The aim of this study was to evaluate the optimization extrusion variables on quality of textured vegetable protein by using response surface methodology. In this study, 50% soy protein isolate, 40% wheat gluten, and 10% corn starch were blended and 15% of the mixture was substituted with green tea. The moisture content (45, 50, and 55%), barrel temperature (130, 140, and 150oC), and screw speed (100, 150, and 200 rpm) were varied. A Box- Behnken design was used in this experiment. Second order polynomial regression equations were developed to relate the response to extrusion variables as well as to obtain a response surface plot. The independent variables had significant effects on the quality of the products and moisture content was the most significant. The lower moisture content led to the higher integrity index, lower nitrogen solubility index, lower water absorption capacity, higher texture, and higher cutting strength. The optimum conditions were identified as moisture content 47.78%, barrel temperature 150.00oC, and screw speed 196.05 rpm. Incorporation of green tea into protein materials could effectively improve the nutritional value of the product. Understanding these optimized extrusion variables on the product quality was useful for producing textured vegetable protein in the future.

Introduction
 Materials and Method
  Materials
  Extrusion process
  Integrity index
  Nitrogen solubility index
  Water absorption capacity
  Texture profile analysis
  Cutting Strength
  Experimental design and statistical analysis
 Results and Discussion
  Integrity index
  Nitrogen solubility index
  Water absorption capacity
  Hardness
  Springiness
  Cohesiveness
  Chewiness
  Cutting strength
 Conclusion
 Acknowledgment
 References

• Xuelian Ma(Department of Food Science and Technology, Kongju National University)
• Bonyeob Gu(Department of Food Science and Technology, Kongju National University)
• Gihyung Ryu(Department of Food Science and Technology, Kongju National University) Corresponding author