Relationships of Quality Characteristics with Size-Exclusion HPLC Chromatogram of Protein Extract in Soft White Winter Wheats

Cereal Chem. 86(2):197–203 This study investigated relationships between molecular weight distributions of unreduced grain proteins and grain, flour, and end-use quality characteristics of soft white winter wheats grown in Oregon. Absorbance area and area percentage values of protein fractions separated by sizeexclusion HPLC (SE-HPLC) showed significant correlations with quality characteristics, indicating associations of molecular weight distributions of proteins with quality characteristics. Specifically, high molecular weight polymeric protein fractions appeared to have a detrimental effect on soft wheat quality. This was shown by significant positive correlations with single kernel hardness index, and mixograph water absorption and tolerance, and negative correlations with break flour yield, cookie diameter, and cake volume. Higher proportions of soluble monomeric protein fraction eluted after the main gliadin peak, were associated with soft wheat quality due to negative associations with single kernel hardness index and mixograph water absorption and tolerance, and positive associations with break flour yield, cookie diameter, and cake volume. Calibration models were developed by the application of multivariate analyses to the SE-HPLC data. These models explained >90% of the variation in mixograph water absorption and cookie diameter and thickness. Baking quality of soft wheat is generally evaluated by experimental sugar-snap cookie making. It is commonly assumed that flour that produces sugar-snap cookies with larger diameters and with a more obvious and uniform cracking pattern on the top surface is associated with increased tenderness and better quality in most soft wheat products, except for crackers (Wade 1988; Miller and Hoseney 1997). One of the most important quality factors used to select wheat for cookie making is kernel hardness. Wheat kernel hardness affects break flour yield, flour particle size distribution, and damaged starch content of flour (Wade 1988). When compared with hard wheat, soft wheat cultivars, in general, produce a higher yield of break flour with a smaller particle size distribution, and lower protein and starch damage, all of which are usually desirable for cookie and cake baking (Rogers et al 1993; Labuschagne et al 1997; Faridi et al 2000). Wheat hardness is affected by variations in puroindolines and lipids associated with starch granule surfaces (Greenblatt et al 1995; Giroux and Morris 1997). However, puroindolines are not fully responsible for variation of kernel texture when the tested wheat cultivars are limited within a class (Campbell et al 1999; Giroux et al 2000; Morris et al 2004, 2005). Significant genetic variation in hardness has been attributed to factors other than puroindolines such as water solubles, lipids, and pentosans (Bettge and Morris 2000; Giroux et al 2000; Ohm and Chung 2002). Wheat hardness is also reported to have a significant association with viscosity of water extractable arabinoxylans (Bettge and Morris 2000; Igrejas et al 2002a). Variation in proteins has been also considered as an important factor affecting wheat hardness and consequently cookie quality (Huebner and Gaines 1992; Ohm et al 1999, 2006; Giroux et al 2000). Although cookie dough mixing either does not or only minimally develops the gluten network, baking the dough leads to formation of a gluten network as dough temperature exceeds the glass transition point of the gluten proteins due to the increased unfolding, hydration, and aggregation of proteins (Doescher et al 1987; Gaines 1990). Gluten network formation during baking accompanies a decrease of water mobility and a drastic increase of dough viscosity that slows spread and eventually results in elastic shrinkage of the baking cookie dough, preventing the expansion of gas cells (Doescher et al 1987; Slade et al 1989; Miller and Hoseney 1997). Thus, desirable gluten properties for cookie making include weak network development with low elasticity/high extensibility, minimal oxidative gelation between proteins for low dough viscosity, and high glass transition temperature (Doescher et al 1987; Slade et al 1989; Pedersen et al 2004; Bettge and Morris 2007). These studies suggest that qualitative variations in flour protein affect cookie quality as well as the quantitative variations. Qualitative variations in the main gluten proteins such as high molecular weight glutenin subunits were reported to have significant associations with cookie quality among soft wheat cultivars (Souza et al 1994; Labuschagne and van Deventer 1995; Hou et al 1996a,b; Igrejas et al 2002a,b). Huebner et al (1999) also reported a negative correlation between soft wheat quality characteristics and the quantities of individual protein fractions of gliadin and reduced glutenin analyzed by sizeexclusion high performance liquid chromatography (SE-HPLC). Variations in molecular weight distributions of native flour proteins have routinely shown significant associations with wheat quality characteristics and so their inclusion in predictive algorithms has a strong potential to improve quality evaluations (Bangur et al 1997; Morel et al 2000; Ohm et al 2006, 2008). For example, Ohm et al (2006, 2008) demonstrated that quality characteristics have distinct associations with specific protein fractions separated according to molecular weight by presenting collective correlation coefficients estimated using absorbance area (AA) and area percentage data of SE-HPLC at 0.05-min retention time intervals across the whole elution profile. These results also suggested that SE-HPLC data from flour native proteins could be applied to develop prediction models of wheat quality characteristics by multivariate analysis methods (Ohm et al 2006, 2008). Despite significant associations of proteins with soft wheat quality characteristics (Souza et al 1994; Labuschagne and van Deventer 1995; Hou et al 1996a,b; Igrejas et al 2002a,b), no research has been conducted to investigate their relationships with variations in molecular weight distributions of whole-wheat proteins. This study was performed to investigate whether SE-HPLC chromatograms of whole-wheat protein extracts could be used for quality evaluations in wheat breeding programs and in industry. The use of whole wheat protein extract is expected to help greatly to evaluate wheat quality rapidly because the laborious and timeconsuming flour milling is not required. The specific objectives 1 USDA-ARS-RRVARC-NCSL, Cereal Crops Research Unit, Wheat Quality Lab, Fargo, ND. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by Department of Agriculture and does not imply its approval to the exclusion of other products that also may be suitable. 2 Corresponding author. E-mail: [email protected] 3 Dept. of Crop & Soil Science, Oregon State University, Corvallis, OR. 4 USDA-ARS, Western Wheat Quality Lab, Pullman, WA. doi:10.1094 / CCHEM-86-2-0197 This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. AACC International, Inc., 2009.