Wheat glutenin subunits in relation to baking quality parameters

Abstract

Wheat gluten has unique properties that make it suitable for bread-making. As a result bread-making quality is closely associated with gluten quantity and quality. This research was conducted to look at the relationship between varieties, environment, wheat glutens and potential bread-making quality. Specifically the objectives were: 1) to assess the environmental effect on the quantities of gluten and its subunits across a range of genotypes (both high and low molecular weight glutenins); 2) to quantify the relationships among glutenin subunits (both high molecular weight and low molecular weight) and baking quality parameters, and the relationships among those quality parameters themselves; 3) to quantify specific allelic (Glu-l & Glu-3) effects on bread-making quality and interpret the effects using genetic expression models.

Two sets of materials, a GXE trial and a set of recombinant lines were created. Fourteen New Zealand cultivars or lines with various baking quality were chosen for GXE trial and these were given six treatments that varied in fertiliser type (nitrogen or sulphate) and application time (early or late application). Based on the allele information, five recombinant lines were chosen for later analyses and quality tests. The quality tests were: wholemeal flour protein, white flour protein, hardness, SDS sedimentation volume, Pelshenke time and 10-gram mixograph.

The data obtained indicated that bread-making quality could be improved by late nitrogen application. Cultivars' responses to the environmental changes varied, they could be either stable or more responsive. Higher SDS sedimentation and mid-line peak values of the mixograph were mainly related to higher protein content. Pelshenke time values were mainly related to high molecular weight glutenin subunit score, which represents their qualitative or allelic differences.

Allelic differences were shown to significantly affect quality parameters. Possession of the null allele of Glu-A1 resulted in inferior values for most of the flour quality tests when compared to alleles 2* and 1. Possession of allele 5+10 for Glu-D3 was significantly related to longer Pelshenke times and greater SDS sedimentation volumes. Possession of different GluA3 alleles significantly affected wholemeal flour protein content, sedimentation volumes and mid-line peak values of the mixograph. Possession of allele d for Glu-A3 could be a valuable high quality predictor in breeding programmes.

Bread-making quality is a complex matter influenced by many factors apart from glutenins. This thesis has demonstrated a combined genetic and agronomic approach to wheat quality improvement. However, there remains substantial scope for further research in this area.