Effect of glutenin subfractions on bread-making quality of wheat

Five glutenin subfractions (R-2-R-6) were extracted by sequential centrifug ation and addition of sodium chloride, from defatted flours of three wheat cultivars viz. Aubaine (extra-strong), Hereward (strong) and Riband (weak). Seven minutes mixing time was used to carry out fractionation on the basis of depolymerization of glutenin macropolymers (GMP) by using a 2-g Mixogra ph traces. Depolymerization of GMP occurred at much higher rates in dough o f weak cultivars compared with strong and extra-strong cultivars. Protein c ontent was also estimated in GMP (SDS-unextractable) and supernatant (SDS-e xtractable). Extra-strong cv. Aubaine contained maximum amount of all the g lutenin fractions (R-2-R-6) followed by strong cv. Hereward and weak cv. Ri band. Polypeptide compositions of different glutenin fractions were determi ned by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE ) under reduced and unreduced conditions, followed by densitometric scannin g of stained patterns. The pattern areas of reduced fractions were divided into subareas representative of three main protein classes: high molecular weight (HMW) glutenin subunits; omega -gliadins and a mixture of low molecu lar (LMW) glutenin subunits and alpha, beta and gamma -gliadins. The amount s of various subunits were proportionate according to the molecular weight of the fractions in each cultivar. The ratio of HMW-glutenin subunits to th e LMW-glutenin subunits in each cultivar were found to decrease with the fr actionation from R-2 to R-6. Bread-making quality of three cultivars was al so assessed by adding various fractions to a base flour and measuring mixog raph peak development time and loaf volume in an optimized baking test. The quality of bread prepared from flour of weak cv. Riband was improved signi ficantly by the addition of HMW fraction (R-2) when measured in terms of lo af volume. However, the addition of LMW fraction (R-5 + R-6) did not cause any appreciable improvement in bread quality over control. On the other han d, addition of HMW fraction (R-2) in the flour of good bread wheat cv. Here ward caused adverse effects on the bread-making quality by disturbing the v iscoelastic properties. Supplementation of R-2 fractions in extra strong wh eat cv. Aubaine caused marginal reduction in loaf volume over control. Ther efore, the precise proportion present of the two classes of subunit is esse ntial to achieving a proper balance between elastic and viscous properties.