Spray drying thermoplastic starch formulations: Need for processing aids and plasticizers?

Retrogradation of amorphous thermoplastic starch (TPS) films obtained by compression moulding of spray dried amorphous powder was investigated. The aim of the work was to study the influence of malto-oligosaccharide molecular weight, i.e. dextrose equivalents (DEs), on the performance of the powders and the films. Amorphous TPS films were obtained, irrespective of the additive used. At a relative humidity (RH) of 0% and 50% all samples maintained their amorphous nature while at RH100% retrogradation was suppressed for all formulated starch films. It is shown that the rate of moisture uptake, and as a consequence, the rate of retrogradation, depends on the molecular weight of the additive. FT-IR and TGA measurements proved a more effective interaction of starch with low molecular weight additives such as maltose and glucose syrup (DE 38.2) than for the higher molecular weight maltodextrine (DE 19.1).