Investigation into the physiochemical properties of soy protein isolate and concentrate powders from different manufacturers

The physiochemical properties of five commercially available soy protein isolates (SPI) from different manufacturers and one soy protein concentrate were analysed. Despite their identical botanical origin and an almost interchangeable molecular weight profile, remarkable differences were revealed in their solubility, protein dispersibility index (PDI), water holding capacity (WHC), zeta potential (measured at different pHs) and particle size distribution. Protein solubility and PDI values, which can be considered as a simple and reliable measure of soy protein powder's suitability for industrial formulations such as extrusion premixes, revealed to be strongly intercorrelated, with SPI A, B and E showing higher values at pH 7.0 and 9.0 as compared to their counterparts (sample C and D). WHC appeared to be less influenced by solubility, but greatly by particle size distribution. SPI A, B and E showed largest increase in diameter upon hydration ('swelling') and gave the highest WHC. Varied physiochemical properties observed in soy protein powders showcased correlated trends between solubility, particle size and water-holding capacity (WHC). This study highlights the importance of narrow particle size distribution and high solubility/PDI, emphasising their impact on product quality and advocating for rheological assessments in thermal processing.image