Distribution and characterisation of fructan in wheat milling fractions L. Haskå a, * , M. Nyman a , R. Andersson b a Applied Nutrition and Food Chemistry, Department of Food Technology, Engineering and Nutrition, Chemical Center, Lund University, P.O. Box 124, SE-22100 Lund, Sweden b Department of Food Science, Swedish University of Agricultural Sciences, Uppsala, Sweden article info Article history: Received 16 January 2008 Received in revised form 30 April 2008 Accepted 9 May 2008 Keywords: Fructan Arabinoxylan Wheat Molecular weight abstract Structure and health effects of inulin-type fructans have been extensively studied, while less is known about the properties of the graminan-type fructans in wheat. Arabinoxylan (AX) is another important indigestible component in cereal grains, which may have beneficial health effects. In this study, the fructan content in milling fractions of two wheat cultivars was determined and related to ash, dietary fibre and AX contents. The molecular weight distribution of the fructans was analysed with HPAEC-PAD and MALDI-TOF MS using 1 H NMR and enzymatic hydrolysis for identification of fructans. The fructan content (g/100 g) ranged from 1.5  0.2 in flour to 3.6  0.5 in shorts and 3.7  0.3 in bran. A correlation was found between fructan content and dietary fibre content (r ¼ 0.93, P < 0.001), but with a smaller variation in fructan content between inner and outer parts of the grain. About 50% of the dietary fibre consisted of AX in all fractions. The fructans were found to have a DP of up to 19 with a similar molecular weight distribution in the different fractions. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Fructans are carbohydrates consisting of fructosyl units with or without one glucosyl unit. The different types of fructans found in nature may be classified according to linkage and origin as sug- gested by Roberfroid (2005). Linear-type fructans contain pre- dominantly one type of fructosyl-fructose linkage; b-(1 / 2) in inulin and b-(6 / 2) in levan (mostly from bacteria) and phlein (from plants). Graminan-type fructans contain both b-(1 / 2) and b-(6 / 2) linkages. Inulin from chicory root has been extensively studied regarding structure (De Leenheer and Hoebregs, 1994; Timmermans et al., 2001; van Loo et al., 1995) and health effects and has been found to increase mineral absorption, reduce cho- lesterol levels and have bifidogenic effects (Roberfroid, 2005). In- terestingly, different molecular weights of inulin have been shown to affect the formation of colonic short-chain fatty acids (SCFAs) differently, i.e. the main end products of colonic fermentation, where some may have health-promoting effects (Nilsson and Nyman, 2005). Considerably less is known about the properties of other types of fructans, such as the graminan-type fructans found in wheat. The fructan content in wheat grains has been determined to be 0.9–1.8 g/100 g in five cultivars from five growth places (Fretzdorff and Welge, 2003). The content has been found to be higher in bran (2.0 g/100 g) and middlings (2.3 g/100 g) than in flour (1.6 g/100 g) and grain (1.5 g/100 g) (Knudsen, 1997). In the study of Fretzdorff and Welge (2003), fructans were estimated to have an average DP of 5–7 in most whole grain samples. Other studies have shown that 40–50% of fructans from wheat flour (Nilsson et al., 1986) and 60% from whole grains (Henry and Saini, 1989) have a DP of less than 6. Further, fructans in wheat flour have been reported to have a highest DP of 7–8 (van Loo et al., 1995) and 16 (Nilsson et al., 1986). The inconsistent results regarding DP in different studies may be caused not only by different samples but also by the use of different analytical methods. Today, more advanced and accurate methodologies are available. High-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC- PAD) is a useful technique for separating fructans (Cataldi et al., 2000; Corradini et al., 2004). However, it is difficult to determine the DP of a non-linear series without available standards as several peaks may correspond to the same DP. These analyses can be complemented with matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOF MS), which measures the molec- ular weight regardless of branching structure (Lopez et al., 2003; Losso and Nakai, 1997). Fructan is an indigestible carbohydrate entering the colon, and therefore acts as a dietary fibre component, i.e. indigestible poly- saccharides and lignin as defined by Trowell (1976). However, Abbreviations: Ara, arabinose; Ara/Xyl, arabinose to xylose ratio; AX, arabinox- ylan; DP, degree of polymerisation; Fru, fructose; Gal, galactose; Glc, glucose; HPAEC-PAD, high performance anion-exchange chromatography with pulsed amperometric detection; MALDI-TOF MS, matrix-assisted laser desorption time-of- flight mass spectrometry; NMR, nuclear magnetic resonance; SCFA, short-chain fatty acid; Xyl, xylose. * Corresponding author. Tel.: þ46 46 2224727; fax: þ46 46 2224532. E-mail address: lina.haska@appliednutrition.lth.se (L. Haskå). Contents lists available at ScienceDirect Journal of Cereal Science journal homepage: www.elsevier.com/locate/jcs 0733-5210/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jcs.2008.05.002 Journal of Cereal Science 48 (2008) 768–774