Chemical and Functional Properties of Food Saccharides

© 2004 by CRC Press LLC
marketed on the basis of molecular size classes and can provide some differences
in rheology.
Although LBG does not itself form gels, it can be used together with other
hydrocolloids to provide gel formation. This synergistic gel formation can be
observed with other nongelling polysaccharides such as xanthan gum as well as with
the gelling algal polysaccharides, that is, the agars, carrageenans, 32 and furcelleran.
This property was attributed to the ability of nonsubstituted regions of the linear
mannan backbone to form hydrogen bonds with helical regions of other hydrocolloids
and provide cross-linking. 33,34 More recent observations have indicated that in
the interaction with xanthan gum, both polysaccharides adopt a helical conformation
and the junction between xanthan and LBG may be formed by a mixed double helix
in which chains from both polysaccharides participate. 35,36 Synergistic gel formation
can also be observed with other galactomannans, depending on the frequency of
galactose substitution on the mannan chain.
LBG is widely used as a thickener and stabilizer in many foods such as ice
cream, cheese spreads, salad creams, processed meats products, and pie fillings. It
can also be used to prepare a chocolate substitute, carob chocolate. A major use of
LBG and guar is in ice cream, where they can act as stabilizers to prevent ice crystal
growth at low temperatures. The presence of large crystals imparts a rough texture
to ice cream, reducing its palatability.
15.4.1.2 Guar Gum
Guar gum has long been used as a food ingredient in India but was developed
commercially in the aftermath of World War II, which interrupted traditional supplies
of LBG. Subsequently, guar has been cultivated in the southern U.S., which is now
a major source of the gum.
Guar is a linear β(1-4) mannan with a higher proportion of galactose substituents
than LBG has, having a galactose-to-mannose ratio of 1:2, and this is reflected in
the easier dispersion of guar gum when compared with that of LBG. Guar gum can
be dissolved at lower temperatures (typically at 20°C) as the extent of unsubstituted
regions of the mannan chain is lower, limiting opportunities for interchain hydrogen
bonding that would form aggregates and prevent hydration.
The rheology of guar gum is similar to that of LBG, pseudoplastic and decreasing
with temperature, with good pH stability. 37 Gel formation is observed only when
other polysaccharides are added, but the ability of guar gum to participate in synergistic
actions is lower than that of LBG. Again, this can be attributed to the reduced
extent of galactose-free regions of the mannan backbone that would be available for
close hydrogen bonding with another polysaccharide. The uses of guar gum are
similar to those listed for LBG, reflecting its original commercial introduction as a
substitute for LBG.
15.4.1.3 Tara Gum
Tara gum has a galactose-to-mannose ratio of 1:3, intermediate between those of
LBG and guar gum. Rheological properties are similar to those of LBG. 38 Although