Molecular Weight Distribution of Proteins in Hard Red Spring Wheat: Relationship to Quality Parameters and Intrasample Uniformity

Cereal Chem. 87(6):553–560 Molecular weight distribution (MWD) of proteins extracted from hard red spring wheat was analyzed by size-exclusion HPLC to investigate associations with wheat and breadmaking quality characteristics. Certain protein fractions were related to associations between wheat and breadmaking parameters, specifically when effect of quantitative variation of protein on those parameters was statistically eliminated by partial correlation analysis. SDS-unextractable high molecular weight polymeric proteins had positive partial correlations with percent vitreous kernel content and breadmaking parameters, including mix time and bread loaf volume. SDS-extractable protein fractions that were eluted before the primary gliadin peak had positive partial correlations with kernel hardness and water absorption parameters. The proportion of main gliadin fractions in total protein had a negative partial correlation with bread loaf volume and positive correlations with kernel hardness and water absorption parameters. Intrasample uniformity in protein MWD and kernel characteristics was estimated from three kernel subsamples that were separated according to single kernel protein content within individual wheat samples by a single-kernel near-infrared sorter. Wheat subsamples were significantly different in protein MWD. Intrasample uniformity in protein MWD did not differ greatly among wheat samples. Size-exclusion high-performance liquid chromatography (SEHPLC) has been applied to separate proteins according to protein molecular weight distribution (MWD) (Bietz et al 1984; Batey et al 1991). Research using SE-HPLC indicated that SDS-unextractable polymeric proteins could enhance dough strength while extractable polymeric proteins were associated with weak dough characteristics (Gupta et al 1993; Ciaffi et al 1996; Bangur et al 1997; Borneo and Khan 1999; Morel et al 2000; Tsilo et al 2010). Bean et al (1998) and Park et al (2006) reported similar results showing that mix peak time had a positive association with propanolinsoluble proteins and a negative association with propanol soluble proteins. Ohm et al (2006, 2008, 2009a) researched the association more specifically by calculating the correlation of quality parameters with SE-HPLC absorbance values measured at a narrow interval of retention time. They reported that specific protein fractions had distinct effects on quality characteristics, specifically that SDS-unextractable high molecular weight polymeric proteins had greater positive correlations with dough characteristics than other polymeric protein fractions. Tsilo et al (2010) reported similar findings using hard spring recombinant inbred lines. Variation in proteins was also associated with wheat kernel characteristics such as kernel hardness (Huebner and Gaines 1992; Ohm et al 1998; Ohm and Chung 1999; Giroux et al 2000; Ohm et al 2006) and vitreousness (Dexter et al 1989; Gianibelli et al 1991; Samson et al 2005). Specifically, Huebner and Gaines (1992) found that specific fractions of gliadins had significant correlations with average particle size of ground wheat flour. Ohm et al (2009a) also reported that protein fractions rich in gliadins affected the variations of kernel hardness in soft winter wheat. Few reports have been published on associations of protein MWD and wheat characteristics in hard red spring wheat despite significant correlation found in other wheat classes. In the wheat marketing system, consistency in quality characteristics is a very important element for wheat procurement (Wilson and Dahl 2008). To ensure consistency in quality, the U.S. wheat industry is moving toward a system that requires the segregation of wheat of which identity is preserved by specifying variety, growing location, and quality characteristics (Wilson and Dahl 2008). Production of wheat with uniform distribution of quality characteristics among individual kernels is expected to enhance segregation of wheat according to quality standards and, consequently, promote consistency of wheat quality through identity preservation in commercial production and marketing systems. Automated single-kernel near-infrared (SKNIR) technology has been successfully applied to determine the uniformity of distribution of quality characteristics in a wheat sample such as intravarietal variation of kernel protein content (Bramble et al 2006). Recently, uncertainty of consistency is specifically pointed out as a problem in wheat trading for mixing and breadbaking characteristics because of the requirements for large sample amounts and time-consuming and costly evaluation procedures (Wilson and Dahl 2008). Because protein MWD has significant associations with dough mixing and breadmaking characteristics (Singh et al 1990b; Batey et al 1991; Larroque et al 2000; Morel et al 2000; Tsilo et al 2010), the analysis of protein in whole grain by SE-HPLC could be effective in gaining information on uniformity or consistency of mixing and breadbaking characteristics in hard red spring wheat samples. However, in previous studies by Ohm et al (2008, 2009a,b), protein extracted from whole grains of hard red spring wheat had not been analyzed by SE-HPLC to detail its associations with quality characteristics. The objectives of this study were to investigate associations of wheat and breadmaking quality characteristics with MWD of proteins in whole grain and to evaluate intrasample uniformity of protein MWD and kernel characteristics in hard red spring wheat. Specifically, the focus of this investigation was on determining whether SE-HPLC analysis of proteins extracted from whole wheat grain could be employed to further evaluate quality characteristics and consistency in hard spring wheat. MATERIALS AND METHODS Twenty wheat samples consisted of 10 hard red spring wheat cultivars each harvested in North Dakota at two locations in 2006. Single kernel characteristics were measured with a Single Kernel Characterization System (SKCS) model 4100 (Perten Instruments, Huddinge, Sweden) according to the Approved Method 55-31.01 1 USDA-ARS-RRVARC-NCSL, Cereal Crops Research Unit, Hard Spring & Durum Wheat Quality Laboratory, Fargo ND. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable. 2 Corresponding author. Phone: 701-239-1414. Fax: 701-239-1377. E-mail address: [email protected] 3 Department of Plant Sciences, North Dakota State University, Fargo, ND. 4 USDA-ARS-CGAHR, Grain Quality & Structure Research Unit, Hard Winter Wheat Quality Laboratory, Manhattan, KS. 5 USDA-ARS-CGAHR, Engineering & Wind Erosion Research Unit, Manhattan, KS. doi:10.1094 / CCHEM-06-10-0088 This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. AACC International, Inc., 2010.