Protein Hydrolysates

Commercial products commonly referred to as protein hydrolysates are now available. They are prepared by hydrolyzing proteins with acids or by digestion with enzymes. They are, in fact, predigested proteins and consist chiefly of amino acids. These products have been found valuable for supplying amino acids for the use of patients who cannot take ordinary food in the normal way. Protein hydrolysates are used orally in a dry form or in solutions carefully prepared for parenteral administration.

Preparations for oral use are on the market under several trade names. They may be used directly or in cereals, sandwich spreads, milk, and other foods. Their use makes possible, when needed, a much greater intake of amino acids than can be supplied by the daily amount of protein food in the regular diet.

Parenteral injection of solutions of protein hydrolysates is of great value in cases of shock, extreme weakness, starvation, extensive losses of body nitrogen resulting from severe burns, and extensive loss of blood. There seems to be little advantage, however, in using protein hydrolysates for normally healthy persons, because the proteins in the diet are digested in the alimentary tract and yield the same amino acids as the hydrolysates supply.

Supplementary Relationships of Proteins

Several important foods contain proteins that are deficient in one or more of the nutritionally essential amino acids. When one of these foods constitutes the only source of protein in the diet, malnutrition ion inevitably results. It does not follow, however, that such foods may not have an important place in the diet as a source of protein, but they should not be relied upon as its only source.

When supplemented by certain other protein foods, even in relatively small proportions, they can satisfactorily constitute a large proportion of the daily protein requirement. The following are well known examples of some proteins of important foods that are deficient or lacking in one or more of the essential amino acids. Gliadin, one of the two chief proteins of wheat, is deficient in lysine. Zein of corn contains no tryptophane, and it is low in lysine. Phaseolin, of the common white navy bean, requires the addition of methionine or cystine in order to make it adequate to support satisfactory growth in young animals. Gelatine, a classic example of an incomplete protein, is deficient in valine, isoleucine, histidine, and other amino acids. Young animals fed deficient proteins as the only source of it will not grow unless the missing amino acids are supplied.

But most of the naturally occurring protein foods contain more than one kind of protein, each of which may have a different assortment of amino acids occurring in varying proportions. An amino acid deficiency in any one of the proteins may, therefore, be largely or entirely compensated by the other proteins present. Wheat, for instance, contains other Proteins than gliadin, namely gluten and the proteins of the bran and germ. These proteins largely compensate for the amino acid deficiency Of gliadin. Similarly, the low content of lysine and tryptophane in the zein of corn is corrected to a large extent by the other proteins present in the seed. Conarachin in the peanut supplies methionine, a small amount of which is contained in arachin.

The proteins of soybean, peanut, and cottonseed flours are excellent supplements for correcting the amino acid deficiencies of patent wheat flour. Mixtures produced by adding as little as 5 parts of soybean, peanut, or cottonseed flours to 95 parts of wheat flour contain 16 to 19 percent more protein than the wheat flour alone, and have a definitely greater growth-promoting value of the protein.

When mixed with wheat flour in the proportions of 5 to 95 parts, soybean flour has a higher supplementary value than peanut or cottonseed flour, but is inferior to that of skim-milk powder. In a mixture of 10 parts of the supplement and 90 parts of wheat flour, soybean flour has practically the same supplementary value as skim-milk powder; animals grow four times faster on it than on wheat flour alone. A mixture consisting of 15 parts of soybean flour and 85 parts of wheat flour has been found to have a nutritional value exceeding that obtained with a mixture of skim-milk powder and wheat flour in the same proportions.

Available data leave little doubt that the relatively high lysine content of the oilseed proteins is the amino acid that is outstandingly effective in making up for its deficiency in wheat flour. The oilseeds also contain relatively larger proportions of valine and tryptophane than wheat flour.

When they are supplemented with small proportions of the oilseed proteins, the cereal grains could be utilized as an important source of nutritionally adequate protein at a relatively low cost.