Adaption of an in vitro digestion method to screen carotenoid liberation and in vitro accessibility from differently processed spinach preparations.

Dark green leafy vegetables are primary food sources for lutein and ß-carotene, however these bioactives have low bioavailability. The effects of mechanical and thermal processing as well as fat addition and fat type on lutein and ß-carotene liberation and in vitro accessibility from spinach were investigated. Lutein liberation and in vitro accessibility were three-fold higher from spinach puree compared to whole leaves. Results for ß-carotene liberation were similar, whereas that of ß-carotene accessibility was only about two-fold. Steaming had no or a negative effect on carotenoid liberation. Fat addition increased ß-carotene liberation from raw and steamed puree, but reduced lutein liberation from steamed leaves and raw puree. Fat types affected ß-carotene differently. Butter addition led to a 2.5 fold increased liberation from raw spinach puree, while the effect of olive and peanut oil was significantly lower, but only minor effects were observed for lutein.

In vitro liberation of carotenoids from spinach and Asia salads after different domestic kitchen procedures.

Green-leafy vegetables are rich in nutritionally important constituents including carotenoids. Their potential health benefits depend among others on their liberation from the plant matrix. The aim of the present study was to evaluate the effect of particle size and heat treatments on lutein and ß-carotene liberation from spinach and Asia salads by applying an in vitro digestion protocol and UHPLC analysis. Reduction of particle size resulted in a three- to fourfold increase in liberation of lutein and ß-carotene when comparing whole leaf and puree preparations of spinach. However, this positive effect was shown to be nullified by the severe heat impact during stir-frying of minced spinach, showing that domestic treatments need to be chosen carefully to maximise carotenoid liberation. Steaming significantly improved lutein liberation from Asia salads, but had no or a negative effect in spinach samples, possibly due to differences in liberation or degradation between the two plant matrices.