MOLECULAR AND PASTING PROPERTIES OF SOME WHEAT STARCHES

Molecular structures and pasting properties of starches from four whea t varieties, (Egret and Rosella, soft grain; Vasco and Halberd, hard g rain) were characterized and the relationships between pasting and mol ecular properties were analyzed. The starches (10%, w/w) showed pastin g temperatures in the range of 63.4-67.6 degrees C, maximum viscositie s (V-max) 201-323 RVU, breakdown 54-176 RVU, and consistency 118-198 R VU measured by a Rapid Visco Analyzer. The strong positive correlation s have been found between the V-max by RVA (10%) and number- (<(DP)ove r 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 Halb erd) gave lower values of iodine affinities and comprised a lower amou nt (2% of total) of extra long chains (ELC, weight-average CL > 500) t han those (3 or 4%) of the low viscosity (LV) starches (Vasco and Egre t). It has been suggested that the high molecular weights of amylose a nd amylopectin and probably low amounts of ELC of amylopectin increase the viscosity of wheat starches on pasting. Copyright (C) 1996 Elsevi er Science Limited.