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Comparison of Chemical Analysis and Bioassay as Measures of Vitamin A Value of Some Vegetables and the Effect of Comminution upon the Bioassay Value

Bureau of Human Nutrition and Home Economics, Agricultural Research Administration, United States Department of Agriculture, Washington, D. C.

Chemical measurements of the biologically active carotenoids of the two principal yellow root vegetables, carrots and sweet potatoes, were compared with the biological vitamin A value obtained by rat growth bioassay of as nearly identical a sample of the vegetable as possible. In addition, study was made of the effect upon the availability of carotene to the animal of comminution of the vegetable and of extraction of carotene from the vegetable matrix. The carrots were of the Imperator and the sweet potatoes of the Porto Rico variety, and both were cooked before analysis.

The carrots averaged 26 µg of -carotene and 65 µg of ß-carotene per gram of cooked vegetable; the biological vitamin A value was 34% of that calculated from the carotene content when the carrots fed were sliced, and 41% when they were pureed. The sweet potatoes averaged 44 µg of ß-carotene per gram cooked vegetable and bioassay gave 37% of this value regardless of whether the sweet potato was sliced or mashed. The percentage availability of carotene from these yellow root vegetables is contrasted with 67% for cooked kale, reported earlier from this laboratory.

The feasibility is indicated of obtaining a factor for each vegetable, or possibly each class of carotene-bearing plant foods (yellow or red fruit, yellow root, green leafy, green leguminous vegetables), which could be used to convert provitamin A content in terms of carotene to the equivalent international vitamin A units, derived biologically, or vice versa. A conversion of this nature is necessary in order either to combine or to compare with any degree of validity vitamin A values obtained by the two methods.

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