SUPERMOLECULAR ASPECTS OF XANTHAN LOCUST BEAN GUM GELS BASED ON RHEOLOGY AND ELECTRON-MICROSCOPY

The viscoelastic properties and supermolecular structure of synergistic gels, formed by xanthan and locust bean gum (LEG) of two different mannose:galactose ratios (M:G), have been investigated by small deformation viscoelastic measurements and by low angle rotary-shadowing for transmission electron microscopy. The rheological properties at 20 degrees C for mixtures subjected to heating and cooling cycles in the temperature range 30-80 degrees C were found to be dependent on the M:G ratio. Mixtures of xanthan and LEG mixed at temperatures 140 degrees C were found to form true gels with low phase angles. Blends of xanthan and LEG with a low M:G ratio did not show any increase in synergistic effects as the temperature was increased, whilst the mixture of xanthan and LEG with a high M:G ratio showed a strong increase in synergistic effects as the temperature was raised above 60 degrees C. A difference in gelation temperature (T-g) of similar to 13 degrees C was observed between the mixtures of xanthan and the two LEG fractions. The T-g for xanthan with a high M:G ratio was similar to 53 degrees C, whilst the T-g for mixtures of xanthan and LEG with a low M:G ratio was similar to 40 degrees C. Results obtained using electron microscopy showed that the xanthan-LBG network was formed from xanthan supermolecular strands, and addition of LEG did not influence the xanthan structure. The observed structural features of the gels were independent of heat treatment and LEG fraction. The structural similarities and theological differences observed between xanthan and the LEG fractions are discussed in comparison with existing interaction models at the molecular level. Based on these results, a speculative network model at the supermolecular level is presented.