Structural and textural properties of rice-carrot extruded products
2012
Oikonomopoulou, Vasiliki P. (National Technical University of Athens, Athens (Greece). Department of Chemical Engineering) | Krokida, Magdalini K. (National Technical University of Athens, Athens (Greece). Department of Chemical Engineering)
Extrusion cooking is used in the food industry, to produce direct expanded snacks; the nutritional value of these extruded snacks usually increases with the addition of high-value food ingredients. The objective of the present study was the determination of the effect of process conditions on the structural and textural properties of rice extrudates enriched with carrot. Extrudates were prepared using a twin-screw extruder, operated at different conditions, including screw speed (150-250 rpm), extrusion temperature (140-180 ºC), feed moisture content (14-20%) and carrot-rice flour ratio (5-10%). True density of the products was measured using a helium stereo-pycnometer and apparent density was obtained by measuring their dimensions with a caliper. The expansion ratio was determined as the ratio of the diameters of the extrudates to the die. The textural properties (maximum stress, maximum strain and elasticity modulus) of extruded products were obtained using a universal testing machine. A stereomicroscope was used in order to visualize the macrostructure of selected extrudates. Simple mathematical models were used in order to correlate the examined properties with the extrusion conditions. Apparent density increased with moisture content and material ratio and decreased with temperature and screw speed, while porosity presented the opposite trend. Expansion decreased with moisture content, material ratio and temperature, while a screw speed rise increased the expansion. Moisture content and extrusion temperature affected positively the textural properties. The increment of carrot concentration led to the increment of maximum stress and elasticity modulus and the decrement of maximum strain, whereas screw speed caused opposite trend.
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