EFFECT OF TEMPERATURE ON THE SYNTHESIS, COMPOSITION AND PHYSICAL-PROPERTIES OF POTATO MICROTUBER STARCH

Potato microtubers (cv Maris Piper) were grown at 10, 16 and 24 degree s C in total darkness; for 28 days. Soluble and insoluble starch synth ase, ADPglucose pyrophosphorylase, sucrose synthase and fructokinase w ere assayed in extracts of the microtubers and, in the case of soluble and insoluble starch synthase, activity was found to be particularly sensitive to increasing growth temperature. The starch content of the microtubers increased slightly with increasing growth temperature, I,u t with little effect on the number of granules per microtuber and a sm all increase in the average granule size. The microtuber starch granul es were much smaller than those found in commercial potato starch (c 8 -9 mu m modal diameter compared to c 21 mu m). Although the amylose co ntent of the microtuber starches tended to increase with increasing gr owth temperature, the phosphorus content was variable. Gel permeation chromatographic elution profiles of native and debranched microtuber a nd a commercial potato starch showed that no differences could be dete cted in either amylose or amylopectin molecular size, polydispersity o r unit chain distribution of amylopectin (which contained two major un it chain fractions at DP 21 and 56). The onset, peak and conclusion te mperatures of the DSC gelatinisation endotherm increased linearly as a function of growth temperature whilst the enthalpy of gelatinisation decreased. It is suggested that elevated temperature during starch bio synthesis facilitates ordering of amylopectin double helices into crys talline domains. (C) 1998 SCI.