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INDUSTRIAL A N D ENGINEERING CHEMISTRY
The Digestibility of Fats’
Vol. 15, S o . 3
*
By C. F. Langworthy OFFICEOF HOMEECONOMICS, STATESRELATIONS SERVICE, WASHINGTON, D. C.
tion was added. When. OTWITHSTANDBecause of the relation of fats to agriculture and their great imthis had reached its maxiI N G the fact that portance in the dfet, a long series of experiments on the thoroughness mum temperature (nearly fats and oils are an of digestion of animal and vegetable fats has been included in the important source of energy 100” C.), a mixture of cornstudies of food and its uses in the home. which were made in the in the diet and are two starch and the fat under Ofice of Home Economics. The work has been carried on at interand one-fourth times as consideration was slowly vals for seueralyears and has been reported in bulletins of the effective for this purpose added with constant stirU. S. Department of Agriculture and i n other publications.2 ring and the heating was as either proteins or carboThe studies have included twenty-three animal fats. thirty-four continued until the starch hydrates, their dietetic use vegetable fats. and six hydrogenated oils. In all cases the goods seemed well cooked. The has received less attention were bought in the open market or specially prepared either in the a t the hands of investigacaramel solution gave the Department of Agriculture laboratories or in some other way which pudding a slightly bitter tors than other food constitassured full knowledge . . - of . the process. uents, and is consequently taste, but this could be less well understood. readily overcome by addThe general assumption has been that when eaten in ing a little vanilla extract when the pudding had cooled. favorable combinations fats are well assimilated and that The cornstarch pudding prepared in this way resembles a they do not vary enough in this respect to affect materially common household dessert except that it is not noticeably the amount of energy which the body receives from them. sweet. By this method it is possible to mask t o a large exExperimental data are limited also with respect to the re- tent the texture and flavor of the fats and oils. The good lation of melting point to thoroughness of digestion, par- results obtained in this laboratory with this cornstarch ticularly in the case of fats with a high melting point. This mixture as a medium for supplying fat and other special is a matter of particular interest, since increased demand for foodstuffs to the diet indicate that it might prove valuable culinary and table fats tends to bring into the market kinds in invalid dietetics, particularly where a patient has an averwhich hitherto have been used little, if at all. sion to a large amount of fat or other foodstuff. The cornstarch mixture was used for all the fats and oils PREPARATION OF TESTMEALS here considered except fish and avocado fat. In these two Since it was rarely possible to find a subject who could cases the fat was not separated out. The fish meat, fat and eat fats and oils in quantity in their natural state, a method lean together, was freed from bone and made up into fish of preparing them was sought which did not submit the loaf, such as had been successfully used in previous similar fats to high temperature for any considerable time, was experiments in this laboratory. The fresh avocado pulp applicable to the different kinds of fat, gave a reasonably was fed simply with a little salt or lemon juice, as is a common palatable dish, and could be prepared in quantity sufficient custom. Experience has shown that in such digestion experiments for the entire experimental period. A method which proved satisfactory was to incorporate the fats in a sweet cornstarch a simple mixed diet is more pleasing to the subject than a pudding or blanc-mange. This was prepared by cooking single food; consequently, in this work with fats the cornin an ordinary double boiler a mixture of skim milk and sugar starch pudding was supplemented with a very simple basal to which a considerable quantity of very dark caramel solu- diet consisting of a commercial wheat biscuit or cracker, some fruit, and tea or coffee with a little sugar if the subject 1 Presented before the Division of Food Chemistry a t the 64th Meeting desired it. of the American Chemical Society, Pittsburgh, Pa., September 4 t o 8, 1922.
N
2 “Digestibility of Some Animal Fats,” U . S. Dept. Agr., Bull. 310, (Beef f a t , butter, lard, mutton fat.) “Digestibility of Some Vegetable Fats,” U . S. Dept. Agr., Bull. 605. (Cocoa butter, coconut oil, cottonseed oil, olive oil, peanut oil, sesame oil.) “Studies on the Digestibility of Some Animal Fats,” U.S.Depl. A g r . , Bull. 607. (Brisket fat, chicken fat, cream, egg-yolk fat, fish fat, goose fat.) “Digestibility, of Certain Miscellaneous Animal Fats,” U . S. Dept. A g r . , Bull. 613. (Goat’s butter, hard-palate fat, horse fat, kid fat, oleo oil, oleostearin, ox-marrow fat, ox-tail fat, turtle fat.) “Studies on the Digestibility of Some N u t Oils,” U. S. D e p l . Agr., Bull. 630.’ (Almond oil, black-walnut oil, English-walnut oil, Brazil-nut oil, butternut oil, hickory-nut oil, pecan oil.) “Digestibility of Some Seed Oils,” U . S. Dept. Agr., Bull. 687. (Corn oil, soy-bean oil, sunflower-seed oil, Japanese mustard-seed oil, rapeseed oil, charlock oil.) “Digestibility of Some By-product Oils,” U.S.Dept. Agv., Bull. 781. (Apricot-kernel oil, cherry-kernel oil, melon-seed oil, peach-kernel oil, pumpkin-seed oil, tomato-seed oil.) “Digestibility of Cod-Liver, Java Almond, Tea-Seed, and WatermelonSeed Oils, Deer F a t , and Some Blended Hydrogenated Fats,” U . S. Dept. Agr., Bull. 1033. “Digestibility of Certain Miscellaneous Vegetable Fats,” J . B i d . Chem., 1920,227. (Avocado fat, cohune oil, cupuassu fat, hempseed oil, palm-kernel oil, poppy-seed oil.) “Digestibility of Some Hydrogenated Oils,” A m . J. Physiol., 54 (1921),
479.
PROCEDURE A survey of the literature clearly shows that some variation in results can be expected in digestion experiments with different procedures, the analytical methods followed having some effect, for instance, on the determination of the quantity of fat extracted. There is also some difference of opinion regarding the desirable length of digestion periods and the methods of separating the feces; therefore the results of digestion experiments will vary within limits according to these differences in methods. However, from the extended experience, covering some twenty-five years or more, in which such problems have been studied in connection with the Department of Agriculture’s food work, it is fair to conclude that where the same experimental procedure is followed, the results with various food materials are directly comparable. The method developed and followed in this laboratory is one of several, the value of which is generally recognized, No method yet devised is absolute. Our experience, however, leads us to believe that any of these methods consistently followed throughout a series of experiments will yield re-
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March, 1923
liable results and that the range of variations between individual tests with the same kinds of material will be similar whatever the method. I n order to give comparable results, however, any method must be applied in essentially the same way in every case. TABLEI-DIGESTIBILITYOF ANIMALFATS -DIGESTIBILITY----
FATUSEDIN TEST
Melting Point C. 32
No. of Tests 8 7 4 9 10 7
Butter fat Cream Goat's butter 35 Lard Beef suet (rendered) 45 Beef brisket .. Hard-palate fat of cattle 34 Ox-marrow fat Ox-tail fat 36.8 Mutton suet (rend.) 50 Kid fat .. Horse fat: Deer fat 49154 Chicken fat .. Goose fat .. Oleo oil .. Oleostearin .. Egg-yolk fat Fish fat Room temp. Turtle fat .. Cod-liver oil Room temp.
..
..
3 4 3 7 3 3 3 8 7 8 3 6 3 4 4
Highest Lowest Per Per cent cent 95.7 90.9 95.2 89.3 94.8 92.4 95.7 88.2 94.4 82.4 95.9 89.1
91.7 93.3 95.0 88.2 95.2 95.0 75.4 95.3 96.5 92.5 79.0 92.1 96.2 94.5 93.8
88.8 89.3 89.0 72.4 87.7 92.4 71.5 92.0 91.6 87.4 66.4 90.9 94.2 91.8 88.9
Av. Per cent 93.9 92.7 93.6 93.7 88.9 92.8
90.5 91.2 93.0 80.5 91.3 93.6 73.9 93.4 94.2 90.4 71.8 91.5 95.4 93.3 92.6
Corrected for Metabolic Products and Fat of Basal Ration Per cent 97.0 96.9 98.4 97.0 93.0 97.4
93.7 93.5 96.6 88.0 95.3 93.9 81.7 96.7 95.2 96.8 80.1 93.8 96.1 98.6 97.7
In the work under consideration the experimental period covers three days. The feces are marked for separation with charcoal or carmine, or both supplied with the first meal of the experimental period and the first meal after it. The feces for the entire period are dried, thoroughly mixed, and sampled, and analyzed by the standardized methods of the Association of Official Agricultural Chemists. I n calculating the results, corrections are made for the small amount of fat introduced in the skim milk used in the blancmange and in the basal ration, and also for metabolic products in the feces, the factors used being based on what is believed to be ample experimental evidence. Uniformity is also observed in the choice of subjects. Generally speaking, they TABLE11-DIGESTIBILITYOF SOMEVEGETABLE FATS -DIGESTIBILITYCorrected for Metabolic Products and Fat of Melting Highest Lowest Av. Basal No. of Per Per Per Ration Point FATUSEDIN TEST C. Tests cent cent cent Percent 10 95.6 91.5 94.7 97.8 Olive oil 12 96.9 91.6 94.9 97.6 Cottonseed oil 7 94.9 88.6 93.5 96.9 Corn oil 5 96.3 92.1 93.8 98.0 Sesame oil 7 95.8 92.4 93.8 97.5 Soy-bean oil 96.5 Sunflower-seed oil Room temp. 4 '95.2 91.9 93.8 Japanese mustardseed oil . 3 96.6 92.6 94.9 95.8 Rapeseed oil 4 96.6 93.7 95.7 98.8 Charlock (wild mustard) seed ail 4 96.3 93.7 94.6 98.9 Cocoa butter 11 95.5 79.1 89.6 94.9 30 Peanut oil 5 97.6 93.7 96.0 98.3 Coconut oil 12 96.3 88.1 93.5 97.9 Almond oil 4 96.2 86.3 93.1 97.1 Black-walnut oil 4 96.7 91.9 94.8 97.5 Brazil-nut oil 3 96.8 92.8 94.5 96.3 Butternut oil 3 94.7 85.3 88.7 95.4 English-walnut oil 3 95.6 92.5 94.4 97.6 Hickorynut oil 4 98.4 96.5 97.2 99.3 Pecan oil 4 96.9 90.1 93.9 96.8 Apricot-kernel oil Roomtemp. 4 96.4 92.3 94.4 98.4 Cherry-kernel oil 4 95.5 93.0 95.2 98.0 Peach-kernel oil 3 96.5 87.0 91.6 96.6 Watermelon-seed oil 3 94.2 88.5 90.7 94.8 Melon- (cantaloupe) seed oil 3 97.7 92.1 94.8 98.2 Pumpkin-seed oil 2 95.0 94.9 95.0 98.2 Tomato-seed oil 3 91.3 88.1 90.3 95.8 Palm-kernel oil 4 97.5 93.9 95.3 98.0 Hempseed oil 3 94.7 94.0 94.4 98.5 Poppy-seed oil 7 93.4 87.4 91.3 96.3 Cohune oil Near 28 4 94.7 94.0 94.6 99.1 Cupuassu fat 4 91.0 86.3 88.8 94.1 Avocado fat 3 90.8 88.7 90.0 87.9 ava-almond oil Roomtemp. 2 95.5 89.0 92.2 97.0 &ea-seed oil 1 88.2 91.2
1
.. ..
.... ....
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have been laboratory assistants or students of local medical or dental schools who had an intelligent interest in the work, which was a decided help in conducting the experiments. I n a general way the subjects had more or less knowledge of the problems studied, but they were not given any definite information regarding the special foods under consideration.
RESULTS I n summing up the results it has seemed desirable to group the fats according to their origin, and the tables which follow show the coefficients of digestibility of animal fats in Table I, of vegetable fats in Table 11, and of oils hydrogenated to a definite point in comparison with a blend obtained by mixing a softer fat with one hydrogenated to a high melting point in Table 111. TABLE 111-DIGESTIBILITYO F HYDROGENATED FATS c DIGESTIBILITY----. Corrected for Metabolic Products and Fat of Melting Highest Lowest Av. Basal Point No. of Per Per Per Ration FATUSEDI N TSST O C . Tests cent cent cent Percent Oils Hydrogenated t o Definite Melting Points 33.0 95.0 87.6 91.7 Hydrogenated corn ail 94.7 42.0 93.8 89.4 91.8 95.4 50.0 91.2 78.9 82.2 88.5 35.0 96.9 89.7 93.6 Hydrogenated cottonseed oil 96.8 92.7 92.7 95.5 38.6 46.0 93.8 91.0 92.7 94.9 37.0 96.9 94.0 95.0 98.1 Hydrogenated peanut oil 39.0 95.4 90.2 93.3 95.9 43.0 5 96.9 90.1 93.5 96.5 50.0 4 90.3 86.6 88.1 92.0 52.4 3 81.8 65.8 73.8 79.0 Hvdroaenated Oils Blended to De5nile Mettinn Points - 94.9 88.5 92.1 95.2 Blended hydrogenated corn oil 39.0 4 49.0 3 92.4 87.0 80.4 93.3 90.1 83.5 87.8 54.0 3 91.5 92.8 91.9 92.4 96.6 Blended hydrogenated cotton- 41.3 2 93.8 90.5 92.2 96.4 seed oil 45.8 2 94.0 85.4 90.7 94.2 47.8 4 90.2 89.5 89.8 94.4 48.1 2 85.6 76.3 82.0 87.0 50.0 3 94.2 91.5 92.7 96.6 Blended hydrogenated peanut 43.0 3 97.0 91.3 94.4 97.4 oil 44.2 4 91.8 87.2 89.8 92.8 51.1 4
....
Consideration of the figures shows that ordinarily there are no very great differences in the digestibility of the fats studied. The animal and vegetable fats and the oils liquid at ordinary room temperature, for instance, have very much the same digestibility. It is apparent, however, that fats and oils melting above the body temperature are not quite so thoroughly assimilated, and the observed data seem to warrant the conclusion that the thoroughness of digestion is inversely proportional to the melting point. Experiments with the hydrogenated fats indicate that fats hydrogenated to a definite melting point and those made by mixing a softer fat with one hydrogenated to a much higher melting point do not differ essentially in thoroughness of digestion. It was very noticeable in this extended series of digestion experiments and in similar series with other foods that the diet did not become monotonous arid that the regularity in the diet and all that pertained to it was not irksome or disturbing. The amount of fat eaten per person per day varied within considerable limits, 50 to 60 g. being regarded as a small quantity per day, and 110 or 115 g. as a generous amount. Seldom, if ever, was any physiological disturbance noted when smaller amounts were eaten, nor was any observed in the majority of cases when the larger amounts were taken. However, it seems clear that in some cases, because of the nature of the fats themselves or because of unidentified substances accompanying them, they exercised a more or less laxative effect.' For instance, this effect was observed when 140 g. of rendered beef suet were eaten per day, and was not noticeable with butter, lard, or mutton fat used in the same series of tests. In the case of olive oil and most
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of the other oils used, as much as 116 to 130 g. were eaten per day with no laxative effect. I n the case of cocoa butter, however, a decidedly laxative effect accompanied by slight nausea was noted, indicating that the limit of tolerance of this fat is not so high as that of the other oils. A similar effect was also noted with cupuassu fat, which comes from a tree rather closely related to the theobroma cocoa. It is also worth mentioning that a laxative effect was noted when goose fat was eaten in quantity but was not noted with a comparable amount of chicken fat. It seems not unlikely that studies undertaken t o explain these observed divergencies would yield very interesting results. CONCLUSION From the investigations as a whole it seems fair to conclude that fats are wholesome, useful foodstuffs, which are well assimilated, and that for such reasons they deserve the im-
Vol. 15, No. 3
portant place they have in the diet. The fact that they are often carriers of vitamins is another reason for the esteem in which they are held. No attempt can be made here to discuss their effect upon palatability of the diet and their important relation to the texture, flavor, and quality of the foods into which they enter, though these and other matters relating to fats are being studied in the Office of Home Economics, where it is also proposed to continue the work on the digestibility of fats when new ones or new processes of manufacture add to the list of material available for such purposes. ACKNOWLEDGMENT No account of this work carried on in the Office of Home Economics would be complete without noting the fact that much of its success is due to Mr. Arthur D. Holmes and Mr. Harry J. Deuel, who assumed direct charge of the experiments.
Fats in t h e Evaporated Milk Industry’ Certain Physical and Chemical Requirements By Harper F. Zoller NIZERLABORATORIES C O . , D E T R O ~ MICH. T,
T
HE ICE-CREAM and cheese industries generally have a large surplus of skim milk to dispose of during certain seasons of the year. For the last few years a certain amount of this skim milk has been turned into sweetened condensed skim milk, which is sold to the baking industry and some to the candy manufacturers. Attempts have been made to put up the skim milk as straight evaporated skim in gallon cans for the candy trade, etc., but owing t o certain properties possessed by skim milk, it is necessary to run the total solids very low (around 20 per cent) in order that it will stand up under sterilization treatment. Certain companies have, therefore, conceived the idea of adding to this skim milk a fat from some suitable source, so that its total solids can be run to around normal content for evaporated whole milk (28 per cent) and still withstand sterilization. The addition of this fat was welcomed by the candy and baking industries, as it was thus a suitable cooking product in the place of whole evaporated milk. This fat-filled skim milk has earned the name in trade of “filled milk” or “milk compound.” So valuable has it become to the household in certain localities that it is canned in regular size evaporated-milk containers and is retailed as “milk compound” at many grocery stores a t a price of two to three cents less per tall can of product. Without entering upon a discussion of the commercial ethics of such a product-such discussions have engrossed the attention of certain factions in both state and federa1 government during the past few months-certain very fundamental research problems which have been uncovered by the manufacturers and laboratories connected with the production of compound milk will be described. The aim of the producers of the product has always been to secure a highly refined oil and to incorporate it under the most sanitary condition possible. I n many instances the character and physical conditibn of this fat-filled milk have been much superior to some whole-milk batches in its working conditions in the vacuum pan and in subsequent sthrilization. 1 Presented before the Division of Agricultural and Food Chemistry at the 64th Meeting of the American Chemical Society, Pittsburgh, Pa., September 4 to 8, 1922.
PROCESSING OF FATSI N
THE
COMPOUND MILK IKDUSTRY
The evaporation of milk in a vacuum pan a t the temperature and pressure under factory operation, and the subsequent sterilization of the product a t high temperatures, necessitates the consideration of factors in connection with the constitution and physical make-up of fats, which are uncommon in all other industries in which fats are used. We might say that those who were pioneers in the compoundmilk industry were the unquestionable recipients of luck in the choice of fats for their purpose. I n England and Denmark where the nut-margarine industry first flourished, and subsequently in the United States, coconut fat and palmnut fat were, and are yet, extensively used to manufacture their product. These two fats are reasonably cheap and are easily refined. The coconut oil is imported into the United States markets from our insular possessions. Inasmuch as the margarine people were using tons of this oil annually in the production of their product, it was but natural that the evaporated-milk people should look to this fat as the first possibility for compound milk. It filled the bill admirably. Just why it bhould be SO valuable for the evaporated filled-milk industry will be seen in that which follows, It is fitting that we should turn first to the properties of butter fat to ascertain the factors that render it capable of standing up fairly well during the evaporation in the vacuum pan and during sterilization. An authorative table of its properties is compiled beJow9 TABLB 1 FACTOR Melting point C.......................... Solidifying point ............................ Saponification, lbs.. ......................... Iodine Ibs .................................. Specifik gravity ............................. Refractive index.. ........................... Acetyl, lbs.. ................................
RANGE 28-36 19-24 220-241 26-38 0.86E-0.870 1.4527-1.4566 1.9-8.4
Comparison figures of the various fats suitable and those which are not suitable for evaporated milk as they exiat naturally, appear in Table 11. 2 Leach and Winton’s “Food Analysis,” 1920, p. 486; Allen’s “Commercial Organic Analysis,” 2 (1910),1.
