Published in Cereal Chemistry: 88(1): 41-44, 2011
Kernel elastic properties and sedimentation: influence of high and low molecular weight glutenin allelic composition.
Figueroa, J.D.C.; Peña, R.J.; Maucher, T.; Rayas-Duarte, P.; Khan, K.
The suitability of wheat for breadmaking is determined to a large extent by the properties of the major storage proteins. The wheat storage proteins are classified into two groups, glutenin and gliadin, based on extraction and solubility of the Osborne method (Shewry et al 1986). In general, glutenin imparts elasticity to the bread dough, whereas gliadin is viscous and gives extensibility (Payne et al 1984; Shewry et al 1986). When glutenin is treated with a reducing agent such as mercaptoethanol, it dissociates into several subunits that were classified into HMW and LMW (Payne et al 1984). A close relationship between the LMW subunits and gliadins was indicated by several studies (Shewry et al 1986; Jood et al 2000). The presence of certain HMW subunits of glutenin was significantly associated with several quality tests (Payne et al 1981, 1987; Luo et al 2001; Zhu and Khan 2002; Tohver 2007). HMW subunits also occur in allelic variants that differ in mobility on SDS-PAGE. Payne et al (1981, 1987) have shown that breadmaking quality is particularly associated with variation at the Glu- D1 and Glu-A1 loci. In the Glu-D1 locus, good quality is specifically associated with the 5+10 pair of subunits (Payne et al 1981; Luo et al 2001) compared with the poor quality allelic subunits 2+12, suggesting differences in amino acid sequences that could affect the structure and physical properties of gluten (Halford et al 1992). Another two allelic subunits encoded by the Glu-A1 locus that occur in bread wheats are A1-1 and Al-2*. Payne et al (1979, 1980, 1981) initially showed that subunits A1-1 and A1-2* were correlated with good quality when compared with the null (silent) allele, using SDS-sedimentation as an indirect measurement of breadmaking quality. It is generally agreed that HMW-GS alone are insufficient to account for differences in quality and LMW-GS must also be taken into consideration (Luo et al 2001; Flæte and Uhlen 2003). However, the total effect of Glu-1 loci is relatively larger than that of Glu-3 loci (Gupta and MacRitchie 1994; Luo et al 2001). The selection for LMW-GS is not commonly used in wheat breeding programs because it requires specific technical expertise to properly separate and identify individual alleles (Flæte and Uhlen 2003). While a substantial amount of research has been dedicated to establishing the relationship between HMW-GS composition and important dough viscoelastic properties and breadmaking quality, very limited work has been dedicated to examining basic mechanical properties as related to elastic properties of wheat kernels (Ponce-García et al 2008). This study will address the basic mechanical and viscoelastic properties of wheat kernels by measuring the elasticity of the wheat directly from intact kernels and analyzing its relationship to sedimentation volume (as a rough measurement of the baking strength) and glutenin allelic composition. The objective of this study was to evaluate individual alleles of HMW and LMW glutenin subunits in a set of 26 bread wheat samples and their possible influence on the elastic properties of intact wheat kernels and sedimentation volumes.
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