Effect of particle size and temperature on rheological, thermal, and structural properties of pumpkin flour dispersion

Controlling the rheological properties of dispersion has been of great interest in the food processing industry. Effects of particle size and temperature on oscillatory rheology of pumpkin flour dispersion were studied. Fresh pumpkin was freeze-dried, grinded and sieved through selected screens to obtain desired particle size fractions (74-841 mu m). Most of the particles are spherical in shape. The glass transition temperature (T-g) and the melting temperature (T-m) of starch-lipid complex varied with particle size which is believed to be due to compositional variations. Rheological measurement of reconstituted particles as a function of temperature (10-90 degrees C) and concentration (4-10% w/w) indicated a solid-like behavior (G' > G ''). Sediment volume fraction (phi) of isolated particle dispersions indicated a gradual decrease with decrease in particle size, which directly influences the mechanical strength and visco-elasticity of the dispersion. Particle size influenced the mechanical rigidity of pumpkin dispersion markedly whereas the temperature had the least effect. An unexpected increase in G' of finest particle containing dispersion with temperature could be associated with gelatinization of starch and flocculation of particles with broken cell walls. Microscopic observation revealed the presence of a continuous network for the finest particle dispersion, as opposed to discontinuous one for other particle sizes. (C) 2013 Elsevier Ltd. All rights reserved.