Preparation and chemical characterisation of glutenin macropolymer (GMP) gel

• An optimized method to isolate glutenin macropolymer (GMP) gel is presented.
• Specific washing steps increase the polymer content.
• GMP gel contains protein, starch, water, and sodium dodecylsulphate.
• GMP gel is enriched in HMW glutenin subunits as compared to glutenin.
• Amount and composition of GMP gel are affected by wheat cultivar.

Glutenin macropolymer (GMP) is the SDS-insoluble subfraction of wheat gluten and one of the largest protein-based biopolymers in nature. Its amount in flours is strongly correlated with dough and bread quality. The aim of the present work was to optimise the preparation and to characterise the chemical composition of GMP. The best conditions for preparation were extraction of defatted flour with non-buffered 1.5% SDS solution, ultracentrifugation at 80,000 g, scraping off the gel layer, washing the gel with 60% ethanol and water, and freeze-drying. Dried GMP gels of two wheat cultivars (Akteur (AKT), Winnetou (WIN)) with high and poor baking qualities and different compositions of high-molecular-weight glutenin subunits were analysed and they contained starch (AKT, 50%; WIN, 72%), crude protein (35%; 8%), SDS (5%; 16%), and water (8%; 2%). The flours contained 36 and 6 mg/g (AKT; WIN) of GMP proteins. Proteins consisted of glutenins (90%) with a ratio of low-molecular-weight subunits to high-molecular-weight subunits of 1.7 (AKT) and 1.3 (WIN). The gliadin content was 10% and albumins/globulins were absent. In summary, the results revealed a detailed composition of GMP gels and confirmed data from literature that the amount of GMP protein is influenced by cultivar and glutenin subunit composition.