ABSTRACT
Daidzein, an isoflavone found abundantly in legumes, may benefit from bypassing upper gut absorption to reach the colon where it can be metabolized into the potent estrogen equol by the gut microbiome. To achieve this, we developed mucin coated protein-tannin multilayer microcarriers. Highly porous functionalized calcium carbonate (FCC) microparticles efficiently absorbed daidzein from a dimethyl sulfoxide solution, with a loading capacity of 21.6 ± 1.8 wt% as measured by ultra-high pressure liquid chromatography - mass spectrometry (UPLC-MS). Daidzein-containing FCC microparticles were then coated with a bovine serum albumin (BSA)-tannin n-layer film terminated with mucin ((BSA-TA)n-mucin) by layer-by-layer deposition from corresponding aqueous solutions followed by FCC decomposition with HCl. Raman spectroscopy confirmed mucin-tannin complexation involving both hydrophobic interactions and hydrogen bonding. The resulting multilayer microcarriers contained 54 wt% of nanocrystalline daidzein as confirmed by X-ray diffraction and UPLC-MS. Preliminary screening of several types of mucin coatings using an in vitro INFOGEST digestion model demonstrated that mucin type III from porcine stomach provided the highest protection against upper intestinal digestion. (BSA-TA)8-mucin and (BSA-TA)4-mucin microcarriers retained 71 ± 16.4% and 68 ± 4.6% of daidzein, respectively, at the end of the small intestinal phase. Mucin-free (BSA-TA)8 retained a lower daidzein amount of 46%. Daidzein release and further conversion into equol were observed during in vitro colonic studies with fecal microbiota from a healthy non-equol-producing donor and Slackia equolifaciens. The developed approach has potential for encapsulating other hydrophobic nutraceuticals or therapeutics, enhancing their bioaccessibility in the colon.
