The objective of this study was to examine the impact of flow conditions during the stomach phase of a simple in vitro digestion procedure on the microstructural properties and the β-carotene bioaccessibility of carrot-based model food systems containing oil and different barriers for βcarotene bioaccessibility. A 'periodic forces' stomach model, in which the flow characteristics (measured by Particle Image Velocimetry) corresponded well with experimental in vivo and in silico literature data, was successfully developed and implemented and used in a two-step static in vitro digestion procedure. This stomach model was compared with a conventional end-over-end rotation stomach model in which flow conditions were uncontrolled. Both models in combination with an end-over-end intestinal phase revealed differences in β-carotene bioaccessibility of carrot-based fractions due to the presence of different barriers (the plant chromoplast structure and/or the cell wall). Absolute β-carotene bioaccessibility values however differed between the models. The periodic forces stomach flow behavior lowered the β-carotene bioaccessibility in the β-carotene-enriched emulsion (72% versus 45%), the chromoplast fraction (66% versus 36%) and the large cell cluster fraction (22% versus 13%). The model also resulted in the presence of clusters of small oil droplets interspersed by surface-active compounds while large, coalesced oil droplets (D(v;0.9) of 189 µm) were observed after digestion in the end-over-end stomach model. As a consequence of the periodic forces stomach flow behavior also a slightly higher disintegration of carrot particles (to a D(v;0.9) of 450 µm instead of 492 µm) was observed which was however not linked to a higher β-carotene bioaccessibility in carrot cell clusters.Food industry has great interest in carotenoids because this group of fat-soluble bioactive compounds seems to have a positive impact on human health, including antioxidant capacity, provitamin A activity and immune system enhancing properties (Dutta et al., 2005;Fernandez-Garcia et al., 2012). Since mammals need to obtain carotenoids from their diet, maximal absorption, or bioavailability of carotenoids from the food is desirable. Bioavailability is the fraction of the ingested carotenoids that is available for utilization in physiological functions and for storage in the body. It is partially determined by bioaccessibility, which is the fraction of the ingested carotenoids that is incorporated into micelles and thus becomes available for absorption in the body (Hedrén et al., 2002;Palafox-Carlos et al., 2011). Carotenoid bioaccessibility depends on several factors, such as the presence of oil and the matrix in which the carotenoids are embedded (Castenmiller & West, 1998;Hedrén et al., 2002). This is because on the one hand carotenoids are lipophilic molecules, and thus need to be incorporated in micelles before they can be absorbed and on the other hand because the localization of carotenoids within the plant structure is important. Carotenoids are l...