Phenolic Acids from Wheat Show Diﬀerent Absorption Proﬁles in Plasma: A Model Experiment with Catheterized Pigs Natalja P. Nørskov,* ,† Mette S. Hedemann, † Peter K. Theil, † Inge S. Fomsgaard, ‡ Bente B. Laursen, ‡ and Knud Erik Bach Knudsen † † Department of Animal Science, Faculty of Science and Technology, Aarhus University, Blichers Alle ́ 20, PO Box 50, DK-8830 Tjele, Denmark ‡ Department of Agroecology, Faculty of Science and Technology, Aarhus University, Forsøgsvej 1, DK-4200 Slagelse, Denmark ABSTRACT: The concentration and absorption of the nine phenolic acids of wheat were measured in a model experiment with catheterized pigs fed whole grain wheat and wheat aleurone diets. Six pigs in a repeated crossover design were ﬁtted with catheters in the portal vein and mesenteric artery to study the absorption of phenolic acids. The diﬀerence between the artery and the vein for all phenolic acids was small, indicating that the release of phenolic acids in the large intestine was not suﬃcient to create a porto-arterial concentration diﬀerence. Although, the porto-arterial diﬀerence was small, their concentrations in the plasma and the absorption proﬁles diﬀered between cinnamic and benzoic acid derivatives. Cinnamic acids derivatives such as ferulic acid and caﬀeic acid had maximum plasma concentration of 82 ± 20 and 200 ± 7 nM, respectively, and their absorption proﬁles diﬀered depending on the diet consumed. Benzoic acid derivatives showed low concentration in the plasma (<30 nM) and in the diets. The exception was p-hydroxybenzoic acid, with a plasma concentration (4 ± 0.4 μM), much higher than the other plant phenolic acids, likely because it is an intermediate in the phenolic acid metabolism. It was concluded that plant phenolic acids undergo extensive interconversion in the colon and that their absorption proﬁles reﬂected their low bioavailability in the plant matrix. KEYWORDS: phenolic acids, dietary ﬁber, plasma, pigs, wheat ■ INTRODUCTION Phenolic acids are considered ubiquitous among vascular plants, where they occur in most tissues. In cereals, phenolic acids are present in all cell tissues but with much higher concentrations in the aleurone and pericarp/testa layers compared to the endosperm. 1 Epidemiological studies have linked whole-grain cereal consumption with a reduced risk of developing colonic and breast cancer, arteriosclerosis, and type 2 diabetes. 1-3 The underlying physiological mechanism behind the protective eﬀects of whole-grain, however, are unclear but is most likely assigned to a concerted action of a wide variety of bioactive compounds, many of which are associated with the dietary ﬁber (DF) matrix. 1 Among the possible mechanisms, the antiox- idative capacity of phenolic acids most likely play a role even though the concentration level induced in vitro and ex vivo to obtain an eﬀect appears much higher than detected in vivo in both animals and humans. 4-7 Phenolic acids are hydroxylated derivatives of cinnamic and benzoic acids, Figure 1. Cinnamic acid derivatives found in wheat are ferulic acid, caﬀeic acid, p-coumaric acid, and sinapic acid, whereas protocatechuic acid, p-hydroxybenzoic acid, salicylic acid, vanillic acid, and syringic acid are derivatives of benzoic acid. Ferulic acid is the predominant phenolic acid in wheat, accounting for 70-90% of total phenolic acid content. 8 A small proportion of free phenolic acid is located in the outer layer of the pericarp. Free phenolic acids are absorbed in the small intestine and conjugated in the intestinal epithelium or in the liver. 9 Most phenolic acids in cereals, however, occur bound to plant cell walls, which consist of cellulose, arabinoxylan, and β-glucan. Ferulic acid, for instance, is linked to the O-5 position of the arabinofuranose substitutes in the arabinoxylan but may also be linked by ester and ether bonds to lignin. 10 In contrast to the free phenolic acids, bound phenolic acids have to be released from the plant matrix by intestinal esterases in the mucosa or, the main part, by bacterial esterases in the colon. 11 The bioavailability of phenolic acids depends largely on their bioaccessibily in the plant matrix. 8,12 In the process of microbial fermentation, however, plant phenolic acids are further metabolized to, i.e., derivatives of phenylpropionic, phenyl- acetic, hippuric, and benzoic acids with diﬀerent hydroxylation patterns. For instance, ferulic and caﬀeic acids can be de- esteriﬁed to 3-(3-hydroxyphenyl)-propionic acid and subse- quently β-oxidized to benzoic acid. The eﬃciency of release by intestinal and bacterial esterases and further metabolism of phenolic acids aﬀect their absorption pattern and their route of excretion, i.e., through feces or urine. 11,9 More knowledge concerning absorption and bioavailability of phenolic acids in plasma is therefore required to fully understand their physiological properties and potential health eﬀects in vivo. To our knowledge, previous studies on bioavailability and absorption of phenolic acids from wheat have primarily been performed with rats. 13,4 However, because the digestive physiology of pigs is more similar to humans than it is the case for rats, we used porto-arterial catheterized pigs to measure the net absorption of the nine phenolic acids present in wheat. Received: January 17, 2013 Revised: August 12, 2013 Accepted: August 24, 2013 Published: August 24, 2013 Article pubs.acs.org/JAFC © 2013 American Chemical Society 8842 dx.doi.org/10.1021/jf4002044 | J. Agric. Food Chem. 2013, 61, 8842-8850