Page 7 - Physicochemical properties of Indian plant gums- IINRG, Ranchi

Babul gum (Acacia nilotica)

General Information

Babul (1. nilotica subsp. lndica\. a moderate_sized, alrnost evergreen tre. is found
ttroughout the drier parts of India. Bark of the tree is dark brown to almost black,
longitudinally flssured or deeply cracked- The gum exudes from wounds in the bark,
mostly dwing March-May. The gum obtaind from Acacia n,otica is.known as ..rndian
gum arabic". Though some trees yield a maximum of around lkg per year, the average is
only a few grams. The yield lessens with rhe age of the trees. ti is uelre,rea that tapiing
accelerates the flow, but it is not often practiced- Incisions made (6cm x lcm ana td"m i
0.5cm) have shown maximum yield l2gltree./annum-
Thg
eum of A. nilotica stbsp. Indica, arthough called gum arabic, is not true gum arabic
which is obtained from A. senegal.

Physico-chemical properties

Babul gum occurs in the form of rounded or ovoid tears about 1cm in size and the colour
varies from pale-yenow to brown or almost brack according to the age of the tree and the
conditions of collection.

The gum is tasteless and almost completely soluble in water (50g/l00ml). The darker
samples contain tarmin and are much less soluble, and leave behind a gelatinous residue.

Babul gum is very slightly dextrorotatory whereas the gum of A. senegal is slightly
laevorotatory

It contains 13% of moisture and on ignition, it leaves behind 1.g% ofash (CaO
,52.2; and
MgO, 19.7o/o).
Motecular weighl.. The gum ofl. nilotica has ahigher molecular weight (Mw, 2.3 x 106)
than A. Senegal (Mw, 600,000).

Clenical natute : The gum contains galactose, L-arabinose, L_rhamnose, and four
aldobiouronic acids, viz. 6-0-(
B-glucopyranosyluronic acid)_D-galactose; 6_0_(4_0_
mehtyl-ftDglucopyranosyluronic acid)-D_galactose; 4_O-(c_D-glucopyranosyluronic
acid)-D-galactose and 4-O-(4-O-met\l-o-D-glucopyranosyluronic
acid)_D_galactose.
The 3, 5, di4-methyl-L-arabinose and a new crystalline arabinobiose, 2_O_p
-L-arabinopyranosyl-L-arabinose (C,oH,*Oo. % I!O, mp l03C) have been isolated from the
gum. It also contains arabinobiose, 3-o-ftL-arabLopyranosyl-L-arabinose.
The structural
evidence suggests that gum molecules possess highry branched galactan ffameworks to
which are attached uronic acid residues and arabinose-containing side chains.