Influence of screw configuration and screw speed on radial expansion and oil absorption capacity of extruded feed for Atlantic salmon
2016
Banjac, Vojislav (Institute of Food Technology, Novi Sad (Serbia)) | Čolović, Radmilo (Institute of Food Technology, Novi Sad (Serbia)) | Vukmirović, Đuro (Institute of Food Technology, Novi Sad (Serbia)) | Čolović, Dušica (Institute of Food Technology, Novi Sad (Serbia)) | Spasevki, Nedeljka (Institute of Food Technology, Novi Sad (Serbia)) | Đuragić, Olivera (Institute of Food Technology, Novi Sad (Serbia)) | Lević, Jovanka (Institute of Food Technology, Novi Sad (Serbia))
High quality fish feed is mainly produced by extrusion process. Expansion level and oil absorption capacity are important characteristics of extruded pellets for salmonides, since salmonides require high energy diets provided by high fat content that is achieved by addition of oil using vacuum coating system in pellets after extrusion process. Expansion also directly affects bulk density, feed property that needs to be adjusted according to the feeding habits of the target species. In this study commercial diet for Atlantic salmon was extruded by seven section twin-screw extruder. For promoting expansion two different screw configurations were used while screw speed was progressively increased, set at 350, 700 and 750 RPM. Temperatures in third and sixth section of the extruder barrel, die temperature, die pressure and specific mechanical energy were monitored and recorded during extrusion. Bulk density, radial expansion and maximum oil absorption capacity of extruded feed were determined. Increase of screw speed lead to the increase of specific mechanical energy and die temperature during extrusion, with negligible change in the die pressure for both used configuration. Bulk density of feed was significantly (p<0.05) decreased while expansion and oil absorption capacity significantly increased (p<0.05) as the screw speed was increased. There were no significant differences in bulk density, expansion ratio and oil absorption capacity for samples produced at 700 RPM by two different screw configurations.
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