Effect of temperature on the synthesis, composition and physical properties of potato starch

Potato tubers (cv Maris Piper) were grown at 10, 16, 20 and 25 degrees C in constant-environment chambers until maturity, whereupon the starches were extracted and subjected to rigorous chemical and physical analysis. The str ucture of the amylopectin molecules from the different starches post-debran ching with isoamylase showed very little variation. The amylose and phospho rus content of the starches did show some variability while granule size te nded to decrease as growth temperature was increased. There was, however, a marked increase in gelatinisation temperatures with a roughly constant ent halpy of gelatinisation as a function of growth temperature. The number of amylopectin double helices was determined by C-13 CP/MAS-NMR and crystallin ity by wide-angle X-ray diffraction and in common with the enthalpy of gela tinisation found to be almost constant. It is proposed that the differences in the gelatinisation temperatures reflect enhanced registration of the am ylopectin double helices in crystallites which restricts hydration and henc e elevates gelatinisation temperatures. This is probably associated with en hanced rigidity of amorphous regions. The consequence of these ordering eff ects is that swelling is restricted, even if there is no detectable order b y DSC (post-T-c), because of steric hindrance to hydration exerted by the c loser proximity/improved registration of the amylopectin chains. (C) 1999 S ociety of Chemical Industry.