CEREAL CHEMISTRY 294 Synergistic and Additive Effects of Three High Molecular Weight Glutenin Subunit Loci. I. Effects on Wheat Dough Rheology S. Uthayakumaran, 1,2 H. L. Beasley, 3 F. L. Stoddard, 4 M. Keentok, 1,2 N. Phan-Thien, 1,2 R. I. Tanner, 1,2 and F. Békés 1,3,5 ABSTRACT Cereal Chem. 79(2):294–300 The high molecular weight glutenin subunits (HMW-GS) play an important role in governing the functional properties of wheat dough. To understand the role of HMW-GS in defining the basic and applied rheo- logical parameters and end-use quality of wheat dough, it is essential to conduct a systematic study where the effect of different HMW-GS are determined. This study focuses on the effect of HMW-GS on basic rheological properties. Eight wheat lines derived from cvs. Olympic and Gabo were used in this study. One line contained HMW-GS coded by all three loci, three lines were each null at one of the loci, three lines were null at two of the loci and one line null at all three loci. The flour protein level of all samples was adjusted to a constant 9% by adding starch. In another set of experiments, in addition to the flour protein content being held at 9%, the glutenin-to-gliadin ratio was maintained at 0.62 by adding gliadin. Rheological properties such as elongational, dynamic, and shear viscometric properties were determined. The presence of Glu-D1 subunits (5+10) made a significantly larger contribution to dough prop- erties than those encoded by Glu-B1 (17+18), while subunit 1, encoded by Glu-A1, made the least contribution to functionality. Results also confirmed that HMW-GS contributed to strength and stability of dough. Understanding the role of the various constituents of wheat flour in determining the functional properties of dough has been a major endeavor throughout the 20th century. With this knowledge, better wheat cultivars can be bred and more economical manufac- turing technologies can be developed. The protein in wheat is mainly responsible for inherent differences in baking quality (Finney 1943), with both quantity and quality of the protein being important (Finney and Barmore 1948). It has been well established that two classes of proteins, glutenins and gliadins, are the key components in deter- mining the rheological properties of dough as they interact to form the gluten matrix during dough mixing. Glutenins are polymers of high molecular weight glutenin subunits (HMW-GS) and low molecular weight glutenin subunits (LMW-GS), which differ in their mobility during SDS-PAGE. The HMW-GS have the largest role in defining dough strength (MacRitchie 1992) and possibly stability (Payne 1987). Bread wheat (Triticum aestivum L. emend Thell.) is a hexaploid species with three genomes designated A, B, and D. The Glu-1 loci on the long arms of the homoeologous Group 1 chromosomes code for the HMW-GS, and are designated Glu-A1, Glu-B1 and Glu-D1, respectively. Each locus generally codes for two subunits, “x” and “y”, although the Glu-A1 y-type gene is usually not expressed. Each locus also has several alleles, differences between which account for a considerable proportion of the variation in dough strength (Payne et al 1987). Null alleles, where no subunits are produced at all, have been developed at each of the three Glu-1 loci (Lawrence et al 1988). This set of lines provides a valuable resource for identifying the effect of each Glu-1 locus on overall rheology and end-product quality. The set has already been used for studies on polymeric protein formation (Gao and Bushuk 1993; Gupta et al 1995), but without correction to a constant protein content. For these reasons, basic rheological tests (elongational, shear viscometry, and dynamic oscillatory tests) and end-use quality tests (breadmaking) were conducted. Fundamental or basic rheological tests are considered to be valuable tools in determining dough functionality and unlike the empirical dough measurement tests (mixograph, farinograph, extensigraph, and alveograph), are founded on parameters of basic physics (Levine 1987). The rheological prop- erties of dough change considerably during every baking phase and the viscoelastic properties of dough have a profound effect on the finished product (Walker and Hazelton 1996). The basic rheo- logical measurements can be used for constitutive modeling of bread dough and this may lead to predictions of dough processing behavior. MATERIALS AND METHODS The eight flour samples differed by the activity (designated +) or inactivity (designated – or null) of each of the three glutenin loci (Table I). The ash content was determined using Approved Method 08-01 (AACC 2000). The nitrogen content of the flours was deter- mined by the Dumas total combustion method using an elemental analyzer (CHN–1000, Leco Inc., St Joseph, MI). The protein content (%) was determined as N × 5.7. The moisture content of the flours was determined by a near infrared spectrometer with sample transport (Foss NIRSystems 6500, Silver Spring, MD). Flour protein level of all samples was adjusted to a constant 9% by adding commercial wheat starch (1.6% protein). The ratio of glutenin to gliadin, ratio of high molecular weight glutenin subunits to low molecular weight glutenin subunits (HMW-GS/LMW-GS ratio) and the unextractable polymeric protein percentage (% UPP) (Table I) of the samples were determined using reversed-phase HPLC (Marchylo et al 1989) and size-exclusion HPLC (Singh et al 1990; Batey et al 1991; Gupta et al 1993), respectively. The effect of maintaining the glutenin-to-gliadin ratio constant was investigated in a subset of the flours. The choice of materials was limited to four by the quantity of flour available. Gliadin (85% protein) was extracted from flour of the line null for all three HMW- GS loci using the mild pH extraction method of MacRitchie (1985). Lyophilized gliadin was added to + + +, + – + and – – + flours to achieve a uniform glutenin-to-gliadin ratio of 0.62, as found in the – – – sample. Commercial starch was also added to maintain the constant protein content of 9%. Mixing was conducted at a water absorption of 57%. Blended flour and water were mixed in a 10-g mixograph to peak dough development and rheological measurements were then made. Mixing was done in triplicate for each sample and the mean peak dough development time was calculated from the mixing curve (Gras et al 1990). 1 Quality Wheat Cooperative Research Centre Ltd., Locked Bag 1345, North Ryde, NSW 1670, Australia. 2 Department of Mechanical and Mechatronic Engineering, University of Sydney, NSW 2006, Australia. 3 CSIRO Plant Industry, Grain Quality Research Laboratory, PO Box 7 North Ryde, NSW 1670, Australia. 4 School of Applied Sciences, University of Wolverhampton, Wulfruna St., Wolverhampton WV1 1SB, UK. 5 CSIRO Plant Industry, GPO Box 1600 Canberra, ACT 2601, Australia. Corres- ponding author: Phone (Sydney Office): +61 2 9490 8437. Fax: +61 2 9490 8419. E-mail: F.Bekes@pi.csiro.au Publication no. C-2002-0211-02R. © 2002 American Association of Cereal Chemists, Inc.