Rheological Properties and Particle Size Distribution of Soy Protein Isolate as Affected by Drying Methods

Abstract

Soy protein isolate (SPI) solution prepared by ultrafiltration was dried using spray, freeze and oven dryers. Rheological properties (storage and loss modulus, complex viscosity, loss tangent), protein solubility and particle size distribution (D4,3, D3,2 and span) of different isolate powders were compared with commercially available counterpart. Commercial SPI showed a shear thinning behavior while rest of the samples exhibited a shear thickening behavior. Commercial and oven dried SPI (60 °C for 48 hours) SPI shown almost constant loss tangent less than unity during oscillation test which indicated its solid or gel property. Commercial and oven dried SPI samples had comparable size distribution whereas freeze dried SPI shown higher peak and narrow distribution pattern. Commercial SPI had lesser uniformity compared to rest of the samples. Water solubility index of spray dried SPI samples were high compared to freeze and oven dried samples.