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Esterases from finger millet malt and their effect on the functionality of cereal non-starch polysaccharides.

Madhavi Latha, G. (2007) Esterases from finger millet malt and their effect on the functionality of cereal non-starch polysaccharides. PhD thesis, University of Mysore.

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Cereal plant cell walls are complex mixture of polysaccharides consisting of arabinoxylans, (1→3)/(1→4)-β-D-glucans, arabino-galactoproteins and glucomannans, in addition to the high amounts of lignocellulosic complexes. Considerable progress was made for the past few decades on the functional aspects of cereal arabinoxylans due to their potential influence on water holding capacity and water balance, protein foam stabilization, viscosity, gelling and rheological properties. Cereal arabinoxylans are β-1, 3/1, 4 linked D-xylose polymers with a large variation on the nature and position of the substituents in the side chain. Minor substituents such as acetyl (attached at O-2/O-3 of the xylan backbone), as well as feruloyl groups (esterified to 5'-OH group of arabinosyl residues in the side chain), are also present in the side chains of arabinoxylans. The structure of these arabinoxylans varies not only from source to source, but also with in the same source. Arabinoxylans have been characterized from various sources such as wheat, barley, maize, rye and ragi with respect to their structural and functional relationship. Nutritionally, arabinoxylans are known to alleviate various disease symptoms such as diabetes, atherosclerosis and colon cancer. Malting of cereals/millets is an important biotechnological process which helps in the induction of various hydrolytic enzymes such as α/β-amylases, α-glucosidases, pullulanases, xylanases and esterases, which in turn, controls the various physiological and biochemical processes in the grain. The information pertaining to both starch and major cell wall degrading enzymes such as xylanases and xylosidases from cereal malts is quite exhaustive. However, the same is not true with respect to the minor cell wall degrading enzymes such as O-acetyl esterases and feruloyl esterases. ii Esterases are important class of hydrolytic enzymes that cleave the ester linkages i.e. acetic acid esterases (EC cleaves the acetyl groups from the xylose residues of arabinoxylans while cinnamic acid esterases (EC hydrolyze the cinnamic acid derivatives such as ferulic acid and coumaric acids which in turn, may modulate the functionality of cereal arabinoxylans. Finger millet (Eleusine coracana), also known as ragi, is an indigenous minor millet, rich in calcium and dietary fiber. It is extensively consumed in south India, and is used in both native and processed (malted) forms. Till date, the effect of O-acetyl groups and feruloyl groups on the functionality of cereal water-soluble non-starch polysaccharides has not been addressed. Hence, the present study is undertaken as there were no reports on isolation, purification and characterization of finger millet malt esterases i.e. acetic and ferulic acid esterases with respect to their (a) kinetic properties, and (b) role in modulating the functionality of water-soluble non-starch polysaccharides from cereals with respect to their viscosity, foam stabilization and gelling characteristics, which are the most important aspects of polysaccharide functionality. Accordingly, following objectives are envisaged in the present investigation. 1. Standardization of the experimental protocols with respect to the isolation of esterases from finger millet malt, with respect to ionic strength, pH, number of extractions and temperature. Preparation of synthetic substrate(s) for ferulic acid esterases (Feruloyl glycerol). 2. Purification of esterases using fractional precipitation, ion exchange and gel filtration chromatography. Ascertaining apparent homogeneity by native PAGE/SDS-PAGE. Determination of kinetic parameters of esterases i.e. pH, temperature optima and stability. 3. Studying the functional characteristics such as viscosity and foam stabilization of water-soluble polysaccharides of cereals in the presence of enriched enzyme isolates of esterases. 4. Role of esterases with respect to the mechanism of gelling properties of polysaccharides.

Item Type: Thesis (PhD)
Uncontrolled Keywords: Cereal plant cell wall; Arabino xylans; Malting of cereals/millets
Subjects: 600 Technology > 08 Food technology > 16 Nutritive value > 05 Enzymes
600 Technology > 08 Food technology > 21 Cereals > 05 Ragi (Finger Millet)
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: 23 Mar 2010 03:55
Last Modified: 23 Mar 2010 03:55
URI: http://ir.cftri.com/id/eprint/9404

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