In vitro bioaccessibility of beta-carotene in orange fleshed sweet potato (Ipomoea batatas, Lam.)

Abstract

Substitution of white with orange fleshed varieties of sweet potatoes (OFSP) was recently shown to alleviate vitamin A deficiency in children in Africa. However, the relationship between beta-carotene (BC) content of different cultivars of OFSP and its bioavailability is unknown. Here, we used the three phase (oral, gastric and small intestinal) in vitro digestion procedure to examine the bioaccessibility of BC from eight cultivars of boiled OFSP. All-trans BC (all-E-BC) was the only isomer of BC detected in raw roots for cultivars of OFSP with amounts ranging from 112 to 281 microg/g. Boiling OFSP decreased all-E-BC content by 11% with conversion to 13-cis BC (13-Z-BC). The efficiency of BC micellarization during simulated digestion of boiled OFSP was only 0.6-3%. Addition of soybean oil (2% vol/wt) to boiled OFSP prior to in vitro digestion more than doubled partitioning of all-E-BC in the micelle fraction for all cultivars. The relatively poor bioaccessibility of all-E-BC was not a limitation of the in vitro model as micellarization was proportional to amount of OFSP digested from 0.5 to 3.0 g and minimally altered by increasing bile salt content during small intestinal digestion. Moreover, micellarization of all-E-BC from boiled fresh OFSP and commercially processed OFSP was significantly less than from carrots processed identically. These results indicate the need for further efforts to elucidate the basis for relatively poor bioaccessibility of BC from OFSP.