Structural Properties and Mechanical Durability of Extruded Fish Feed

This article investigates the possible correlation between mechanical properties of
fish feed pellets and their mechanical durability. Mechanical properties were
obtained by texture profile analysis (TPA) and stress relaxation test (SRT) of different
types of fish feed. The results were correlated against a conventional test of
mechanical durability (DORIS, Durability On a Realistic, test). From SRT it was
found that for achieving a high durability, pellets should be able to relax an
applied force nonelastically. From TPA, it was found that a durable pellet should
also be able to return its original state after a deformation. By fitting SRT data
with a two time constant generalized Maxwell model, it was found that the largest
time constant is ∼7 s. The waiting time in-between the two impacts in TPA was
increased from 5 to 15 s, which significantly improved the correlations against
mechanical durability.