EFFECT OF THERMAL-DENATURATION ON THE TEXTURIZATION OF SOYBEAN PROTEIN VIA TWIN-SCREW EXTRUSION

The texturization performance of thermally modified soybean flours, with nitrogen solubility indices (NSI) ranging from 80.0-8.6%, was evaluated using a twin-screw extruder under steady-state conditions. Following extrusion, the rheological, functional and ultrastructural properties of the textured products were examined. Heat processing resulting in NSI values between 35.4 and 23.7% was shown to decrease expansion and water absorption capacity and increase shear peak force of the finished product. Extrudates obtained from excessively thermally processed flours (8.6% NSI) exhibited limited texture development and disintegrated upon rehydration. Mild heat denaturation (> 57% NSI), however, resulted in products with excellent rheological and functional characteristics. Analysis of the feed properties such as water holding capacity and viscosity of the heat denatured flours indicated trends that could be correlated with product characteristics, thus providing additional information on the mechanisms governing texturization. Scanning electron microscopic examinations of dried extrudates revealed microstructural features which corresponded with extrudate properties.