Schematic presentation on the effect of aleurone structure on ferulic acid absorption from the different diets. 1. Free FA (a) is readily absorbed to the portal vein from the stomach and upper parts of the intestine. In the diet A4 majority of FA is in free form due to xylanase and feruloylesterase pretreatments. 2. The diet A3 contains xylanase treated aleurone and has a mixture of both free and bound FA and is therefore in brackets. Whereas, in the diets containing intact (A1) or cryo-ground aleurone (A2) majority of FA is tightly bound to the arabinoxylan fibre matrix, and bioavailability of FA is thus dependent on its release by the microbial enzymes within the caecum (mice) and colon. 3. Most of the microbially released FA is further metabolized by the microbial enzymes. The modifications include reduction of FA into dihydroferulic acid (b), further demethylation to form dihydroxyphenylpropionic acid (DHPPA) (c), dehydroxylation into hydroxyphenylpropionic acid (HPPA) (d), and finally after another dehydroxylation step and beta-oxidation to benzoic acid (e). All of these intermediate metabolites can be absorbed to circulation, however, part of them are excreted in faeces. 4. All the absorbed compounds can be further metabolized in liver via phase I xenobiotic metabolism or directly conjugated either with sulfate, glucuronide, or amino acids such as glycine and excreted in urine (phase II). When FA is absorbed from the upper parts of the intestine the main metabolites found in urine are ferulic acid sulfate (f), and feruloylglycine (g). When dietary FA is mainly bound to AX-fibre matrix the main urine metabolites are hippuric acid (h), DHPPA sulfate (i), and HPPA sulfate (j).