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Selective debranching of guar galactomannan by structurally unrelated enzymes for improved functional properties

Shobha, M. S. (2009) Selective debranching of guar galactomannan by structurally unrelated enzymes for improved functional properties. PhD thesis, University of Mysore.

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Abstract

Carbohydrates are the major representatives of naturally abundant bio-resources and undoubtedly they are the renewable raw materials of high (bio) – technological value. In the form of available (starch) and unavailable (dietary fiber) carbohydrates, they contribute a major portion of our diet, thereby providing a ready source of energy reserve and offer other beneficial physiological effects too. Galactomannans are one such complex carbohydrates which find importance due to their beneficial properties in food and non-food applications. Galactomannans are reserve polysaccharides of plant origin (mostly Leguminosae) present in the endosperm portion of seeds. Constituting a group of commercially important hydrocolloids, Galactomannans, contain a 1,4-linked β-D-mannan backbone to which are attached D-galactopyranosyl residues α-1,6-linked as side chain branches. Fenugreek, guar gum, tara gum and locust bean gum are the classical galactomannan sources with varying galactose to mannose ratios of approximately 1:1, 1:2, 1:3, 1:4, respectively. Of these, guar galactomannan, the most sought-after hydrocolloid, exhibits high viscosity in aqueous solution, is non-ionic, and easily available in large quantities. It finds considerable use in various food and non-food industries like pharmaceutical, textile, printing, drilling, mining, explosives, etc. In the food industry guar galactomannan is extensively used as a stabilizer in a variety of applications including ice cream, baked foods, soups, etc. It is also used as a thickener, syneresis control agent and as a formulation aid. The functional properties of guar galactomannan in controlling the release of drugs in the gastrointestinal tract for colon targeted drugs, anticancer drugs in the treatment of colorectal cancer, oral rehydration solutions in the Synopsis treatment of cholera and also as a visco-supplementation agent in osteoarthritis treatment are of pharmaceutical importance. As a source of water soluble fiber guar galactomannan serves as a fermentable substrate for the microflora normally present in GI tract. In addition, its other physiological properties are as hypocholesterolemic, hypolipidemic and hypoglycemic agent. Although it has numerous applications, additional uses of guar galactomannan are limited due to its high branching, high viscosity and high molecular weight. Though expensive, locust bean gum (LBG) continues to enjoy a better and specific usage because of its less branching (with galactose), which facilitates synergistic interaction with xanthan and other hydrocolloid gums forming thermo-reversible gels of use in specific food products. Nevertheless, innumerable attempts have been made in several labs all over the world with little success to convert guar galactomannan to LBG-type, by debranching using specific enzymes (α-galactosidase) from various sources like germinating guar seeds, coffee bean, etc., which resulted in the removal of a few galactose residues. As the production of α-galactosidase in pure form involves laborious steps, which is non-economical, a search for alternative sources of enzymes which are easily available and inexpensive was made. Our earlier studies have shown that several common enzymes such as pectinase, pepsin, papain, pronase, lysozyme, hemicellulase and lipase are involved (non-specifically) in the depolmerization of completely unrelated substrates, viz. chitosan. Sequel to this, a few of these enzymes were screened for any catalytic/debranching activities towards guar galactomannan. Infact, preliminary data indicated very encouraging results that prompted us to go further for detailed investigations. The main objective of the present study was to produce Synopsis modified guar galactomannan by selective enzymatic debranching, which mimics LBG in several of its rheological properties. Another objective of this study was to elucidate the mechanism for such non-specificity of pepsin in the removal of side chain galactose residues of guar galactomannan. Accordingly, the following work plan was envisaged to fulfill these two objectives. a. Screening of enzymes such as pectinase, pullulanase, pepsin, pronase, lipase and cellulase for depolymerization and debranching activities on guar galactomannan. b. To study the Gal-Man ratio, monomer sequence, viscosity and gelling characteristics of the modified guar galactomannan. c. To study kinetic parameters and to elucidate the mechanism of action by pepsin in its catalytic activity towards guar galactomannan, and d. To compare and contrast the rheological behaviour of modified guar galactomannan with those of LBG.

Item Type: Thesis (PhD)
Uncontrolled Keywords: Enzymes; Production of galactose; Guar galactomannan (GDGG); Rheology of GDGG
Subjects: 600 Technology > 08 Food technology > 16 Nutritive value > 01 Carbohydrates
500 Natural Sciences and Mathematics > 04 Chemistry and Allied Sciences > 28 Polysaccharide Chemistry
Divisions: Dept. of Biochemistry
Depositing User: Food Sci. & Technol. Information Services
Date Deposited: 18 Mar 2010 06:56
Last Modified: 18 Mar 2010 06:56
URI: http://ir.cftri.com/id/eprint/9399

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