Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Nutrition, Dietetics, and Food Sciences

Department name when degree awarded

Nutrition and Food Sciences


Carol T. Windham


Genetically enhanced high-carotene Beta III hybrid carrot was compared to a commercial carrot cultivar, Nantes Careless, for carotene content and macronutrient composition. Beta III contained more than twice the total carotene content of Nantes Careless, with α-carotene/β-carotene ratios higher in Beta III. Total solids from protein, lipids, and carbohydrate were greater in Beta III than in Nantes Careless. Beta III contained about five times the amount of sucrose and one-fifth the amount of glucose and fructose than Nantes Careless or reported literature values.

Comparison of the bioavailability of carotenes in Beta III and Nantes Careless to purified β-carotene and retinyl acetate standards was made using two bioassays: the liver storage, slope-ratio assay and a curative growth study. Beta III provided liver retinol stores equivalent to stores provided by Nantes Careless, β-carotene, and retinyl acetate at dosage 300 RE. At 600 RE, only retinyl acetate increased liver retinol storage with dose. Carotene sources did not increase liver retinol storage, presumably owing to the mechanisms that prevent carotene vitamin A toxicity.

Growth study results indicated vitamin A potency of Beta III was not equivalent to that provided by retinyl acetate. Slopes of the growth response curves for Nantes Careless and β-carotene were not significantly different from retinyl acetate; the slope of the Beta III growth response curve was significantly different. All carotene sources were similar to retinyl acetate in the curvilinear response of the growth curves. The appropriate fit of the quadratic function to the growth response curves suggested 12 RE/d was greater than requirement.

The differences in results of the two bioassays used to determine bioavailability of carotenes in Beta III may be explained by a number of factors. The utilization of β-carotene from Beta III may be affected by a-carotene or other carrot constituents for absorption or conversion to vitamin A, or both. Stored liver retinol may be a combination of retinol and a-retinol with reduced vitamin A activity. The growth assay may be more sensitive to external variables that cannot be controlled.