.0 10.1

9.6

341 64 1.45 23 6.7 59 1.47 25 8.7 342 61 1.39 23 7.0 55 1.42 26 10.2 343 62 1.48 24 7.6 55 1.49 27 10.6 344 63 1.58 25 7.8 54 1.52 28 9.7 345 65 1.44 22 7.3 58 1.47 25 12.5

361 78 362 70 363 90 364 73 365 83

1.34 1.31 1.62 1.32 1.56

-

17 7.4 19 8.2 18 8.1 18 8.7 19 7.8

84

104 83 90

1.25 15

14 15 15

10.1

1.51 1.29 1.35

9.6 12.2

9.4

Creatine + oreatinine N. Creatine + creatinine N.

-

In predicting the biological value of a mixture of cocoa and milk nitrogen in the ratio of 1 to 1, the marked difference in digestibility must be taken into account. Although the ratio of total nitrogen consumed was as 1 to 1, the ratio of digested nitrogen would be quite different, due to the low digestibility of the cocoa nitrogen. Again, assuming 100 per cent digestibility for milk and 38 for cocoa, the ratio of digestible milk nitrogen to digestible cocoa nitrogen would be 2.6 to 1. Weighting the average


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Protein Value of Cocoa and Chocolate

biological value (85) of milk nitrogen by 2.6 and that of cocoa nitrogen by 1, we obtain a biological value for the mixture of 72. This value is a remarkably close approximation to that actually obtained, namely 70, and again the approximation would be even closer if the digestibility of milk nitrogen were taken as less than 100. There is no reason to believe: therefore, that any supplementary relation exists between the digestible nitrogen of cocoa and that of milk. This finding is of considerable practical value in dietetics, since cocoa or chocolate is frequently consumed with milk either as a beverage or as a confection.

In most of the metabolism studies of this investigation the average daily excretion of total creatinine in the urine was deter- mined4 by a method described elsewhere (12). The results of this determination include the preformed creatinine as well as any creatine that might be present. A summary of the results for the egg ration periods, in which the nitrogen metabolism may be considered at the endogenous level, is given in Table V. The creatine coefficients of the rats in this experiment are quite similar to those previously reported from this laboratory and also to those computed from the data of Rose and Cook (13), relating to metabolism studies on twelve rats receiving a variety of diets, several of which were deficient in one or more indispensa- ble amino acids. These creatinine coefficients, for rats weighing from 70 to 200 gm., ranged from 17 to 25 and averaged 21. Morgan and Osburn (14) have reported creatinine coefficients of 13 to 14 for growing and adult rats, while Folin and Morris (15) found an average value of 15 mg. of creatinine nitrogen per kilo of body weight per day for adult rats and 10 mg. for young rats.

An unexpected result of the creatinine studies was the marked increase in the excretion of total creatinine in the urine for rats on the cocoa rations. This increase is shown by the summaries contained in Tables VI and VII. There was an increase of approximately 80 per cent in the excretion of creatine + creatinine nitrogen in the cocoa periods over the egg ration periods. The cocoa-milk ration also induced a large increase in creatinine excretion in marked contrast to the milk ration alone. While the

4 The creatinine determinations were made by Mr. R. L. Zimmerman.


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Mitchell, Beadles, and Keith

creatinine excretion was increased slightly on the milk ration as compared with the egg ration, the increase was almost exactly in proportion to the increase in body weight. These findings suggest the occurrence of creatine or creatinine or both in commercial cocoa powder.

TABLE VI.

E$ect of Ingestion of Cocoa on Daily Excretion of Creatine + Creatinine Nitrogen-by Rats.

-

--

-

Rat No. Em ration. Rat No. &E

ration. EfZS

ration.

I?7 1.42 1.49 1.52 1.47

COC7X3 ration.

w7.

2.51 2.58 2.58 2.47 2.60

Egg cocoa ration. ration.

w. w. w. 1.31 2.35 1.36 1.30 2.40 1.32 1.28 2.33 1.30 1.28 2.28 1.30 1.28 2.09 1.34

mg. 1.45 1.39 1.48 1.58 1.44

341 342 343 344 345

331 332 333 334 335

TABLE VII.

Daily Excretion of Creatine + Creatinine Nitrogen on Rations Containing, Respectively, Egg, Milk, and a Mixture of Milk and Cocoa.

Egg ration. Milk ration. Milk-cocoa ration. Egg ration.

Total exore- tion.

Rat No.

ml. ml. mg. mg. 1.34 17 1.58 16 1.31 19 1.50 18 1.62 18 1.82 18 1.32 18 1.63 18 1.56 19 1.79 19

%l. ml.

2.64 27 2.91 34 3.02 28 2.58 27 2.98 30

mg. ml.

1.25 15 361 362 363 364 365

1.51 1.29 1.35

14 15 15

A qualitative examination of the original cocoa powder used in the metabolism experiments indicated the presence of a water- soluble compound or compounds giving the Jaffe color reaction. Furthermore, the intensity of the reaction was perceptibly increased by boiling the water extract with picric acid previous to the addition of alkali. Carrying out the reaction in a quantitative way and expressing the results as creatinine gave a percentage of


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0.55 before boiling and 0.76 after boiling, both percentages refer- ring to the total weight of cocoa used. An attempt definitely to isolate and identify creatine or creatinine in cocoa is now being made.

SUMMARY.

When fed to young growing rats at a level of approximately 8 per cent crude protein, the nitrogen of cocoa was found to possess an average coefficient of digestibility (corrected for metabolic nitrogen in the feces) of 38. The average biological value of the absorbed nitrogen of cocoa was found to be 37, though the variation among the fifteen individual determinations was considerable.

The average true digestibility of a mixture of milk and cocoa nitrogen in the ratio of 1 to 1, also fed at a level of approximately 8 per cent crude protein, was found to be 63. Assuming the true digestibility of milk nitrogen to be 100 and that of cocoa nitrogen to be 38, the expected digestibility of a mixture of the two in equal amounts would be 69. If the digestibility of milk nitrogen is taken as 95 instead of 100, the estimate is reduced to 66.

An average biological value for milk nitrogen of 84 was obtained in metabolism studies on five rats. This is almost identical with the values previously reported.

For a mixture of milk and cocoa nitrogen in a proportion of 1 to 1, an average biological value of 70 was obtained. Assuming an average biological value of 85 for milk nitrogen, and making allowance for the great difference in the digestibility of milk and cocoa nitrogen, the estimated biological value of the cocoa nitrogen is 31. This indirect estimate of the biological value of cocoa nitrogen checks fairly well with that actually determined, i.e. 37, and the agreement would be closer if the digestibility of milk nitrogen were assumed to be less than 100. If a digestibility of 95 is assumed, the estimate for the biological value of cocoa nitrogen is raised to 40.

Such calculations may be considered both as a confirmation of the det,ermined biological value for cocoa nitrogen and as a strong indication that no marked supplementary relation exists between the nitrogenous compounds of milk and of cocoa, since, if such a


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relation existed, the estimated value for cocoa should be dis- tinctly higher than the determined value.

Cocoa, with an average crude protein content of 21.5 per cent, would, according to these investigations, contain 8.2 per cent of digestible crude protein, and only 3.0 per cent of “net” protein, available for replenishing and enlarging the protein content of the animal body. Evidently cocoa must be classed as an un- important protein food. The same conclusion applies with even greater force to chocolate, which contains a smaller percentage of crude protein than cocoa.

The ingestion of cocoa markedly increased the excretion of creatine + creatinine by rats, as determined by the reaction of Jaffe. An examination of the cocoa by this reaction indicated the presence in it of 0.55 per cent of creatinine and 0.24 per cent of creatine.

BIBLIOGRAPHY.

1. Whymper, R., Cocoa and chocolate: their chemistry and manufacture, Philadelphia, 2nd edition, 1921, chapter 1.

2. Stutzer, A., Z. Chem., 1891, 368. angew. 3. Forster, J., Hyg. Rundschau, 1900, 305. x, 4. Cf. Lancet, 1905, i, 47, 316. 5. Schlesinger, H., Deutsch. med. Woch., 1895, xxi, 80. 6. Cohn, H., Z. physiol. Chem., 1895, 1. xx, 7. Pincussohn, L., Z. klin. Med., 1907, lxiii, 450. 8. Neumann, R. O., Arch. Hyg., 1906, Iviii, 1. 9. Mitchell, H. H., J. Biol. Chem., 1923-24, lviii, 873. Mitchell, H. H.,

and Carman, G. G., J. Biol. Chem., 1924, lx, 613; 1926, lxviii, 183. 10. Osborne, T. B., and Mendel, L. B., .I. Biol. Chem., 1919, xxxvii, 557. 11. Mitchell, H. H., J. BioZ. Chem., 1923-24, lviii, 905. Mitchell, H. H.,

and Carman, G. G., J. BioZ. Chem., 1926, lxviii, 200. 12. Mitchell, H. H., and Carman, G. G., J. BioZ. Chem., 1926, lxviii, 211. 13. Rose, W. C., and Cook, K. G., J. BioZ. Chem., 1925, lxiv, 325. 14. Morgan, A. F., and Osburn, D. F., J. BioZ. Chem., 1925, Ixvi, 573. 15. Folin, O., and Morris, J. L., J. BioZ. Chem., 1913, xiv, 509.


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PROTEIN IN THE DIETCHOCOLATE AS SOURCES OF THE VALUE OF COCOA AND

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the value of cocoa and chocolate as sources of protein in the diet. the united

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