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

The viscoelastic properties and supermolecular structure of synergisti c gels, formed by xanthan and locust bean gum (LEG) of two different m annose:galactose ratios (M:G), have been investigated by small deforma tion viscoelastic measurements and by low angle rotary-shadowing for t ransmission electron microscopy.The rheological properties at 20 degre es C for mixtures subjected to heating and cooling cycles in the tempe rature range 30-80 degrees C were found to be dependent on the M:G rat io. Mixtures of xanthan and LEG mixed at temperatures 140 degrees C we re found to form true gels with low phase angles. Blends of xanthan an d LEG with a low M:G ratio did not show any increase in synergistic ef fects 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 fo r xanthan with a high M:G ratio was similar to 53 degrees C, whilst th e 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 th at the xanthan-LBG network was formed from xanthan supermolecular stra nds, and addition of LEG did not influence the xanthan structure. The observed structural features of the gels were independent of heat trea tment and LEG fraction. The structural similarities and theological di fferences 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 supermole cular level is presented.