DEVELOPMENT OF COMPOSITE STRUCTURES IN THE GELLAN POLYSACCHARIDE SUGAR SYSTEM/

A sensitive in-house rheometer and two measuring configurations were e mployed to examine the structural properties of gellan/sugar preparati ons at stoichiometric levels of added calcium ions. Perforated cylinde rs allowed recording of the gelation process in slippery gellan gels ( from 0 to 40% sucrose) whereas systems with greater amounts of co-solu te could also be analysed with a flat cone-and-plate geometry. The sha rp sigmoidal transition of the highly enthalpic aggregated helices in aqueous or low sucrose (up to 30%) gellan gels was observed at tempera tures below 60 degrees C upon cooling (1 degrees C/min). This gave way at 60% sucrose and beyond (high solids regime of sucrose plus corn sy rup) to a thermally stable structure with a low modulus monotonic temp erature profile (from 90 to 5 degrees C). At the intermediate range of co-solute (30 to 60%) a bimodal cooling profile was recorded which wa s rationalised on the basis of a composite network comprising lightly cross-linked and therefore flexible gellan chains, and rigid aggregate s. In the absence of external calcium, at the intermediate level of so lids, only the aggregated type of network was formed at the low temper ature end, apparently supported by the batch salts. Therefore, the add ed calcium facilitated stabilisation at the top temperature end of lim ited intermolecular associations between the thermally vibrant gellan chains in a sugar (>40%) environment. (C) 1997 Elsevier Science Ltd.