Carbohydrate Polymers 82 (2010) 46–53 Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol Diffusion and viscosity in arabinoxylan solutions: Implications for nutrition Kinnari J. Shelat a , Francisco Vilaplana a , Timothy M. Nicholson b , Kok Hou Wong a , Michael J. Gidley a , Robert G. Gilbert a,∗ a The University of Queensland, Centre for Nutrition & Food Sciences, School of Land Crop & Food Sciences, Brisbane, Qld 4072, Australia b The University of Queensland, Centre for High Performance Polymers, School of Chemical Engineering, Brisbane, Qld 4072, Australia article info Article history: Received 15 February 2010 Accepted 12 April 2010 Available online 18 April 2010 Keywords: Arabinoxylan Non-starch polysaccharide Viscosity Diffusion Digestion Size-exclusion chromatography abstract Non-starch polysaccharides such as arabinoxylans have important roles in the human diet, resulting in potential benefits such as increased microbial fermentation, promotion of beneficial microflora, preven- tion of re-absorption of bile acids leading to lower plasma cholesterol, and retardation of starch digestion. The latter two beneficial effects may arise from viscosity and/or diffusion phenomena in the gastroin- testinal tract. To study this, measurements of the viscosity and diffusion coefficients of a polymer probe similar in size to both bile salt micelles and alpha-amylase were carried out for water solutions of three arabinoxylans with differing viscosities. Diffusion coefficients were obtained using fluorescence recovery after photobleaching (FRAP). The concentration dependence of both viscosity and diffusion coefficients followed the usual behaviour of polymers for each of three arabinoxylan samples. However, at a given concentration, the sample with the highest viscosity also had the highest probe diffusion coefficient: the reverse of what would be expected for homogeneous solutions. This apparent anomaly is ascribed to differences in polymer structure between the three samples giving rise to varying levels of local poly- mer aggregation and consequent microvoids. These differences are verified using characterisation with multiple-detection size-exclusion chromatography. Deviations from simple Stokes–Einstein behaviour are ascribed to the existence of aggregates in solution. The results show that studies of the role of ara- binoxylans in human nutrition cannot assume that the diffusion coefficients of species with sizes in the range important for digestive processes in a series of samples will increase with decreasing viscosity at a given concentration: diffusion coefficient and viscosity must be measured independently. © 2010 Elsevier Ltd. All rights reserved. 1. Introduction Cereal grains, important for human nutrition, mainly consist of starch and protein together with non-starch polysaccharides (NSPs). These NSPs are major component of cell walls, particularly in the starchy endosperm (Saulnier, Guillon, Sado, & Rouau, 2007, Saulnier, Sado, Branlard, Charmet, & Guillon, 2007). Although NSPs typically represent only about 3–8% of the total of the grain, they have major effects on the technological use and nutritional value of cereal grains due to their hydration properties, viscosity in aqueous solution, and consequent role as dietary fibre. Arabinoxylan (AX) is the major NSP of wheat endosperm cell walls and shows quantita- tive differences in structural features depending on tissue location as well as grain species (Saulnier, Guillon, et al., 2007; Saulnier, Sado, et al., 2007). AX is a copolymer with a linear backbone of (1–4)-linked -d-xylopyranosyl units; these -d-xylopyranosyl units are substituted at some O 2 and/or O 3 positions with -l- ∗ Corresponding author. Tel.: +61 7 3365 4809; fax: +61 7 3365 1188. E-mail address: b.gilbert@uq.edu.au (R.G. Gilbert). arabinofuranose. Some of these arabinofuranose units are esterified with ferulic acid, with the consequent potential for oxidative cross- linking. Diverse physicochemical properties, particularly solubility and network formation, can result from variation in the level and pattern of arabinose substitution and the extent of cross-linking via ferulic acid substituents (Saulnier, Guillon, et al., 2007; Saulnier, Sado, et al., 2007). The structure of AX, its physicochemical properties, and its role in food quality and beneficial health effects, have received some attention in the literature (Hoffmann, Kamerling, & Vliegenthart, 1992; Izydorczyk & Biliaderis, 1992, 1995; Knudsen & Jorgensen, 2007; Pitkanen, Virkki, Tenkanen, & Tuomainen, 2009; Saulnier, Guillon, et al., 2007; Saulnier, Sado, et al., 2007; Warrand et al., 2005). AX is a recognised dietary fibre, and has been reported to lower cholesterol absorption, to improve metabolic control in type 2 diabetes subjects, and to increase microbial fermentation and pro- mote microbial flora in the large intestine (Hanai et al., 1997; Lopez et al., 1999; Lu, Walker, Muir, & Dea, 2004). Despite this importance, AXs are considerably less studied than other NSPs such as (1,3;1,4)- -d-glucan (‘-glucan’) and guar galactomannan. Blackburn and Johnson (1981) and Jenkins et al. (1978) measured changes in the 0144-8617/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbpol.2010.04.019