Effects of selected extrusion parameters on physicochemical properties and in vitro starch digestibility and b-glucan extractability of whole grain oats Sandrayee Brahma a , Steven A. Weier b , Devin J. Rose a, * a Department of Food Science and Technology, University of Nebraska-Lincoln, Lincoln, NE, USA b The Food Processing Center, University of Nebraska-Lincoln, Lincoln, NE, USA article info Article history: Received 8 July 2015 Received in revised form 21 April 2016 Accepted 2 May 2016 Available online 3 May 2016 Keywords: Polysaccharides Expansion Processing Moisture abstract Whole grain oat flour was extruded under different moisture contents (15%, 18%, 21%), barrel tempera- tures (100  C, 130  C), and screw speeds (160 rpm, 300 rpm, 450 rpm), and selected physicochemical properties, in vitro starch digestibility, and b-glucan extractability of the extrudates were analyzed. An increase in screw speed resulted in an increase in radial expansion index, water absorption index, and water solubility index. Screw speed significantly affected slowly and rapidly digestible starch. Moderate screw speed (300 rpm) led to higher slowly digestible starch with an accompanying decrease in rapidly digestible starch. Low moisture conditions (15%) resulted in the highest resistant starch and water- extractable b-glucan. Under the conditions used in this study, extrusion did not result in changes in water-extractable b-glucan molecular weight. Thus, extrusion might be beneficial in improving func- tionality and consumer acceptability by affecting physicochemical properties, in vitro starch digestibility, and b-glucan extractability of oat extrudates. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Oats have been recognized for their nutritional properties. Oats, along with barley, are among the only grains that have received health claims in several countries for reduction in cholesterol (Tiwari and Cummins, 2009). The cholesterol-lowering ability of oats may be due to many components in the grain working syn- ergistically, but the b-glucan fraction seems to play a major role (Wolever et al., 2010). Oat b-glucan is a high molecular weight linear glucan consisting of (1 / 3) and (1 / 4) linkages. In the GI tract, b-glucan contributes viscosity, which slows the rate of cholesterol absorption and decreases enterohepatic recirculation of bile acids, thus reducing blood cholesterol (Queenan et al., 2007; Wolever et al., 2010). In addition to the cholesterol-lowering abil- ity of oats, the viscosity contributed by b-glucan may also contribute additional benefits such as reducing the rate of starch digestion and subsequent glycemic response (Brummer et al., 2012; Kim and White, 2013). A prevalent way of consuming oats is in the form of extruded ready-to-eat breakfast cereals. During extrusion, the grain is sub- jected to low moisture, high shear, and high temperature for a short time, after which the relief of pressure and reduction in tempera- ture causes moisture to flash off and produce an expanded product (Guy, 2001). Previous research has shown that extrusion can affect the solubility and molecular weight distribution of the poly- saccharides in grains. For instance, Zhang et al. (2011) extruded oat bran at 10e30% moisture using a twin screw extruder at 100e160  C and a screw speed of 150 rpm and found that extrusion increased the yield of soluble dietary fiber (principally b-glucan). In general, the yield of soluble dietary fiber increased as feed moisture decreased, while temperature had less of an influence on the sol- uble dietary fiber yield. The extracted soluble dietary fiber had a higher solubility and viscosity than that extracted from untreated oats. They suggest that the increase in yield could be due to more effective extraction of the higher-molecular weight b-glucan that was unextractable prior to extrusion (Zhang et al., 2009). In contrast to Zhanget al. (2011), Tosh et al. (2010) showed dramatic Abbreviations: REI, radial expansion index; WAI, water absorption index; WSI, water solubility index; RDS, rapidly digestible starch; SDS, slowly digestible starch; RS, resistant starch. * Corresponding author. 268 Food Innovation Center, 1901 North 21st Street, P.O. Box 886205, Lincoln, NE 68588-6205, USA. E-mail address: drose3@unl.edu (D.J. Rose). Contents lists available at ScienceDirect Journal of Cereal Science journal homepage: www.elsevier.com/locate/jcs http://dx.doi.org/10.1016/j.jcs.2016.05.001 0733-5210/© 2016 Elsevier Ltd. All rights reserved. Journal of Cereal Science 70 (2016) 85e90