Modification of soy-wheat protein functionality by co-precipitation and its extrusion performances

This investigation will compare the functional characteristics of native, co-precipitated and blended proteins. Experiments will be designed to better understand the mechanisms involved in the texture formation of the co-precipitated protein, and determine the most suitable conditions and compositions for co-precipitation leading to better textured products.Co-precipitated proteins were prepared from soy flour and wheat gluten, by either direct acid-precipitation at different pH or alkaline-treatment followed by acid precipitation; the effects of processing methods on their functional properties were established. A flavorless co-precipitated product with excellent functional characteristics was obtained. Viscosity, gelation and foaming stability characteristics were superior in comparison with those of the native proteins. Alkaline pretreatment at pH 9.5, which facilitated proteins unfolding, improved the functionality of co-precipitated protein. Protein solubility results suggested that hydrophobic bonding plays an important role in protein-protein interaction during protein co-precipitation, while maximum interaction was found when proteins were co-precipitated at pH 4.5.The texturization performance of co-precipitated proteins extruded using a Werner & Pfleiderer ZSK-30 twin-screw extruder was investigated. The effects of co-precipitation pretreatment and the influence of shear and moisture content on the characteristics of texturized proteins were studied using response surface methodology. The key reaction mechanisms taking place during the texturization of plant proteins were elucidated. The results showed that texturized protein characteristics can be controlled by varying screw speed and moisture content in the feeding materials. Textural properties such as chewiness, hardness and cohesiveness increased with decreasing screw speed from 450 rpm to 350 rpm and increasing moisture content in the feeding materials from 25% to 35%. Co-precipitated proteins from soy flour and wheat gluten at 1:1 ratio and pretreated at pH 8.5 resulted in the best textural characteristics. Co-precipitation appears to be an excellent approach to improve the textural properties of extruded soy proteins.U of I OnlyETDs are only available to UIUC Users without author permissio