ガティガム

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説明

Gum ghatti is an exudate from the tree Anogeissus latifolia, family Combretaceae, a large tree widely distributed in India and Ceylon. It is a complex, water-soluble polysaccharide composed of the calcium and magnesium salts of L-arabinose, D-galactose, D-mannose, D-xylose, D-glucuronic acids in the approximate molar ratio of 10:6:2:1:2. It is light to dark tan and is insoluble in 90% alcohol.
The tree Anogeissus latifolia, from which gum ghatti is exuded, is also used as a source of timber, and its tannin-rich leaves are used for tanning. It grows extensively in India and Ceylon. Production, collection, and processing methods are very similar to that for gum karaya. The gum is exuded when the bark is damaged, probably to act as a sealant. It is gathered by hand in the dry season by natives whose usual occupation is farming. The largest crop is normally picked in April. After drying for several days, the gum is transported to Bombay, usually having to be transported through mountain passes, or ghats, hence the name gum ghatti. In Bombay, the crude gum is sold by auction to exporters, who first have it classified by hand according to color and purity. In the United States, the process grinds the tears to a fine particle size. Impurities are reduced by sifting and aeration.
Gum ghatti is essentially a calcium salt of ghattic acid, a polysaccharide with a molecular weight of approximately 12,000. Hydrolysis products are L-arabinose (5 moles), D-galactose (3 moles), D-mannose (1 mole), D-xylose (0.5 mole), D-glycuronic acid (1 mole), and traces of 6-deoxyhexose. Two aldobiouronic acids, 6-0-(P-D-glucopyranosyluronic acid)-D-galactose and 2-0-(|5-dglucopyranosyluronic acid)-D-mannose are obtained on graded hydrolysis. The gum contains chains of 1,6-lined ji-D-galactopyranose residues, to which the aldobiouronic acid units are attached, either directly or through one or more 1,6-linked glactose residues.
Gum ghatti can be dispersed in water to form a colloidal dispersion. Only about 80-90% of the gum is actually soluble. It is quite stable over the pH range 3.5-10.0. It is a natural buffer and small amounts of acid or alkali will not affect viscosity.
Its properties are usually considered to be similar to gum arabic, but its solutions are more viscous and less adhesive. Use of gum ghatti in foods is based primarily on its effectiveness as an emulsifier for oil and water emulsions. However, solutions of ghatti are more viscous and less adhesive than those of arabic.