2.1.4 Inulin
It is found to bear a close resemblance to starch except that it is a levulan rather than a dextran. The following characteristic features make it altogether different from starch, namely:
* Gives yellow colouration by iodine.
* Does not gelatinize with water.
* Not commonly found in plants in the form of granules having concentric layers, and
* Upon hydrolysis in acidic medium yields fructoses.
Synonyms Dahlin; Alantin; Alant starch.
Biological Source It occurs in certain plants of the Compositae family, such as:
Inula helenium Linn. : Roots contain inulin;
Eupatorium cannabinum Linn. : Plant contains inulin;
Cynara scolymus Linn. : Flower heads contain inulin;
Carpesium cernuum Linn. : Roots contain inulin;
Calendula officinalis Linn. : Roots contain inulin;
Aretium lappa Linn. : Roots contain 45% inulin.
Geographical Source
A. lappa – Western Himalayas from Kashmir to Simla;
C. officinalis – India, Pakistan;
C. cernuum – Temperate Himalayas and Nilgiri Hills (India);
S. scolymus – Throughout India; E. canabinum—Temperate Himalayas;
I. helenium – Europe and Asia.
Preparation Isolated from dahlia tubers and from other members of the family Compositae.
Description The crystals are spherical in shape when prepared from water.
Chemical Constituents
[Structure of INULIN showing arrangement of Fructofuranose residues in chain]
Inulin is quickly hydrolyzed by acids to D-fructose by the enzymes inulase but does not undergo hydrolysis by the amylases. However, methylated inulin upon hydrolysis gives rise to 3,4,6-trimethylfructose as a major product and 1,3,4,6- tertamethylfructose as a minor product, thereby suggesting that the fructose residues are present in the furanose form and the adjacent units are joined through C-1 and C-2 (i.e., the glycosidic hydroxyl moiety).
Uses
1. It is used in culture media as a fermentative identifying agent for certain bacterial species.
2. It is filtered exclusively by the glomeruli and is neither secreted nor reabsorbed by the tubules. Hence, it is employed as a diagnostic agent for evaluation of glomerular filteration i.e., renal–function test (or kidney function test).
3. It is considered to be valuable in the diet of the diabetic patients.
