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Journal of Nutrition Vol. 12 No. 3 September 1936, pp. 237-254
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The Availability of the Proteins and Inorganic Salts of the Green Leaf

One Figure

M. K. Horwitt1, G. R. Cowgill and L. B. Mendel2

Department of Physiological Chemistry, Yale University, New Haven, Connecticut

A study of the known in vitro digestion technics failed to produce a practical method that might be used to determine the utilizable nitrogen in the green leaf. The results obtained, however, suggested that a closer approximation to the available nitrogen could be obtained by eliminating the fat soluble nitrogen, by means of extraction with an alcohol-ether mixture, and by boiling off the nitrate, ammonia and amide nitrogen from the substance to be analyzed before determining protein and amino acid nitrogen. On this basis a simple procedure for estimating the available nitrogen present has been devised.

An investigation of the digestion of spinach by successive treatment with pepsin, trypsin and erepsin was made. The results obtained when the entire leaf was digested are similar to those obtained with pure proteins. This indicates that with certain materials, at least, it is possible to perform exact proteolytic digestions without necessarily isolating the protein.

The application of in vitro digestions to determine the availabilities of the calcium, iron, chloride and phosphorus in spinach confirmed the view advanced in the literature that the calcium and iron in spinach is only partly available. Enzymatic digestion brought about 30% of the calcium and 40% of the iron into solution. Chloride and phosphorus were readily dissolved in water alone.

1 The data in this paper were taken from a dissertation presented by M. K. Horwitt in partial fulfillment of the requirements for the degree of doctor of philosophy, Yale University, 1935. Lack of space prevents the presentation of more detailed data than are reported here. Additional details are in the dissertation deposited in the Yale University Library.

A preliminary report of this material was presented before the American Institute of Nutrition, Washington, D. C., on March 25, 1936.

2 Deceased December 9, 1935.

Manuscript received 28 May 1936.




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