Bowers, W. G.

Lyman, J. F.

The Ohio Journal of Science

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THE DIGESTIBILITY OF SOY BEAN MEAL BY MAN.*By J. F. LYMAN and W. G. BOWERS,There always has been considerable interest, in connectionwith human nutrition, in the seeds of the legumes. The commonwhite or navy bean has played a prominent part in the affairsof the United States in supplying nourishment to soldiers in theservice and to laborers on the farm and in the factory. Thebean has been recommended as the "poor man's beefsteak,"supplying as does meat, large quantities of proteins.In China and Japan another legume, the soy bean, is exten-sively used as human food. This is ordinarily prepared for thetable by processes not in general use in this country, usuallyinvolving some kind of fermentation. These preparations supplya very important part of the food requirement, especially of theprotein requirement, of the Chinese and Japanese, and havebeen found to be well utilized in the body, in some cases 96 percent of the protein being absorbed.1The soy bean has been cultivated rather extensively in theUnited States in recent years, but it has been used almostentirely as forage or for animal feed. Recently a soy beanmeal, a by-product in the manufacture of soy bean oil, hasbeen produced in considerable amounts in some sections of theSouth. The composition of this material and of the whole beansin comparison with common white beans suggests that we havehere valuable supplies of human food which should not beneglected. The following table gives the average composition ofthe different materials.2White beans (dry)...3Soy beansSoy bean mealMoisturePercent12.610.05'. 7ProteinPercent22.538.2946.66FatPercent1.814.895.1 ,FiberPercent4.44.645.5N-freeExtractPercent55.226.6432.3AshPercent3.55.545.75Obviously, chemical analyses alone do not measure thenutritive value of food. We must know also the digestibility ofthe food, the relative quality of its proteins, carbohydrates,fats and minerals, the extent to which accessory substances orvitamines occur, and finally whether, for any reason, it exerts aharmful influence on the body.* From the Laboratory of Agricultural Chemistry and Soils, The Ohio StateUniversity, Columbus.279280 The Ohio Journal of Science [Vol. XVIII, No. 7,Mendel and Fine4 found the- protein in mush prepared fromsoy beans to be from 74.5 to 87.6 per cent digestible by dogsand 85.3 per cent digestible by men (uncorrected values). Infact the protein of soy beans was only 2.6 per cent less digestiblethan was the protein in a mixed diet of wheat, meat, eggs andpeanut butter. The protein of the common white bean, bakedin the usual way, was distinctly less digestible, viz., 77.9 percent, in the human subject. The experiments of Wait5 on thedigestibility of white beans agree with this result. Daniels andNichols,6 from experiments on rats, have concluded that theproteins of the soy bean are highly efficient in promoting thegrowth of young animals, in fact, about as efficient as casein ofmilk. On the other hand, the proteins of the white bean appearto be decidedly poorer in quality or about as valuable as theproteins of corn.7 Osborne and Mendel8 found in soy beansabundant amounts of water-soluble accessory or vitamine, whilethe fat-soluble vitamine, though not abundant, appears toexceed the amount found in other seeds and grains commonlyused for human food.The nutritive quality of the white bean is further loweredby the presence of considerable amounts of carbohydrates,e. g,, hemicelluloses, which are indigestible in man, and whichferment in the intestine with the production of large quantitiesof gas, resulting in discomfort and even in injury to the intestinebecause of the stretching effect of the gas.7 The carbohydratesof the soy bean, while resembling those of the white bean, appearto be considerably more digestible and less prone to intestinalfermentation. Mendel and Fine4 in comparable experimentswith dogs, fed in one case soy bean flour and in the other apreparation made from hulled white beans, and found fivetimes as much fiber and over three times as much hemicellulosein the feces of the white bean fed animal. In the human subjectthe weight of the air dry feces from the soy bean feeding wasincreased only four per cent above the mixed diet period, whileon the white bean diet the increase in weight of air dry feceswas 68 per cent, indicating a good utilization of the non-nitrogenous material in the first case and a poor utilization inthe second. In our own experiments the liberal use of soy beanmeal in the diet, 120 grams per day for a three-day period, didnot result in voluminous stools, on the contrary, both the proteinand carbohydrates (N-free extract) of the soy bean meal washighly digestible, as will appear from the following experiment.May, 1918] Digestibility of Soy Bean Meal 281EXPERIMENT I.The subject was a healthy man, aged 38, weight 150 pounds,engaged in moderately active laboratory work each day. Since,obviously, it is impossible to consume with relish an exclusivediet of soy bean meal, a mixed diet was selected containing afew articles of known digestibility in addition to soy bean meal,the chief constituent. The feces from the three-day experi-mental period were marked off with lampblack taken with theappropriate meals. Soon after collection of the stools they weremoistened with alcohol containing a little sulphuric acid, driedon the steam bath, brought to an air-dry condition by exposureto the atmosphere of the laboratory and finely ground. Proteinwas determined by the Kjeldahl method (N x 6.25); fat by themethod of Gephart and Csonka,9 nitrogen-free extract, fiberand ash by the ordinary routine methods.10The soy bean meal used in this experiment had the followingcomposition:Moisture 6.5 percentAsh 5.7Protein 44.1 "Crude Fiber 5.9 "Fat 3.3N-free Extract 35.5 "Two hundred grams of this meal were mixed with 400grams of patent wheat flour and 10 grams of sugar and madeinto yeast-raised bread. This bread was of good texture andhighly palatable.The diet for the three days was as follows, approximatelyone-third being consumed each day.Grams ProteinGramsFatGramsN-freeExt.GramsCaloriesSoy bean meal ! 200Patent wheat flour 400Milk i 3000Butter ! 200Cane sugar 20088.253.2103.1Total. . . .Per Day.6.66.0120.0170.07128814120069614202064153080040001330244.581.5302.100.70023365102170282 The Ohio Journal of Science [Vol. XVIII, No. 7,The feces from the three days weighed 248 grams moist, and66.6 grams air-dry. They contained:Percent GramsMoisture 7.25 4.82Ash.. 19.70 13.12Protein 27.66 18.82Crude fiber 8.46 5.63Fat 22.01 14.65N-free extract 15.22 10.14In addition to undigested food residues, feces always containnitrogenous metabolic products derived (1) from the digestivefluids and (2) from mucous and epithelial cells from the walls ofthe digestive tract. In order to determine the amount of thesemetabolic products a basal ration consisting of milk, butter,sugar, starch and agar, and designed to yield feces of about thesame bulk as in the soy bean period was eaten. The diet wasas follows:3000 grams milk275 grains butter150 grams cane sugar130 grams potato starch, boiled in water to make a pudding.36 grams agar, eaten dry and raw.*One-third of the above was consumed daily for a three-dayperiod. The resulting feces weighed 270 grams moist, and 55.6grams air-dry, and contained:Percent GramsMoisture 5.36 2.98Ash 19.50 10.85Protein 11.90 6.60Fat , . . . 31.20 17.34Crude fiber 1.40 .77N-free extract. 30.60 17.03The protein in the feces of this period represents metabolicproducts from the digestive juices and intestinal walls as wellas some unabsorbed protein from the milk. Deducting thisfrom the protein eliminated in the feces during the soy beanperiod we have 18.82 — 6.60 = 12.22 grams, which represents theunabsorbed protein from the wheat flour and soy bean meal.This gives a coefficient of digestibility for the total protein ofthe bread of 91.3. Assuming that protein of patent wheat flouris 88.611 per cent digestible the coefficient of digestibility of thesoy bean meal pfotein becomes 93. This is hardly fair, however,since the coefficient 88.6 was obtained without making a cor-* The agar contained 6.35 percent of ash and 15.75 percent of moisture.May, 1918] Digestibility of Soy Bean Meal 283rection for metabolic products in the feces. We feel safe inconcluding, however, that soy bean meal prepared as in thisexperiment is as digestible as regards its protein as is the proteinof fine wheat flour which stands supreme among the cerealgrains in this respect.The carbohydrates of bread made from fine wheat flour are97.7 per cent absorbed in man,11 milk sugar 9912 per cent andcane sugar probably 100 per cent. Using these values thenitrogen-free extract of the soy bean meal is found to have acoefficient of digestibility of 96.9 per cent.EXPERIMENT II.In this experiment the soy bean meal was prepared as aporridge by cooking five hours in a double boiler. This sampleof meal contained more grit than that used in Experiment I,but not enough to increase the ash content greatly. It hadthe following composition:PercentMoisture 4.17Ash 5.80Protein 49.31Crude fiber 5.10Fat 6.50N-free extract 29.12The diet for the three-day period contained the following,approximately one-third being eaten each day:Milk.Butter..Cane sugarSoy bean mealTotalPer DayGrams20001503003702750917ProteinGrams7018225284FatGrams80.127.524.0231.577.2N-freeExtractGrams94300108502167Calories137611471200137550981699The fecal residue from this food weighed 224 grams moistand 58.1 grams air dry and contained:Percent GramsMoisture 4.40 2.56Ash 20.64 11.19Protein 39.90 23.20Crude fiber 7.00 4.06Fat 18.96 11.00N-free extract 9.00 5.22284 The Ohio Journal of Science [Vol. XVIII, No. 7,Assuming .that 6.06 grams of protein represents the unab-sorbed protein of the milk plus the metabolic protein from thedigestive fluids, etc., an assumption that can not be far fromthe truth, then the unabsorbed protein from the soy bean mealmust be 23.20 — 6.60 = 16.60 grams. This gives a coefficient ofdigestibility for the protein of the soy bean meal of 90.9. Ifthe carbohydrates of milk are 99 and cane sugar 100 per centabsorbed then the coefficient of digestibility for the nitrogen-free extract of the soy bean meal is 96. In this experiment, as inExperiment I, we cannot calculate accurately the digestibility ofthe fat but we were not particularly concerned with that phaseof the subject at this time. By adopting the proper experimentalprocedure one might determine satisfactorily the digestibilitycoefficient of soy bean fat, but for that purpose the amount ofthe experimental fat should be largely increased while other fatsin the diet should be reduced to a minimum.Summary: The protein of soy bean meal, prepared as abread by mixing with wheat flour or as a porridge, is highlydigestible by man. The digestibility factors obtained in thetwo experiments were 91.3 and 90.9.The carbohydrates of soy bean meal appear to be much morehighly digestible and less prone to intestinal fermentation thanare the carbohydrates of the common white bean. The digesti-bility factors obtained in two experiments were 96.9 and 96.The chemical composition, digestibility and palatability offoods prepared from soy bean meal from which most of the oilhas been expressed, indicate that such a meal is an excellentfood for man.REFERENCES.1. Oshima, Bui. 159 (1905), U. S. Dept. Agr. Office Exp. Stations.2. Bui. 28, U. S. Dept. Agr. Office Expt. Stations.3. Street and Bailey, J. Ind. Eng. Chem. 7, 853, (1915). -•.'••'•4. Mendel and Fine. J. Biol. Chem., 10, 447, (1914).5. Bull. 187, U. S. Dept. Agr. Office Expt. Stations.6. Daniels and Nichols, J. Biol. Chem., 32, 91, (1917).7. McCollum, Simmonds and Pitz; J. Biol. Chem., 29, 521, (1917),8. Osborne and Mendel, J. Biol. Chem., 32, 369, (1917).9. Gephart and Csonka, J. Biol. Chem., 19, 521, (1914).10. Bui. 107, U. S. Dept. Agr. Bureau Chem.11. Report Maine Expt. Station, 1898.12. Farmers Bui. 363, 22.Date of Publication, June 30,1918.

The Digestibility of Soy Bean Mean by Man

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The Digestibility of Soy Bean Mean by Man

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