Protein Nutritional Value Research Articles

Relationship of amino acids to the nutritive value of proteins

Relationship of amino acids to the nutritive value of proteins

EXPERIMENTAL FEEDING OF PROTEINS

To the Editor:— In the editorial on Nutritive Value of Proteins in the January 29 issue ofThe Journal, page 311, experiments are cited in which intact proteins were supplemented with a free amino acid (cysteine). At the American Medical Association Convention, in Atlantic City in June 1947, Dr. Paul Cannon described experiments on the utilization of a solution of a biologically adequate mixture of amino acids. When one of the essential amino acids was removed from the mixture and given one, two or four hours subsequent to administration of the balance of the mixture, utilization was impaired and negative nitrogen balance occurred. Dr. Cannon concluded that amino acids are available for utilization for not more than an hour or two after their introduction into the blood stream. An abstract (Kuiken, K. A., Lyman, C. M.: Availability of Amino Acids in Some Foods, J. Nutrition 36 : 359 [Sept.] 1948) which

Nutritive Value of Proteins Contained in Wheat Flours of Different Degrees of Extraction

Nutritive Value of Proteins Contained in Wheat Flours of Different Degrees of Extraction

Estimation of the Relative Nutritive Value of Vegetable Proteins by Two Chemical Methods

A comparison was made between gain in weight per unit of supplementary protein as determined by Draper and Evans (’44) on ten samples of commercial soybean oil meal, two of cottonseed meal, and two of cull peas, and the chemical protein quality index (Almquist, Stokstad, and Halbrook, ’35). A comparison between the gain in weight of chicks per unit of protein and the per cent protein present as albumin, globulin, prolamine, glutelin, and residual protein was also made. The chemical protein quality index appeared to give good indication of the relative protein nutritive value of the vegetable protein concentrates studied with the exception of the overcooked soybean oil meals. A coefficient of correlation between the gain per unit of supplementary protein and the chemical protein quality index of + 0.946 was obtained for all of the concentrates studied except the three expeller process soybean oil meals. A high coefficient of correlation of + 0.928 between the gain per unit of supplementary protein and the per cent glutelin was obtained for the heat treated concentrates. A determination of the per cent glutelin may offer a chemical means of estimating differences in the protein nutritive value of soybean oil meals and, in combination with the per cent residual protein, the extent of heat denaturation of the soybean proteins.

The Influence of Storage on the Supplementary Protein Nutritive Value of Certain Fish Meals

FISH meals have been demonstrated to be the most efficient protein concentrates for growing chicks (St. John, Carver, Johnson, Moore and Gerritz, 1933; St. John and Carver, 1936; Robertson, Carver and Cook, 1940). For that reason fish meals are very widely used in poultry feeding when available. Since the fishing industry is largely seasonal, most of the fish are caught and the fish meals prepared at one period during the year. Fish meals used during the remainder of the year must be stored until used. It appeared possible that some changes in the value of the fish meals as protein concentrates might take place during storage.Any changes in the nutritive value of fish meals during storage might be influenced by the type of fish meal, the method of preparation, the use of an antioxidant, or by the type of container in which the fish meal is stored. The experiment .

The Protein Nutritional Value of Soybean, Peanut, and Cottonseed Flours and Their Value as Supplements to Wheat Flour

The Protein Nutritional Value of Soybean, Peanut, and Cottonseed Flours and Their Value as Supplements to Wheat Flour

THE EFFECT OF HOT ALCOHOL ON PURIFIED ANIMAL PROTEINS

The effect of heat or alcohol extraction on the nutritive value of proteins continues to be an interesting problem. Most of the current work on it has been summarized in several recent papers (l-3). Heat treatment usually lowers the nutritive value, although soy bean protein seems to be modified in the opposite direction (4). In long time feeding experiments the possibility of thermal destruction of unidentified accessories had to be reckoned with but short time balance experiments have left no doubt that the protein itself is changed in a manner such that either it is less digestible or its amino acid fragments after digestion are less utilizable than is the case with the native protein. The latter view is the more generally accepted, although no chemical evidence has been offered which would indicate any alteration or destruction, especially of lysine or histidine, the amino acids held to be the first limiting nutritional factors in heat-treated proteins. Indeed, Block, Jones, and Gersdorff (5) found no difference between the lysine content of heated casein and that of the unheated. The work to be reported here had its origin in the observations of Seegers and Mattill (6) that beef liver, carefully dried at temperatures below 60”, suffered considerable loss of its value as a source of protein for growth and maintenance by being heated at 120” for 72 hours or by extraction with 95 per cent alcohol for 130 hours at the boiling point. When the two treated proteins and the untreated were hydrolyzed by acid, the resulting amino

219. The nutritive value of proteins for milk production. V. The effect of high temperature and of season on the nutritive value of grass proteins, the supplementary effect of the maintenance ration on the production ration, and the effect of feeding a high-protein ration

1. As regards the nutritive value of artificially dried spring grass, the protein appears to be unaffected by the temperature of drying even to the extent of scorching the grass. Early autumn dried grass has a biological value intermediate between spring and late autumn grass, while linseed cake has a very low value.2. The supplementary effect of the maintenance on the production ration has been shown when hay was substituted for straw in the maintenance ration together with a production protein intake of poor biological value.3. With an excess of protein in the ration most of the excess nitrogen was excreted in the urine, while both the milk yield and the biological value of the food protein fell considerably. It is possible that, together with an adequate amount of lysine in the protein ingested, a certain mixture of amino-acids is essential before maximum milk yield can be obtained.4. A study of the nitrogen metabolism shows that high-temperature drying has no effect, whereas marked effects were noted with the early autumn grass and more especially with the linseed cake. The hippuric acid nitrogen output decreased with the high-temperature dried grass, possibly the effect of a loss on drying of benzoic acid. With the high-protein diet an increased excretion of creatinine was noted with no alteration in the creatinine intake. The purin metabolism varies with the total nitrogen excretion, the allantoin increasing markedly in the high-protein period. This is due to an increased intake of purin base.5. The sulphur metabolism shows the results to be expected from previous publications except in the case of the high-temperature dried grass. It appears that the high-temperature treatment has in some way affected the nature of the sulphur compounds in the grass, with a consequent diminution in the retention.

111. The Nutritive Value of Proteins for Maintenance

The results of the present experiments may be summarised as follows:(1) When minimal quantities of protein are fed in the maintenance rationof steers, a deficiency of lysine will lead to a marked increase in the urinary N output. A deficiency of cystine has no effect.(2) The catabolism of body tissue is shown by the high creatine excretionand the S: N ratio of the excess S and N excreted. This is probably the resultof excessive deamination with the production of a mild acidosis.(3) As regards urinary partition of N there is some indication that alysine-deficient diet causes a decreased percentage excretion of urea N and anincrease of ammonia N.(4) The biological values have been calculated, the only marked difference occurring with wheat gluten, a protein very deficient in lysine(5) An approximate value for the lysine requirements for maintenance has been calculated, i.e. 0·80 g. lysine N per 1000 lb. live weight.

75. The Nutritive Value of Proteins for Milk Production. III. The Determination of the Amino Acids of Various Feeds

1. A modification of the method for estimation of the amino-acid content of foods is described.A series of analysis of the more important cattle foods is given.

67. The Nutritive Value of Proteins for Milk Production. II. A Comparison of the Proteins of Blood Meal, Pea Meal, Decorticated Earth-Nut Cake, and a Mixture of Decorticated Earth-Nut Cake and Flaked Maize

The results of the present experiments and of those reported in the previous paper(1) may be summarised as follows:1. When minimal quantities of protein are fed in the production rations of milking cows, a deficiency of either lysine or tryptophane will lead to a marked reduction in milk yield. There is, however, some evidence of the storage of reserve N, which can be utilised when the food protein is inadequate.2. The feeding of a lysine- or tryptophane-deficient ration causes a marked increase in urinary N, indicating a poor utilisation of food protein. On the other hand, the feeding of a ration containing adequate quantities of these essential amino acids reduces the urinary N, indicating efficient protein utilisation.3. The utilisation of body tissue in an attempt to maintain normal milk production on a deficient protein ration is shown by the high creatine excretion. The fact that the S: N ratio of the excess sulphur and nitrogen excreted during the deficient protein periods approximates that of body tissue (circa 1: 15·7) confirms this conclusion.

56. The Nutritive Value of Proteins for Milk Production. I. A Comparison of the Proteins of Beans, Linseed, and Meat Meal

The protein requirements for maintenance and milk production are based on the well-known investigations of Kellner, Armsby, Haecker, Savage and others, who recommend feeding standards varying from 0·5 to 0·;8 lb. digestible crude protein per 1000 lb. live weight for maintenance, and from 0·52 to 0·63 lb. digestible crude protein per 10 lb. milk for milk production. A detailed study of the work of these investigations shows that in many instances nitrogen equilibrium has been obtained on considerably lower planes of protein intake: but the figures have been arbitrarily raised, partly to provide a sufficient safeguard against underfeeding, and partly on the assumption that the excess food protein could exert a stimulating effect on mammary secretion. Recent investigations, particularly those of Hills and his associates (l), Perkins (2), Buschmann(3) and Savage and Harrison (4) indicate that the existing protein standards could, in fact, be considerably reduced. The above investigations have, however, been limited to a study of the quantity of protein required for maintenance and milk production, and no account has been taken of the possible effect of variations in the quality of proteins on their utilisation.

Nutritional Value of Proteins as Influenced by Exposure to Ultraviolet Irradiation.

Nutritional Value of Proteins as Influenced by Exposure to Ultraviolet Irradiation.

NUTRITION IN SCHOOLCHILDREN

It is not the purpose of this paper to discuss nutrition from the standpoint of calory requirement, relative protein nutritive value, vitamin content or metabolic processes. Our inquiry is directed more particularly to certain phases of nutrition work now being widely attempted in the schools, and which may affect, for better or for worse, 20 per cent. of the total population, representing the approximate school enrolment of a given community. For untold generations, men and women have been born, "had their being," and died at a ripe old age, without thought of the state of nutrition or the character of the food ingested other than that inspired by a catholic appetite. But, within the last few years, all has changed, and the popular conception of malnutrition is—shall I say?—so inaccurate that the veriest tyro in public health work, after placing a child on a scale and noting comparative results, gravely