Changes in microstructure, beta carotene content and in vitro bioaccessibility of orange-fleshed sweet potato roots stored under different conditions

Abstract

Orange-fleshed sweet potatoes {OFSP} (Ipomoea batatas (L.) Lam) contain high levels of beta carotene, an important provitamin A carotenoid. Stored sweet potato roots undergo many physiological changes that affect their beta carotene content and bioaccessibility as well as the tissue microstructure. This study investigated the changes in microstructure, beta carotene content and in vitro bioaccessibility of stored OFSP roots. Roots of two varieties of OFSP, Ejumula and SPK004/6/6 were each stored under the following conditions: in a pit (17-21 oC, RH 90-100%), saw dust (19-23oC, RH 86- 100%), dark room (24.5-28 oC, RH 68-100%) and ambient (24-27 oC, RH 68-100%). Samples were drawn monthly from each of the storage treatments and analyzed for changes in beta carotene content, in vitro bioaccessibility and tissue microstructure. Stored roots of Ejumula variety contained significantly more (P  0.05) beta carotene than those of the SPK004/6/6 variety. There was no significant difference (P  0.05) between varieties in regards to beta carotene bioaccessibility. Roots stored in pits retained higher beta carotene content compared to roots stored under other conditions. In vitro bioaccessibility was significantly higher (P  0.05) in roots stored in pits compared to roots stored under saw dust, dark room and ambient conditions. Samples of OFSP roots stored under ambient and dark room conditions retained the least amount of beta carotene and had the least amount of bioaccessible beta carotene. There was an increase in the level of cell wall lignification during storage of OFSP. The extent of lignification varied with storage method used. The roots stored under ambient and dark room conditions showed higher levels of lignification compared to those stored under sawdust and in pits. There were no differences in lignification between the different varieties studied. The study shows that storage of OFSP roots using methods that maintain low temperatures leads to higher retention of beta carotene and maintains higher in vitro bioaccessibility.

Key words: Storage, beta carotene, bioaccessibility, microstructure