Stress relaxation in synergistically associated polysaccharides: Galactomananns and a non-pectic polysaccharide fraction from yellow mustard mucilage

In the current study, stress relaxation test and dynamic temperature sweep test were performed to study a non-pectic polysaccharide (NPP) fraction from yellow mustard mucilage and its synergistic interactions with galactomannans (GMs). All solutions were prepared at the total polysaccharide concentration of 1% (w/v). NPP and GM were mixed at the blending ratio of 7/3. Prior to measuring the behaviour of the mixed solutions, the effects of temperature and pH on 1% NPP solution were studied. The results showed that both acidic condition and increased temperature led to stronger NPP gels due to hydrophobic interactions along the NPP backbones. When NPP was mixed with either fenugreek gum (FG) or locust bean gum (LBG) at pH 8, synergistic interactions were observed at all examined temperatures. The relaxation modulus (G(t)) increased at higher temperatures. The difference in relaxation curves between the two mixed solutions, NPP/FG and NPP/LBG, at increased temperatures further confirmed the difference in their synergy mechanism: the breakdown of “hyperentanglements” in NPP/FG solution started at a lower temperature (50 °C) while the breakdown of “junction zones” via hydrogen bonding in NPP/LBG solution occurred at a higher temperature (70 °C). This paper provides further evidence for our previously proposed mechanisms of the synergistic interactions in NPP/FG and NPP/LBG mixed systems.