Effect of kappa-carrageenan on phase separation of milk proteins and polysaccharide stabilizer in sucrose solution simulating ice cream mix system
Milk proteins and polysaccharide stabilizers commonly exhibit phase separation when they are mixed. Practical experience has shown that [kappa]-carrageenan can prevent phase separation. However, not much research has been conducted on the quaternary system of [kappa]-carrageenan/primary stabilizer/milk protein/sucrose solution, especially rheological properties. The effects of heat treatment, homogenization, and butteroil, added to simulate ice cream mix, on rheological properties were studied using a dynamic controlled stress rheometer. Phase diagrams and transmission electron microscopy (TEM) were used to investigate structural formation at the macroscopic and microscopic levels, respectively. Gel electrophoresis was used to analyze milk protein surface concentration in systems with butteroil. Disappearance of phase separation between milk proteins and primary stabilizers in sucrose solution at the macroscopic level was evident with added [kappa]-carrageenan but the existence of phase separation at the microscopic level was still present. Phase separation was attributed to a depletion flocculation mechanism while disappearance of this phenomenon was attributed either to a weak filament gel-network of [kappa]-carrageenan, adsorbed on caseins via electrostatic interaction, or to a gelation of excess [kappa]-carrageenan itself. Pseudoplastic behaviour and elastic-like characteristics were more evident with increasing concentration of [kappa]-carrageenan in all quaternary systems with different types of primary stabilizers. Heat treatment effectively increased thixotropic characteristics of these quaternary systems. Homogenization possibly reduced chain length of LBG, xanthan, and [kappa]-carrageenan, leading to less self-association of xanthan but more synergistic effect between LBG and [kappa]-carrageenan. This resulted in less elastic-like behaviour in the former and less viscous behaviour in the latter, as demonstrated by a higher tan [delta] and a lower tan [delta], respectively. Such structural characteristics were shown by TEM. When adding butteroil, thixotropic characteristics were more evident in systems comprised of xanthan than LBG systems. However, the more [kappa]-carrageenan added into systems with butteroil, the more solid-like characteristic. The results from SDS-PAGE showed that LBG or xanthan with or without [kappa]-carrageenan significantly affected milk protein concentration on the butteroil droplet surface.