Partial disintegration of vegetable cell wall during cooking improves vitamin K1 (phylloquinone) bioaccessibility in in vitro digestion
Résumé
Vegetables rich in vitamin K consumption could prevent bleeding and maintain bone status. The aims of the present work were to investigate i) the effect of household cooking (i.e., boiling for 5 min at 100 °C in distilled water and stir-frying for 3 min at 180 °C in hot canola oil) on phylloquinone bioaccessibility of five rich phylloquinone leafy vegetables, namely Water spinach (Ipomoea aquatic Forssk), Amaranth (Amaranthus blitum subsp. oleraceus L.), Chinese broccoli (Brassica alboglabra), Pak choi (Brassica rapa L.) and Drumstick (Moringa oleifera Lam.), and ii) the structural changes of these leaves before and after in vitro gastro-intestinal digestion. All the experiments were realized in triplicate for each vegetable. The amounts of phylloquinone in leafy vegetables were noticeable in almost all species and ranged from 94 to 182 μg/100 g DM. Their cell wall polysaccharide contents greatly varied from 4.3 to 8.4 g for 100 g. The content in bioaccessible phylloquinone was low in raw leaves (<25 μg/100 g DM) as well as its bioaccessibility (<15%). Leaf pectin content impaired phylloquinone bioaccessibility using principal component analysis. Boiling and stir-frying significantly improved the bioaccessibility of phylloquinone in leaves by a factor of three to twelve and two to seven respectively (p<0.05). These variations were associated with changes in leaf structure. Palisade and spongy cells appeared ruptured and disorganized after stir-frying. Given the estimated bioaccessibility of phylloquinones, the consumption of 500 g of cooked wet leaves per day would cover phylloquinone needs of an individual adult average body weight.