Hydrodynamic behavior and gelling properties of sunflower head pectin in the presence of sodium salts

Abstract

Hydrodynamic behavior and gelling properties of sunflower head pectin (SFHP) regulated by sodium salts were investigated. Huggins plots of SFHP solutions at different pH in the presence of NaCl and Na2SO4 (0.01, 0.05 and 0.10 M) were depicted by capillary viscometric analysis. The gelling process of SFHP solution (1%, w/v) during cooling from 75 °C to 10 °C induced by NaCl and Na2SO4, respectively, was monitored by rheological tests. The gel strength and gel stability were also examined. Experimental results indicated that the variation of hydrodynamic behavior of SFHP was the combined result affected by both pH and sodium salts. Under the inducing of sodium salts, the SFHP gel was developed according to a two-phase mechanism. NaCl presented higher inducing efficiency, resulting in rapid but inhomogeneous aggregation of SFHP and the formation of opaque and brittle gel. Oppositely, Na2SO4 induced a relatively slow and homogeneous gelation, leading to the formation of transparent and hard gel. Gel structure induced by sodium salts was maintained by molecular interactions, especially hydrogen bonds. Addition of 20% (w/w) sucrose can reduce strength of all gels by about 25%. Sucrose also increased stability of CaCl2-gel and NaCl-gel but showed no influence on Na2SO4-gel.