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Title: VISCOSITY MODEL FOR AN EXTRUDED FISH FEED AS A FUNCTION OF PARTICLE SIZE

Author
item LAM, C. DESMOND - FM INSURANCE COMPANY
item Flores, Rolando

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary: Extrusion is an unit operation used extensively in food and feed processing. Its complexity is due to the combination of operations that affect the raw material in one processing step. Extrusion involves mixing, conveying, cooking, and forming. This study was undertaken to determine the impact of raw material particle size used in extrusion on the viscosity, or flow behavior, of the extrudate leaving the extruder. Viscosity is a factor that determines the energy used in the feed manufacturing. A mathematical algorithm was developed that describes and quantifies the effect of particle size and moisture on the extrudate viscosity. The material with lower moisture and larger particles increased the specific mechanical energy. Even though this study was done on a laboratory scale extruder, the viscosity model developed in this study can be applied to the development of large scale extrusion models that determine the effect of particle size on the feed material extrudates.

Technical Abstract: A model was developed for the influence of particle size on the extrusion of a biological material (fish feed). The study was conducted using factorial experiments in a fractional replication design for four variables with three levels, and one-third of the replicates (3 to the fourth power factorial in 27 units) were examined in a laboratory extruder. The torque- -screwed speed measurement was used to develop a viscosity model equation that considered different shear rates, product temperature, initial moisture content, and particle size. When particle size decreased, the apparent viscosity became smaller. The barrel pressure was important in producing extrudate with a uniform volume over the range of processing conditions tested, because it had a strong correlation with the volumetric expansion. The material with lower moisture and larger particles caused the specific mechanical energy to increase. The viscosity model developed in this study can be applied to the development of large scale extrusion models that determine the effect of particle size on the feed material extrudates.