Whey protein isolate and flaxseed (Linum usitatissimum L.) gum electrostatic coacervates: Turbidity and rheology

Abstract

Listen

Translate article

Coacervates were prepared with flaxseed (Linum usitatissimum L.) gum (FG) and whey protein isolate (WPI) solutions in water. Structural transitions during coacervate formation were monitored by turbidimetry and zeta potentiometry. Biopolymer mixing ratio R (1:4–15:1, w/w) and pH (6.0–1.4) effects on pH-dependent phase transitions (pHc, pHϕ1, and pHϕ2) were examined. Where R = 1:1 (w/w), pHc, pHϕ1, and pHϕ2 were observed at pH 5.4, pH 5.0, and pH 1.8, respectively. The highest optical density (OD600 = 0.617 ± 0.009) occurred at pH 3.4, the pHmax. As R increased from 1:4 to 15:1, pHϕ1 and pHϕ2 also increased (pHϕ1 4.2 to 5.2 and pHϕ2 1.8 to 2.2). Accordingly, pHmax shifted from 3.0 to 4.8 while pHc was independent of R. The shift of pHmax was consistent with isoelectric point (IEP) of the WPI-FG mixture determined by electrophoretic mobility measurements. The maximum WPI-FG coacervate formation occurred at R = 2:1 (w/w) and pHmax = 3.8 with OD600 = 0.783 ± 0.018. Dynamic shear viscosity and viscoelasticity of WPI-FG coacervates were determined at a range of pH and R. WPI-FG coacervates exhibited shear-thinning behavior and gel-like properties. The highest dynamic viscosity and viscoelasticity of WPI-FG coacervates were observed at pH 3.8 with R = 2:1 (w/w). Electroneutrality of WPI-FG mixture favored coacervate formation with a more compact structure and improved rheological properties. Light microscopy observations revealed that uncharged WPI-FG mixtures formed coacervates that were more compact than charged coacervates and exhibited improved rheological properties.