2009_Book_FoodChemistry

312 4 Carbohydrates
4.4.4.10.2 Structure, Properties
The main locust bean polysaccharide is similar
to that of guaran gum: a linear chain of 1 → 4
linked β-D-mannopyranosyl units, with α-D-galactopyranosyl
residues 1 → 6 joined as side
chains. The ratio mannose/galactose is 3 to 6; this
indicates that, instead of every second mannose
residue, as in guaran gum, only every 4th to 5th
is substituted at the C-6 position with a galactose
molecule.
The molecular weight of the galactomannan is
close to 310 kdal. Physical properties correspond
to those of guar gum, except the viscosity of the
solution is not as high (cf. Table 4.21).
Fig. 4.23. Viscosity of 1% aqueous guar solution at
25 ◦ C versus shear rate (rpm.). Viscometer: Haake rotovisco
(according to Whistler, 1973)
4.4.4.9.3 Utilization
Guaran gum is used as a thickening agent and
a stabilizer in salad dressings and ice creams (application
level 0.3%). In addition to the food industry,
it is widely used in paper, cosmetic and
pharmaceutical industries.
4.4.4.10 Locust Bean Gum
4.4.4.10.1 Occurrence, Isolation
The locust bean (carob bean; St. John’s bread)
is from an evergreen cultivated in the Mediterranean
area since ancient times. Its long, edible,
fleshy seed pod is also used as fodder. The dried
seeds were called “carat” by Arabs and served as
a unit of weight (approx. 200 mg ). Even today,
the carat is used as a unit of weight for precious
stones, diamonds and pearls, and as a measure of
gold purity (1 carat = 1/24 part of pure gold).
The locust bean seeds consist of 30–33% hull
material, 23–25% germ and 42–46% endosperm.
The seeds are milled and the endosperm is separated
and utilized like the guar flour described
above. The commercial flour contains 88% galactomannoglycan,
5% other polysaccharides, 6%
protein and 1% ash.
4.4.4.10.3 Utilization
Locust bean flour is used as a thickener, binder
and stabilizer in meat canning, salad dressings,
sausages, soft cheeses and ice creams. It also improves
the water binding capacity of dough, especially
when flour of low gluten content is used.
4.4.4.11 Tamarind Flour
4.4.4.11.1 Occurrence, Isolation
Tamarind is one of the most important and widely
grown trees of India (Tamarindus indica; dateof
India). Its brown pods contain seeds which are
rich in a polysaccharide that is readily extracted
with hot water and, after drying, recovered in
a powdered form.
4.4.4.11.2 Structure, Properties
The polysaccharide consists of D-galactose (1),
D-xylose (2) and D-glucose (3), with respective
molar ratios given in brackets. L-Arabinose is
also present. The suggested structure is presented
in Formula 4.145.
The polysaccharide forms a stable gel over
a wide pH range. Less sugar is needed to achieve
a desired gel strength than in corresponding
pectin gels (Fig. 4.24). The gels exhibit only
a low syneresis phenomenon.