Water‐soluble protein level in fishmeal affects extrusion behaviour, phase transitions and physical quality of feed

• Published in: Aquaculture nutrition Vol. 22; no. 1; pp. 120 - 133
• Main Authors: Samuelsen, T. A, Oterhals, Å
• Format: Journal Article
• Language: English
• Published: Oxford Blackwell Science 01.02.2016; Blackwell Publishing Ltd; Hindawi Limited
• Subjects: adsorption; blue whiting; bulk density; drying; energy; extrusion; feed industry; feed quality; fish feed; fish feeds; fish meal; flow-starting temperature; glass transition temperature; hardness; oils; plasticizer; plasticizers; regression analysis; response surface methodology; steam; temperature; water content
• ISSN: 1353-5773; 1365-2095
• DOI: 10.1111/anu.12235

The aim of this research was to investigate the effect of water‐soluble protein (WSP) as a plasticizer in the fish feed extrusion process and the impact on physical pellet quality. A three‐factor central composite design was used to study the influence of the variables WSP in the feed mix, and steam and water addition in the extruder. Regression models with r² in the range of 0.862–0.976 (P < 0.001) were established for specific mechanical energy (SME), pellet hardness, cutting strength, sectional expansion index, length, bulk density, oil adsorption capacity and extrudate flow‐starting temperature (Tf). Addition of WSP had a positive effect on SME and improved the physical pellet quality, while moisture had the opposite effect. Expansion parameters showed a complex relationship and were influenced by all the studied process variables. Increase in WSP and moisture content had a comparable effect on Tf reduction. This opens up the possibility to obtain a satisfactory ‘cook’ at reduced moisture level with a potential for significant reduction of the energy consumption during drying of the extrudate. Overall conclusion from the experiment is that WSP can be used as a processing aid for the fish feed industry, serving multiple purposes as nutrient, plasticizer and binder in extruded fish feed.