The effect of extrusion temperature and drying-tempering on both the kinetics of hydration and the textural changes in extruded ready-to-eat breakfast cereals during soaking in semi-skimmed milk

Ready-to-eat breakfast cereals were made by a two-step extrusion-cooking and toasting process. Before toasting the products were given a drying-tempering step. Two process variables (extrusion temperature and moisture content before toasting) were manipulated in order to obtain products with different physical characteristics. Density, hardness, hydration kinetics and textural changes of the products during soaking were studied in order to analyse the influence of these variables on the product quality. Both the variables significantly affected the product quality indices such as hardness and density. The processing conditions had only a slight influence on product water uptake during hydration but a dramatic influence on product softening. The hydration and softening rates were negatively correlated with density. When density was equal samples extruded at different extrusion temperatures showed different water uptake and softening rates. Products with the same values of initial hydration rate showed different initial softening rates because of extrusion temperature.