Structural Properties and Mechanical Durability of Extruded Fish Feed

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AbstractThis 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.Practical ApplicationsThe results indicate that a waiting time of more than ∼7 s will allow the extruded fish feed pellet to relax to its equilibrium state. This can be readily implemented in the texture profile analysis method to increase the response in correlations between structural properties and mechanical durability. The specific results presented in this article indicate that the viscoelastic behavior of the pellets should be controlled to increase mechanical durability. The realizations from this work will benefit future research aiming to promote mechanical durability of fish feed pellets in the drying process. The concept and findings will however find use in the assessment and promotion of mechanical durability for a much wider range of dry feed and food products.