Carob and Locust bean gum – LBG properties

LBG properties

LBG comes in a variety of forms, basically they can be divided into high grade, industrial and technical (Wielinga, 1989). A basic composition of the different grades can be seen in the table below. For those buying LBG the key parameters to be aware of are:

1. Acid insoluble residues gives an indication of how well the skin has been removed from the seed. Hence the lower the acid insolubles the better.
2. Protein gives an idea of how well the germ has been separated from the endosperm. Hence the lower the protein level the better.

Carob pod split open

The polysaccharide from the endosperm is a long chain β-(1-4)-mannose polymer with α-(1-6)-galactose units appearing as single unit side chains. This puts the galactomannan in the same general family as other polysaccharides such as guar, fenugreek, tara and cassia. The ratio of galactose to mannose in LBG is roughly 1:4. The distribution is believed to be roughly random although this area has not been adequately investigated in terms of relating structure to variety. Recent work by Henk Schols at Wageninen in the Netherlands (11th Wrexham conference) has shown that there are considerable variations across a selection of LBG sources. However the work was flawed by not identifying the source of each LBG sample in terms of variety, region and farming/harvesting conditions, but the main point, that there are differences, was proved. However the techniques exist to elucidate the structure of a galactomannan (Mc Cleary) and it would be extremely useful to identify structural variations between varieties or farming/harvesting conditions and relate this to functional properties such as synergism with other gums and performance in end use applications.

LBG is only partially soluble in cold water. The mannan sections of the polymer chain can bind together to form a crystalline region which is thermodynamically more stable than the solution state. Hence even when in solution at ambient temperature there is a tendency for the polymer chains to wish to aggregate. This makes the accurate measurement of molecular weight difficult due to the presence of aggregated species in solution. However it also has some advantages. The aggregation can be increased by reductions in water activity and reduction in solution temperature which ultimately forms a 3D network and a gel. This is exactly what happens in ice cream during freezing. Their are two great advantages of this: firstly a weak gel structure does not impart a slimy or slippery mouth feel to the ice cream and more critically the formation of a weak gel on cooling imparts excellent meltdown resistance to the ice cream.

The synergy of LBG with kappa carrageenan is the basis of the majority of non gelatin dessert jellies as well as most of the jelly used in canned pet foods. The texture of a LBG/carrageenan gel can be manipulated to be close to gelatin and the higher melting temperature is a positive advantage in warmer countries or countries where refrigeration is not present in every household.

The synergy of LBG with kappa carrageenan is the basis of the majority of non gelatin dessert jellies as well as most of the jelly used in canned pet foods. The texture of a LBG/carrageenan gel can be manipulated to be close to gelatin and the higher melting temperature is a positive advantage in warmer countries or countries where refrigeration is not present in every household. It is also known that the melting point of the synergistic gel can be manipulated by altering the molecular weight of the LBG. This probably has more use in terms of aiding processing than it actually does in terms of providing a melt in the mouth sensation.

LBG has several functional properties that its users are looking for. One of the largest food uses of LBG is in cream cheese where it is used to bind water and produce a spreadable texture without imparting sliminess.

There have been several patents and articles covering different ways to manufacture or mimic LBG from a different source. The only method known to have been commercialised is the treatment of guar with an alpha-galactosidase enzyme to produce a galactose depleted guar with properties similar to LBG.