Abstract
BackgroundPhenolic acids are covalently bound to the arabinoxylan fibre matrix of wheat aleurone layer. In order to be bioavailable they need to be released by endogenous or bacterial enzymes and absorbed within the intestinal lumen. The intestinal microbiota can metabolize phenolic acids and other food-born phytochemicals. However, the effect of structure of the cereal bran or aleurone layer on these processes is not comprehensively studied.MethodsThe structure of aleurone layer was modified either by dry-grinding or by enzymatic treatments with xylanase alone or in combination with feruloyl esterase. Diet induced obese C57BL6/J mice were fed with high-fat diets containing either pure ferulic acid, or one of the four differentially treated aleurone preparations for 8 weeks. The diets were designed to be isocaloric and to have similar macronutrient composition. The urinary metabolite profiles were investigated using non-targeted LC-qTOF-MS-metabolomics approach.ResultsThe different dietary groups were clearly separated in the principal component analysis. Enzymatic processing of aleurone caused increased excretion of ferulic acid sulfate and glycine conjugates reflecting the increase in unbound form of readily soluble ferulic acid in the diet. The urinary metabolite profile of the diet groups containing native and cryo-ground aleurone was more intense with metabolites derived from microbial processing including hippuric acid, hydroxyl- and dihydroxyphenylpropionic acids. Furthermore, aleurone induced specific fingerprint on the urinary metabolite profile seen as excretion of benzoxazinoid metabolites, several small dicarboyxlic acids, and various small nitrogen containing compounds.ConclusionsThe structural modifications on wheat aleurone fraction resulted in altered metabolism of aleurone derived phenolic acids and other phytochemicals excreted in urine of diet-induced obese mice.
Highlights
Phenolic acids are covalently bound to the arabinoxylan fibre matrix of wheat aleurone layer
AX makes the aleurone rich in dietary fibre (DF), and rich in bioactive phenolic compounds as the arabinose residues of AX are generally highly substituted with phenolic acid residues such as ferulic acid (FA), which is the major phenolic acid present in the aleurone layer
Following treatments were applied on the native aleurone (A1) to obtain three modified aleurone preparations: ultra-fine grinding with an impact mill in cryogenic conditions (A2), which produced an aleurone fraction with smaller particle size (1/3 of the native one); xylanase treatment (A3), which solubilized 43% of AX and released 17% of FA in a bioavailable form; successive xylanase and A-type feruloyl esterase (FAE) treatments (A4) which solubilized 82% of AX and released 87% of FA in bioavailable forms [14]
Summary
Wheat aleurone preparations and composition of diets The wheat aleurone-rich fraction (A1) was provided by Bühler AG (Uzwil, Switzerland). Animals and study design The details of the study design and animal trial are described by Rosa et al This resulted in 106 entities that were further reduced to 50 metabolites after cleaning the data from fragments and dimers of the molecular ions, from entities having high (>20%) RSD values in more than 3 out of 6 conditions, peaks with bad quality, or entities with clearly integration mistakes. The normalized data were clustered into three K-means clusters according to metabolites using a Pearson correlation as a distance metric method with maximum of 50 iterations
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