In vitro Bioaccessibility of Carotenes: Influence of microstructure in tomato and carrot as modified by processing

Doctoral thesis, 2011

Carotenes are a group of fat-soluble pigments in many fruits and vegetables associated with several important biological effects, like protection against the development of some forms of cancer and cardiovascular disease. The carotene bioavailability in plant foods, i.e. the fraction of ingested carotenes taken up and utilised in the body, is often increased by processing. The increased bioavailability is often ascribed to changes in the microstructure, but few studies have investigated this in detail. The aim of the present work was to evaluate how different types of thermal and mechanical processing, and addition of dietary fat, affected the bioaccessibility of the carotenes lycopene, α-carotene and β-carotene in tomato and carrot, and whether this could be linked to structural changes. An in vitro approach was applied in order to screen a large number of processing parameters. The in vitro models mimicked different parts of the human gastrointestinal tract, and were used to assess the carotene release from the food matrix, micellar incorporation and cellular uptake. The predictive value of the in vitro models was evaluated by comparison with the in vivo bioavailability of β-carotene and lycopene from the same fruit and vegetable soups as measured in a human intervention study. The in vitro bioaccessibility of carotenes from carrot and tomato was generally improved by thermal and mechanical processing, and this could be linked to a reduction in cell wall integrity. High-pressure homogenisation (HPH) of carrot, causing extensive cell wall disintegration, and addition of 5% olive oil gave the highest in vitro bioaccessibility of α- and β-carotene. For these samples, the micellar incorporation of β-carotene was up to 69% of the total content. In addition, in vitro results for β-carotene were consistent with in vivo bioavailability. A combination of thermal and mechanical processing of tomato significantly increased the in vitro release of lycopene, but attempts to further increase the bioaccessibility by a second thermal treatment or by HPH were not successful. Consequently, the micellar incorporation remained below 22%, even with an addition of 5% olive oil. Furthermore, the in vitro models used to assess lycopene bioaccessibility could not predict in vivo measurements. In conclusion, processing conditions that reduced the cell wall integrity of tomato and carrot had a large positive effect on the in vitro bioaccessibility of carotenes and, with respect to β-carotene, also suggested an improved bioavailability as measured in humans.