Agriculture Reference
In-Depth Information
Fig. 8.1
Structure of (a) guar gum and (b) locust bean gum. M = mannose, G = galactose.
substituted or 'hairy' regions. This leaves lengths of mannose chains containing
no side groups, known as unsubstituted or 'smooth' regions.
The key property of LBG of interest to the food industry is its high viscosity at
low concentrations, making it an effi cient thickener. LGB is only partially soluble
in cold water, requiring solutions to be heated to at least 80°C for full hydration.
Also, solutions are very slightly cloudy due to the presence of small amounts of
protein and fi bre. For most applications this is not an issue, but higher priced LBG
can be obtained that has been alcohol-refi ned to remove these residues and which
gives clear solutions. Cold swelling versions of LBG are also commercially
available. LBG solutions show good stability to most food processing operations
and recipes, having good thermal and pH stability (except in highly acidic
conditions).
LBG does not gel on its own, but does form gels with other hydrocolloids.
Addition of LBG to gelling hydrocolloids, such as kappa carrageenan or agar,
increases the gel strength, and makes the typically brittle gels more elastic. Best
known is its synergistic interaction with xanthan. Neither xanthan nor LBG gel on
their own but mixing these two hydrocolloids produces a thermoreversible, elastic
gel. The xanthan/LBG gels also have the benefi t of being insensitive to common
cations (unlike gels of pectin, alginate or carrageenan). At very low concentrations
of xanthan and LBG, a weak gel network is formed. This gel is strong enough to
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