Xyloglucan is a component of the cell walls of higher plants. There have recently been some exciting suggestions regarding the biological roles of xyloglucan. Xyloglucan cross-links plant cellulose microfibrils and provides flexibility. Xyloglucan metabolism controls the elongation of plant cell. Furthermore, xyloglucan from seeds of the tamarind tree (Tamarindus indica) has been used as a thickener and gelling agent in food processing. Of greater interest is the fact that xyloglucan can confer novel rheological properties to the aqueous phase.
Xyloglucan has a β-1,4-glucan backbone with 1,6-α-xylose side chains. Some of the xylose residues are β-D-galactosylated at O-2. The architecture of xyloglucan has been investigated by light scattering and small-angle X-ray scattering. A new method of conformation analysis has been proposed, i.e., Monte Carlo simulation based on molecular mechanics combined with small-angle X-ray scattering. The stiffness of the chains or “hyperentanglements” has been discussed. In solution, xyloglucan exhibits typical Newtonian flow and is very stable against heat, pH and shear. It provides an elastic gel with a concentrated sugar. Tamarind seed xyloglucan has many applications, and is used as a sauce thickener and in ice cream, dressing and processed vegetables. It is often called “aging-free starch”, since it has properties similar to those of starch but is more stable.
Various physiological and biological activities of xyloglucan have been reported. Xyloglucan hydrolysates exhibit plant growth-promoting activity that resembles that of auxin. Recently, the suppression and acceleration of cell elongation by the integration of xyloglucans have been reported. Various physiological effects of dietary fiber, such as its ability to control blood glucose and reduce lipids, have received considerable attention. These effects are important in the treatment and prevention of geriatric diseases. Xyloglucan and hydrolyzed xyloglucan have been shown to improve lipid metabolism and reduce the weight of adipose tissue. Other physiological functions include the concept of carbohydrate-regulation in response to environmental stimuli in animals.
The enzymatic modification of xyloglucan to elicit new biological functions or unique properties is highlighted. Xyloglucan from which galactose has been partially removed by âgalactosidase has a unique property of heat-induced reversible gelation, and reverts to sol upon cooling. This gelation is caused by the formation of a cross-linked domain by a flat structure with rod-like chains. A good understanding of the structure-function relationship has been developed.
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