Relation Between Vitamin A Potency and Carotene Content of Green Plant Tissue. ∗

Abstract

The finding that carotene is provitamin A for certain species-raises the question as to whether a direct determination of the carotene content of plant tissue, coupled with information with regard: to the vitamin A potency of isolated carotene, could be substituted for the extended biological assay. Euler, Demole, Karrer and Walker 1 report that a carotene determination in plant material discloses the magnitude of its vitamin A activity.

For the determination of carotene a colorimetric method was used, based on the original procedure of Willstatter and Stoll 2 but modified after critical study by one of us. 3 The vitamin A technique was essentially that employed by Sherman and has been referred to in an earlier publication. 4

Alfalfa samples 45, 46 and 49 were taken from adjacent parts of the same field. Nos. 45 and 46 were dried in a mechanical drier by artificial heat within a few hours after cutting and No. 49 was sun-dried in the field. Samples 61 and 62 were artificially-dried and sun-dried, respectively, but from different parts of the country. A stock solution of carotene from carrots was prepared by dissolving a weighed amount of the crystalline substance (M.P. 169-171°, corr.) in ethyl laurate and olive oil. A dilution was made with olive oil every 2 weeks and in order to insure a constant level of carotene intake a colorimetric determination was made before each dilution. Hydroquinone was added to all solutions to the extent of 1 mg. per cc. as an antioxidant.

Table 1 displays the feeding levels which are in a comparable range as to rat growth response.