Negative impact of soluble, gel-forming dietary fibres on the bioaccessibility of β-carotene, lutein, and lycopene

Carotenoids, including β-carotene, lutein and lycopene, the 3 main carotenoids present in our body, are lipophilic phytochemicals associated with several health benefits. Dietary fibre may influence the bioavailability of carotenoids by altering their release from the food matrix and their solubilisation into mixed micelles during digestion and thus their subsequent absorption by enterocytes. We examined the dose-dependent influence of major soluble (pectin, guar, alginate, fructooligosaccharides,) and insoluble dietary fibres (cellulose, type-2 resistant starch) at nutritional relevant doses (0, 30 and 90 mg per 26 ml) added for digestion, containing also pure β-carotene, lutein or lycopene (at 75 μg) solubilized in peanut oil. Following in vitro gastrointestinal digestions, carotenoid bioaccessibility, selected physico-chemical parameters (viscosity, surface tension, ζ-potential and micelle size) and free fatty acid release were evaluated. β-Carotene bioaccessibility was reduced by 90 mg of alginate and pectin, from 29.1% to 11.8% and 17.9%, respectively (p < 0.001), while other fibres had no overall significant impact. For lutein, only pectin decreased its bioaccessibility, from 58.3% to 26.0% (p < 0.001), while for lycopene, the reduction in bioaccessibility was from 7.2% (control) to 5.4% for pectin (p < 0.05), 4.1% for alginate (p = 0.001) and 4.8% for guar (p < 0.05) for 90 mg. This negative effect was associated with altered physico-chemical properties, with soluble, gel-forming fibres (vs. non-gel-forming fibres) in general increasing viscosity, reducing surface tension and absolute ζ-potential and in part micelle size, and hampering triglyceride digestion by up to 54.3% for guar (90 mg) vs. controls. Thus, soluble, gel-forming dietary fibres hampered carotenoid bioaccessibility, also depending on carotenoid type, while insoluble and non-gel-forming dietary fibres showed no negative effect on bioaccessibility.