Particle size distribution of raw materials plays an important role in extrusion process during direct expanded extrudates manufacturing. In most of the food industries all types of fl ours come in a production plant packed in bags with certain checkmarks that consist of average size of particles expressed in μm.
That particle size range is very relative, because mostly it means that size of most frequent particles is expressed. During extrusion processing of corn fl our and whey or soy proteins blends are interject, then it is very important to know precise particle size of the interjected blends. If it does not match, raw materials should be sieved and particular fractions separated.
To obtain the best fraction of corn fl our for extrusion processing (200 – 450 μm), sieving was conducted in shaker “Analysette 3” with sieving times of 5, 10 and 15 minutes. For each of these three measurements an agglomerate creation was spotted, followed by the major remain of the sample at the mesh of 450 μm. Sieving was repeated with aid of ultrasound (250 W), using power generator and by ultrasonic ring with transducer (“UIS 250 L”) mounted on the sieves. Sieving was conducted again with sieving times of 5, 10 and 15 minutes, and variable amplitude of works of 25, 50 and 75% for ultrasound. Within each of these nine measurements a partial or complete agglomerate breakdown was achieved, and an optimal fraction for extrusion processing was acquired. For the desirable particle size fraction in range of 200 – 450 μm for extrusion, under the conditions of 10 and 15 minutes of sieving time with amplitude work of 75%, the most of the sample remained within desirable range (83,79% and 83.4%).

ultrasound; sieving; extrusion; corn flour

Published by University of Zagreb, Faculty of Agriculture, Zagreb, CROATIA
Sponsored by Ministry Science and Education of the Republic of Croatia