Optimal process water supplementation and ratio between corn gluten meal and soy protein concentrate to secure good physical pellet quality and minimize energy use during extrusion processing of fish feed

Abstract

The objective of this experiment was to find out which combination of water/steam addition and plant protein ingredient mix that gives best physical quality and process economy. The design was, however, restrained by a demand to reach a specified bulk density, above 420 g/l, set in order to meet requirements for high oil absorption capacity and fast sinking pellets. The moisture come from three sources: steam in the conditioner, water in the conditioner and water in the extruder. Total process water supplementation was 28%, 33%, and 39% for each of 4 combinations (0-300 g/kg) of corn gluten meal (CGM) and soy protein concentrate (SPC). However, water and steam addition was done by free combination of the three sources, to meet the bulk density criterion. This may have reduced the possibility to conclude concerning the main effects of water supplementation and optimal ratio between CGM and SPC.

Holmen durability analyzes showed that PDI value was in range from 99.2 to 99.7%. High pellet density in range from 720-784 g/l was reflected on sinking percentage values were almost all diets had 100% score. Sinking speed was in range from 8.2 to 13.2 m/s. Reduction in SME was found in diets where CGM content increases from 10 to 30%. The results obtained in this study indicate that CGM and SPC have comparable effects on physical pellet quality and energy use in extrusion, and thereby process economy.