The objective of this study was to determine chemical compositions affecting the physical and thermal properties of the textured vegetable protein (TVP). The 14 commercial TVPs were pulverized, followed by analyzing their morphology, chemical composition, water absorption index (WAI) and water solubility index (WSI) (for the pulverized and original TVPs), solubility, swelling power, melting property, and hardness. All TVPs showed the rough surface with irregular cracks and pores and the porous structure with varied pore sizes. WAI was positively correlated to moisture and crude protein contents and negatively correlated to the total carbohydrate content. WSI and solubility were directly and reversely influenced by the crude ash and total carbohydrate contents and the crude protein and total starch contents, respectively. The swelling power and melting temperature of TVPs did not significantly affect chemical compositions. Melting enthalpies increased with crude ash content, while decreased with the total starch content. The hardness of the rehydrated TVPs was enhanced with their crude ash and total carbohydrate contents, whereas reduced with their crude protein and total starch contents. Overall, the yield and texture of the rehydrated TVP could be modulated with the crude protein and ash contents of TVP.

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.