A comparison of the rheological behaviour of crude and refined locust bean gum preparations during thermal processing

The behaviour, during thermal processing, of a higher quality analytical-grade (AG) locust bean gum (LBG) was compared with a lower quality technical grade (TG) LBG. The TG material contained a substantial amount of material (40%) of dry weight, which remained insoluble after heating to 70°C. Sugar analysis suggests that this insoluble material contained high levels of arabinose. The TG material showed low viscosity throughout the heating cycle and lower levels of degradation at high temperatures, as evidenced from viscosity measurements. The reason for this could have been that, in these samples, the viscosity is dominated by the non-soluble particulates in the system; however, on removal of particulates further rheological studies, made at comparable galactomannan concentrations, also showed differences between the degradation of the AG and TG LBG. Despite the difference in behaviour through the heating cycle, at equal galactomannan levels, the AG and TG materials had similar viscosities at the end of this cycle. This may explain why, after heat processing, the TG material interacts synergistically with carrageenan in a similar way to AG locust bean gum.