Molecular and pasting properties of some wheat starches

Molecular structures and pasting properties of starches from four wheat varieties, (Egret and Rosella, soft grain; Vasco and Halberd, hard grain) were characterized and the relationships between pasting and molecular properties were analyzed. The starches (10%, w/w) showed pasting temperatures in the range of 63.4-67.6 degrees C, maximum viscosities (V-max) 201-323 RVU, breakdown 54-176 RVU, and consistency 118-198 RVU measured by a Rapid Visco Analyzer. The strong positive correlations have been found between the V-max by RVA (10%) and number- (<(DP)over bar (n)>) and weight-average DP (<(DP)over bar (w)>) of amyloses and <(DP)over bar (n)> of amylopectins. V-max = 0.425 .<(DP)over bar (n)> (amylose)-315 (r = 0.989). 0.303 = <(DP)over bar (w)> (amylose)-953 (r = 0.998) and V-max = 0.0234 .<(DP)over bar (n)> (amylopectin)-116 (r = 0.912). The breakdown showed a good positive correlation to V-max. The amylopectins of the high viscosity (HV) starches (Rosella and Halberd) gave lower values of iodine affinities and comprised a lower amount (2% of total) of extra long chains (ELC, weight-average CL > 500) than those (3 or 4%) of the low viscosity (LV) starches (Vasco and Egret). It has been suggested that the high molecular weights of amylose and amylopectin and probably low amounts of ELC of amylopectin increase the viscosity of wheat starches on pasting. Copyright (C) 1996 Elsevier Science Limited.