Structural features of cereal bran arabinoxylans related to colon fermentation rate

Pinthip Rumpagaporn, Purdue University

Abstract

Soluble and fermentable fibers provide numerous benefits to host health due to the production of short chain fatty acids. Gas produced during fermentation is a concern of fermentable fiber intake, causing bloating and flatulence in commercial prebiotics such as fructooligosaccharides. Alkali-extractable arabinoxylans from various cereal brans have shown different fermentation patterns. Fiber with initial slow and complete fermentation is desirable both to overcome the problem of gas production and to provide fermentable substrate to the mid and distal colon. In this study, three different types of modifications have been conducted to investigate the factors that slow initial rate of fermentation, as well as provide some extent of extended fermentation. First, enzymatic modification with endoxylanase and graded ethanol precipitation were used to obtain alkali-extractable arabinoxylans in varying molecular size, degree of substitution, and degree of branching indicated by the arabinose:xylose ratio. Molecular size, degree of substitution, and arabinose:xylose ratio of highly branched arabinoxylans showed no relationship to fermentation patterns. The linkage-type of the branches was the major structural feature of highly branched arabinoxylans that promoted slow fermentation. Branches containing single xylose units were the most significant in this regard, followed by oligosaccharide side chains with two second level sugars linked at O-2,3 of the arabinose residues. Oligosaccharide side chains with the second sugar (xylose, arabinose, or galactose) linked at O-2, O-3, and O-5 of the arabinose residues were the least important with respect to slow fermentation. Second, chemical modification by acid and graded ethanol precipitation was performed to produce arabinoxylooligosaccharides hypothesized to have slow fermenting linkages identified above. However, all acid-hydrolyzate fractions were fermented rapidly, caused by the loss of all single arabinose unit side chains and some di/trisaccharides side chains. In this case, the degree of substitution and type of linkage of the branched constituents affected the rate of fermentation more than the degree of polymerization. Third, mechanical modification (ball milling) was applied to obtain smaller arabinoxylan structures, and confirmed that fermentation rate is influenced by the quantity and type of linkage of the branched constituents rather than molecular size and showed that smaller arabinoxylan polymers retained both branch linkages and the slow fermentation property. The application of alkali-extractable corn arabinoxylan and its hydrolyzate in foods was also tested. Only corn xylanase-treated hydrolyzate had both a high pH and heat stability, low shear thinning viscosity and only slightly discolored solutions, giving it the potential to be used in high fiber drinks while retaining beneficial initial low gas production and extended fermentation.

Degree

Ph.D.

Advisors

Hamaker, Purdue University.

Subject Area

Food Science|Nutrition

COinS