The degree of protein aggregation in whey protein isolate-based dispersions modifies their surface and rheological properties

This work aims to study the effect of degree of protein aggregation on the surface and rheological properties of whey protein isolate dispersions with different concentrations (80, 100 and 120g/kg), pHs (5.5 or 6.5) or NaCl contents (1 or 2g/kg). Dispersions were thermally treated at 70, 75 and 80 degrees C for different times. By mixing aggregated with native protein dispersions, different degrees of aggregation (0%, 20%, 40%, 60% and 80%) were obtained. Surface tension of the dispersions was determined by the pendant drop method, whilst their rheological properties were obtained from flow curve tests. A slight effect of the degree of aggregation over diffusion was found, which indicates that native proteins dominated the decrease in surface tension. The rheological behavior of dispersions with NaCl addition changed from Newtonian to shear thinning for aggregation degrees above 20%, whilst all dispersions at pH 5.5 and 6.5 presented a shear thinning behavior. RESUMENEste trabajo apunta a estudiar el efecto del grado de agregacion de proteinas en las propiedades de superficie y reologicas de dispersiones de ASP con diferente concentracion de proteina (80, 100 y 120 g/kg), pH (5,5 o 6,5) o contenido de NaCl (1 o 2 g/kg). Las dispersiones fueron tratadas termicamente a 70, 75 y 80 degrees C por diferentes tiempos. Mediante la mezcla de dispersiones de proteina agregada y nativa, se obtuvieron dispersiones con grados de agregacion diferente. La tension superficial de las dispersiones se determino fue determinada por el metodo de la gota colgante, mientras que las propiedades reologicas se obtuvieron desde ensayos de curva de flujo. Se encontro un efecto menor del grado de agregacion sobre la difusion, lo cual indica que las proteinas nativas dominaron la disminucion de la tension superficial. La reologia de las dispersiones con adicion de NaCl cambio desde un comportamiento Newtoniano a uno pseudoplastico para grados de agregacion sobre el 20%; mientras que todas las dispersiones a pH 5,5 o 6,5 presentaron un comportamiento pseudoplastico.