Effects of thermal processing on the in vitro bioaccessibility and microstructure of beta-carotene in orange-fleshed sweet potato

The effects of different preparation methods on the bioaccessibility of beta-carotene in orange-fleshed sweet potato (OFSP), an important food crop in sub-Saharan Africa, have been evaluated using an in vitro digestion procedure. The preparation methods included, on fresh roots, boiling followed by pureeing and oil addition (BOL) and homogenization followed by boiling and oil addition (HOM); on milled flour from freeze-dried fresh roots, cooking of porridge followed by oil addition (POA) and oil addition to flour followed by cooking of porridge (POB). The retention of all-trans-beta-carotene ranged from 58% (POB) to 72% (BOL). The presence of oil during heating resulted in a significantly higher formation of 13-cis-beta-carotene for the POB-treated samples than for the other samples. The efficiency of micellarization of all-trans-beta-carotene after in vitro digestion was 50% (HOM), 48% (POB), 31% (POA), and 16% (BOL). Brightfield microscopy of the cell structure after processing and in vitro digestion showed a high degree of cell-wall rupture for the HOM-treated samples, whereas cells appeared intact for the BOL samples. Also, coherent anti-Stokes Raman scattering (CARS) microscopy showed smaller beta-carotene bodies residing in the HOM samples than in the BOL samples after digestion. These results suggest that the in vitro bioaccessibility of beta-carotene in an OFSP meal can be improved by processing methods that promote cell-wall rupture