Effect of pH on functional characteristics of soy protein was investigated by modifying soy flour through acid (HCI) or alkali (NaOH) addition. Acid-and alkali-treated proteins were evaluated and texturized by twin-screw extrusion. Products were analyzed by rheological, functional, and ultrastructural methods. Acid-modified texturized protein had little expansion, increased peak force, increased work of shearing, and a nonoriented fiber arrangement. Slightly alkaline extrudates had increased rehydration but poorer texture. Stronger alkaline treatment resulted in denser products with high peak force measurements, which disintegrated when extrudates were rehydrated. The physicochemical state of soy protein, particularly conformation and protein-water interactions as affected by pH, may influence expansion of textured products and development of plexilamellar structure.
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