Plasticization effect of solubles in fishmeal

- Water soluble compounds in fishmeal influence glass and flow transition temperatures.
- Water solubles and moisture have additive effects with no interaction.
- A higher plasticization effect of solubles addition compared to moisture on a molar basis
- Glass transition temperature in fishmeal 50-60 °C lower than in casein and plant proteins
- Plasticization effect of solubles can be attributed to low molecular N-compounds.

The influence on glass transition (TgMid) and flow-starting (Tf) temperatures of water soluble dry matter (WSDM) in fishmeal has been assessed combined with moisture content by use of a central composite design and response surface modeling. Established models with R2 > 0.951 showed significant additive effects of WSDM and moisture on TgMid and Tf without interaction. The effect of WSDM on TgMid could also be modeled based on the Gordon-Taylor equation. The main effects on TgMid and Tf were 3.1 and 1.2 times higher, respectively, for each percent increase in moisture compared to WSDM. However, on a molar basis the effect of solubles addition will be higher compared to moisture. The plasticization effect can be attributed to the content of low molecular N-compounds and also influences the viscosity reduction of temperature increase in the rubbery phase. Fishmeal has a lower TgMid compared to casein and plant proteins. Combined, the observed physicochemical properties might contribute to explain reported unique functional properties of fishmeal with positive impact on physical pellet quality and open up the possibility to obtain a satisfactory thermomechanical transformation in the extrusion process at reduced moisture level.