A study of the biological utilization of carotenoids of carrot and swamp cabbage in rats

The biological utilization of carotenoids is related to their provitamin A activity and the efficiency of their absorption and conversion to retinol and also their function as antioxidants. For practical purposes, various authorities have taken the efficiency of conversion of β-carotene to retinol to be in the ratio of 6:1, and that of other provitamin A carotenoids as 12:1. This paper presents results of a study carried out to determine the bioavailability of carotenoids present in two carotenoid-rich vegetables (namely carrot and swamp cabbage, kangkong) and aims to provide further information on the nutritional value of these important sources of provitamin A compounds. The growth and the levels of retinol and carotenoids in the liver and serum of rats provided with these carotenoids in the daily diet were monitored. These results were compared with the biological utilization of crystalline retinol and β-carotene concentrates. Two different experimental procedures were adopted for the study, namely supplementation and depletion-repletion procedures using the rat as the test animal. Both procedures showed that the bioavailability of the major carotenoids in carrot (α- and β-carotene) and kangkong (β-carotene) was high, as evidenced by the accumulation of retinol in the liver of the experimental rats, in relation to crystalline retinol concentrate. The provitamin A activity of α- and β-carotenes in the vegetables approximates the commonly used factors of 112 and 16 that of retinol, respectively. Either one of the experimental procedures may be used for the study of bioavailability of carotenoids in plant sources. The supplementation procedure, however, takes a shorter time to carry out and could be advantageous. The 4-week supplementation period was quite sufficient to obtain clearly observable differences. To further reduce time and cost of analysis, a 2-week supplementation would suffice, and liver retinol and carotenoid concentrations could be determined before and after supplementation. Such studies on the bioavailability of carotenoids should be extended to human subjects.