Article pubs.acs.org/JAFC
Production and in Vitro Fermentation of Soluble, Non-digestible, Feruloylated Oligo- and Polysaccharides from Maize and Wheat Brans Junyi Yang, María X. Maldonado-Gómez, Robert W. Hutkins, and Devin J. Rose* Department of Food Science and Technology, University of NebraskaLincoln, Lincoln, Nebraska 68583-0919, United States S Supporting Information *
ABSTRACT: High-pressure hydrothermal treatment of cereal bran results in fragmentation of the cell wall, releasing soluble, non-digestible, feruloylated oligo- and polysaccharides (FOPS), which may be beneficial to gut health. The objectives of this study were to (1) determine treatment temperatures for production of FOPS from maize bran and wheat bran and (2) determine the fermentation properties of partially purified FOPS from maize bran and wheat bran. FOPS were produced by heating bran and water (10%, w/v) in a high-pressure stirred reactor until the slurry reached 160−200 °C (in 10 °C increments). Final temperatures of 190 °C for maize bran and 200 °C for wheat bran resulted in the highest release of FOPS (49 and 50% of starting non-starch polysaccharide, respectively). Partial purification with ion exchange and dialysis resulted in a final product containing 63 and 57% total carbohydrate and 49 and 30% FOPS, respectively (other carbohydrate was starch). Following in vitro digestion (to remove starch), in vitro fermentation revealed that wheat FOPS were more bifidogenic than maize FOPS. However, maize FOPS led to continual production of short-chain fatty acid (SCFA), resulting in the highest SCFA and butyrate production at the end of the fermentation. In addition, maize FOPS showed significantly higher antioxidant activity than wheat FOPS. This study identified a process to produce FOPS from maize bran and wheat bran and showed that, considering the overall beneficial effects, FOPS from maize bran may exhibit enhanced benefits on gut health compared to those of wheat bran. KEYWORDS: maize, short-chain fatty acids, butyrate, prebiotic, Bif idobacterium
■
INTRODUCTION The basic structure of arabinoxylan, the predominant nonstarch polysaccharide in grains, is a (1,4)-linked β-Dxylopyranosyl backbone substituted at C(O)-2 and/or C(O)3 with α-L-arabinofuranosyl moieties, some of which are themselves substituted with ferulic acid that can be involved in oxidative cross-linkages with other arabinoxylan chains and other cell-wall components.1 Beyond these basic structures, arabinoxylan can also contain oligosaccharide side chains comprised of pentose or hexose sugars or uronic acids. Dependent upon botanical source and location within the kernel, arabinoxylan can differ in distributions and types of side chains, molecular weight, ferulate content, and degree of crosslinking.1,2 Because of its complex nature, arabinoxylan is sometimes referred to as glucuronoarabinoxylan or heteroxylan.3−5 For simplicity, arabinoxylan will be used in this paper to refer to this complex class of polysaccharides. Two sources of divergent arabinoxylan structures are those from maize and wheat. Enzymatic or dilute acid degradation accompanied by partial methylation analysis of alkali-solubilized arabinoxylan from maize bran and wheat bran has revealed greater branch density and complexity in maize arabinoxylan compared to that of wheat.4,6,7 In its native form, arabinoxylan is mostly insoluble and crosslinked, making it a poorly fermentable substrate for gut bacteria.8−10 However, partial hydrolysis of arabinoxylan from wheat bran with xylanase releases arabinoxylan oligosaccharides (AXOS), which are highly fermentable in the gut and stimulate the growth of bifidobacteria and other beneficial bacteria.11 © 2013 American Chemical Society
AXOS have also been shown to reduce blood serum triglyceride and cholesterol levels, facilitate diabetic weight loss, and enhance antioxidant capacity in liver.11 Arabinoxylan may also be released from its insoluble matrix by autohydrolysis,12,13 but the structure of the carbohydrates released are different from those released by enzyme. For instance, autohydrolysis breaks down the arabinoxylan into many size pieces ranging from monosaccharides on up to polysaccharides with a degree of polymerization (DP) of 750 or more,12,13 while enzymatic treatment releases mostly shorter chain oligosaccharides.14 Additionally, autohydrolysis can release arabinoxylan structures that are resistant to enzymatic hydrolysis, as evidenced by increased yields with autohydrolysis (ca. 50% from maize bran and wheat bran)12,13 compared to enzymatic release (ca. 30% in wheat bran10,14 and
