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Xylo-oligosaccharides isolated from ragi (Eleusine coracana) bran: determination of their structure and function

Veenashri, B.R. (2015) Xylo-oligosaccharides isolated from ragi (Eleusine coracana) bran: determination of their structure and function. PhD thesis, University of Mysore.

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Abstract

Xylo- oligosaccharides (XOS) are emerging group of prebiotics which are gaining immense attention across the globe. Arabinoxylans which are enriched in cereal and millet brans are one of the ideal sources to obtain xylo-oligosaccharides by endoxylanase treatment. Finger millet, also known as ragi, has very high amount of arabinoxylans and has not been exploited for the isolation, purification and functional characterization of XOS, hence the present study. XOS were obtained from water unextractable polysaccharides by xylanase treatment. Sugar composition of XOS revealed the presence of arabinose and xylose in a relative ratios of 1: 2.4.Cinnamic acid derivatives such as ferulic acid and coumaric acids are found to be major bound phenolic acids in XOS. Finger millet XOS were separated into neutral (~70%, eluted with water, fraction 1) as well as bound phenolic containing XOS {~20 -25%, eluted with methanol/water (1:1), fraction 2}on Amberlite XAD-2 adsorption chromatography. Fraction 2 was further purified on Sephadex LH-20 into three peaks i.e two minor and one major peak. Major peak was structurally characterized by 1H NMR and signals were observed in the range of 3.0-5.0 ppm which are typical of XOS. Signals at 5.3 ppm (H-1) indicated the presence of α- arabinose furanosyl moiety. Signals falling in the range of (a) 6-8 ppm (H-1 to H-5 of ferulic acid), (b) 3.85 (O- methyl group present in the ferulic acid) and (c) 2.10 (Oacetyl groups substituted to xylose) were typical of feruloylated /acetylated XOS. FT- IR absorbance observed at 3600-3200 cm-1 (stretching of the hydroxyl groups both XOS as well as phenolic hydroxyl groups), 1731cm -1 (ester group of ferulic acid), 1596 cm -1 (phenyl ring group) and 1253 cm-1 (conjugated double bonds of ferulic acid) substantiated 1H NMR studies. However the major peak was resolved into two peaks on LC- ESI-MS- TOF indicating the m/z values as 728 (Feruloylated arabino xylotetraose) and with a low signal intensity at m/z 567( O- acetylated feruloyl arabino xylobiose).Antioxidant activity of the feruloyl XOS derived from ragi bran was compared with feruloyl XOS derived from wheat, maize and rice brans by using three different methods i.e. (i) DPPH, (ii)FRAP as well as (iii) β-carotene emulsion assays. Relatively higher anti-oxidant capacity was exhibited by ragi XOS as compared to XOS of cereal brans by DPPH and FRAP assays. α- amylase and α- glucosidase are the key enzymes that have been targeted as potential candidates for modulation of type-2 diabetes associated post prandial hyperglycemia. Tannins, phenolic acids, WSP and XOS were isolated from finger millet bran in 3, 2.4, 0.8 and 7% yields respectively and were taken individually as well as collectively at a concentration of 50 μg and 10 μg for the inhibition of α– amylase and α– glucosidase respectively. The inhibition of these enzymes is of mixed type and was more pronounced when the inhibitors taken together rather than individually. This study clearly indicated the potential of ragi bran derived tannins, phenolic acids, WSP and XOS with respect to the inhibition of both α– amylase and α– glucosidase.

Item Type: Thesis (PhD)
Uncontrolled Keywords: Xylo-oligosaccharides, Arabinoxylans, cereal bran, millet bran, ragi bran
Subjects: 500 Natural Sciences and Mathematics > 07 Life Sciences > 03 Biochemistry & Molecular Biology > 07 Enzyme Biochemistry
600 Technology > 08 Food technology > 21 Cereals > 05 Ragi (Finger Millet)
Divisions: Dept. of Biochemistry
Depositing User: Food Sci. & Technol. Information Services
Date Deposited: 19 May 2016 07:51
Last Modified: 19 May 2016 07:51
URI: http://ir.cftri.com/id/eprint/12180

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