EFFECT of PHYSICAL STRUCTURE of STARCH MATERIALS ON WATER DIFFUSIVITY

The physical structure, developed during drying, affects the transport of water and the quality of processed solid foods. the effective diffusivity of water in starch-based systems was estimated from drying data at moisture 3–50% and temperatures 40-100°C. Hydrated granular or gelatinized starches and their mixtures with sugars or inert particles were used to produce different structures during air drying. the physical structure was characterized by the bulk porosity, estimated from the bulk and solid densities of the samples. the water diffusivity was influenced strongly by the porosity, developed during drying. Mechanical compression, starch gelatinization or addition of water-soluble sugars reduced the water diffusivity in granular starches. Incorporation of inert particles or extrusion cooking resulted in higher water diffusivities, due to higher porosities of the starch/inert mixtures or the expanded extrudates.