EVALUATION OF THE IMPACT OF ANNEALING ON GELATINIZATION AT INTERMEDIATE WATER-CONTENT OF WHEAT AND POTATO STARCHES - A DIFFERENTIAL SCANNING CALORIMETRY AND SMALL-ANGLE X-RAY-SCATTERING STUDY

The DSC (differential scanning calorimetry) thermograms of wheat and p otato starches at 50% (w/w) wa.ter content are characterised by two ge latinisation endotherms, Two separate phenomena coinciding with the tw o DSC endotherms can be distinguished in the SAXS patterns of 50% (w/w ) suspensions of wheat and potato starches during heating from 25 to 9 5 degrees C at 2 degrees C/min: an increase in peak integral in the te mperature domain of the first (G) endotherm and a marked decrease in p eak integral in the temperature domain of the second (M1) endotherm, O ne- and two-step annealing affect only the G endotherm, leading to a s hift to a higher temperature of up to 8 degrees C, sharpening of the p eak and an increase in enthalpy, while the completion temperature of t he M1 endotherm remains unchanged, Static SAXS measurements indicate t hat the repeat distances of crystalline and amorphous lamellae in whea t (105 Angstrom) and potato (99 Angstrom) starch granules are unaffect ed by annealing, One- and two-step annealing intensify the SAXS peaks, The most striking difference between the SAXS gelatinisation profiles of native and annealed starches is that there is no increase in peak integral at the onset of gelatinisation of annealed starches, The effe cts following annealing are interpreted as a decreased water absorptio n during gelatinisation. Annealing leads to a retardation of the initi al swelling and cooperative melting of the granules, without altering the stability of the most perfect crystallites. (C) 1998 Elsevier Scie nce Ltd. All rights reserved.