Impact of fish protein concentrate on apparent viscosity and physical properties of soy protein concentrate subjected to thermomechanical treatment

Rafiq Ahmad,Åge Oterhals,Ying Xue,Tore Skodvin,Tor Andreas Samuelsen

doi:10.1016/j.jfoodeng.2019.04.014

Rafiq Ahmad, Åge Oterhals + Show 3 more

Open Access

https://doi.org/10.1016/j.jfoodeng.2019.04.014

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Abstract

The aim of this research was to investigate the plasticizing and binding effect of fish protein concentrate (FPC) on soy protein concentrate (SPC) with the use of a capillary rheometer with pre-shearing capabilities. A 3-component mixture design was used to study the effect of the variables SPC, FPC and water. Mixture models with R2 in the range of 0.703–0.998 (P < 0.01) were established for apparent viscosity, extrudate hardness and expansion parameters of the plasticized materials. Extrudate microstructure as porosity, pore size distribution, cell wall thickness and distribution, were measured with the use of X-ray microtomography and models established with R2 in the range of 0.582–0.941 (P < 0.02). The mixture components affected apparent viscosity with the highest value observed for the blend with maximum SPC concentration (1381.6 Pa s) followed by maximum FPC concentration (858.6 Pa s), and lowest for the blend with maximum water concentration (398.0 Pa s). Lowest pellet hardness (136.2 N), density (904.3 kg/m3) and highest expansion (1.44) were found for the blend with maximum SPC concentration and can be attributed to incomplete thermomechanical transformation. Extrudate physical properties and expansion were explained by the extrudate microstructure. FPC added at a concentration of 65–70 g/kg gave values of hardness, extrudate density and microstructure similar to SPC added 100 g/kg of water, confirming the potential for the use of FPC as plasticizer and binder in the fish feed extrusion process.

Highlights

The fish feed extrusion process is a thermomechanical process that transforms the feed ingredients into a plasticized and high viscous flowable material that is shaped through dies, cut into pellets, dried and added oil in a vacuum coating operation
The RheoArt measurements were performed under standardized conditions and the soy protein concentrate (SPC) blend plasticized with fish protein concentrate (FPC) gave different extrudate properties compared to water plasticization
FPC added at a concentration of 65–70 g fat free dry matter (FFDM)/kg gave values of hardness, extrudate density, open and total porosity, surface to volume (SV) ratio and connectivity density similar to SPC added 100 g/kg of water

Summary

Introduction

The fish feed extrusion process is a thermomechanical process that transforms the feed ingredients into a plasticized and high viscous flowable material that is shaped through dies, cut into pellets, dried and added oil in a vacuum coating operation. The use of fishmeal in salmon feed formulations has been reduced from 65% to 18% in the last two decades and has partly been replaced by alternative plant-based ingredients as soy protein concentrate (SPC), vital wheat gluten (WG) and sunflower meal (SFM). WG has high protein content (> 80%), an unbalanced amino acid profile and reduced oil adsorption, caused by change in pellet microstructure, restrict the use. SPC is the dominant plant protein ingredient, replacing approximate 21% of the fishmeal This is possible due to its high protein content, balanced amino acid profile and low carbohydrate and fiber

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