Effect of composition of glutenin subfractions on rheological properties of wheat

Gluten extracted from defatted flours of cv. Aubaine (extra-strong), Herewa rd (strong) and Riband (weak) was separated into five different fractions ( R2 to R6) by sequential centrifugation and addition of sodium chloride. A s even-minute mixing time was used to carry out fractionation on the basis of depolymerization of glutenin macropolymers (GMP). Depolymerization of GMP occurred at much higher rates in dough of the weak cultivar compared to the strong and extra-strong cultivars. Polypeptide compositions of different g lutenin fractions were determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis under reduced and non-reduced conditions, followed by d ensitometric scanning of stained patterns. The amount of HMW-glutenin subun its decreased and LMW-glutenin subunits increased correspondingly in each c ultivar with the fractionation from R-2 to R-6. The rheological behavior of the fi actions was analyzed by small deformation rheological tests (strain sweep and frequency tests). The high molecular weight fraction (R-2) from extra-strong wheat had a higher value of G' and a lower tan delta value as compared to strong and weak bread-making wheats. The moduli of HMW glutenin fractions (R2 and R3) were frequency independent and promoted the network properties, whereas moduli of LMW glutenin fractions were frequency depende nt and gave rise to a plasticizing effect. Therefore, it was concluded from the present studies that HMW-glutenin subunits are not the only factors go verning good bread-making quality but their proportions in relation to low molecular weight glutenin subunits is equally important in striking a balan ce between viscous and elastic properties essential for bread making perfor mance.