The aim of this research is to evaluate the impact of various process conditions on the physical properties and digestibility of extruded fish feed at different barrel temperatures (120, 130, and 140oC) and moisture contents (35, 40, and 45%). The expansion ratio decreased with increasing the moisture content. The hardness was negatively correlated with the expansion ratio. The bulk density decreased by increasing moisture content. The water holding capacity increased by increasing the moisture content and barrel temperature. Soaking time significantly (p<0.05) affected water stability and the best water stability was observed in all samples soaked for 1 h, but water stability was also stable at 2 h and 3 h. There was a significant increase in the protein digestibility of extruded fish feed, compared to that of the raw material.

Abstract
 Introduction
 Materials and Methods
  Materials
  Extrusion process
  Expansion ratio
  Bulk density
  Hardness
  Water stability
  Water holding capacity and swelling ratio
  Protein digestibility
  Statistical analysis
 Results and Discussion
  Expansion ratio
  Bulk density
  Hardness
  Water stability
  Water holding capacity and swelling ratio
  Protein digestibility
 Conclusion
 Acknowledgements
 References

• Xuelian Ma(Department of Food Science and Technology, Kongju National University)
• Bon-Yeob Gu(Department of Food Science and Technology, Kongju National University)
• Tie Jin(Department of Food Science and Engineering, Yanbian University)
• Jin-Hyung Yoo(Korea Aquatic Life Institute Co.Ltd)
• Mi-Hwan Kim(Department of Food Science and Technology, Kongju National University)
• Gi-Hyung Ryu(Department of Food Science and Technology, Kongju National University) Corresponding author